JP2009258268A - Signal processing device and signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively utilize memory resources by reducing the holding number of filter character information of a NC (noise canceling) filter when different NC modes are set so as to be variable, and to reduce user's sense of incongruity due to the change of sound quality when the NC mode is switched. <P>SOLUTION: Filter processing is individually performed by entering a sound collection signal by a microphone, and each filter processing output is combined with a required combination ratio. Thereby, as an intermediate signal characteristic by multiplication of the plurality of filter characteristics is given to the sound collection signal, it is not required that the filter characteristic is related to the NC mode one by one, as in the prior art. Moreover, when the combination ratio is changed with time, sudden change of sound quality is prevented, and user's sense of incongruity is reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a signal processing apparatus and method for performing a filter process for giving a required signal characteristic to a collected sound signal from a microphone, and more particularly to a signal processing apparatus suitable for application to an apparatus having a noise canceling function. And proposes the method.

Japanese Patent Laid-Open No. 3-214892 Japanese Patent Laid-Open No. 3-96199

  A so-called noise canceling system for headphone devices that actively cancels external noise that is heard when playing sound of content such as music with a headphone device is known and put into practical use. ing. As such a noise canceling system, two systems, a feedback system and a feedforward system, are broadly known.

For example, Patent Document 1 discloses an audio signal obtained by inverting the phase of noise (noise) inside an acoustic tube collected by a microphone unit provided in the vicinity of an earphone (headphone) unit in an acoustic tube attached to a user's ear. Is generated and output from the earphone unit as sound, thereby reducing the external noise, that is, the configuration of the noise canceling system corresponding to the feedback method is described.
Further, in Patent Document 2, as a basic configuration, a configuration in which a sound signal obtained by collecting a microphone with a microphone attached to the outer casing of the headphone device is given a characteristic by a predetermined transfer function and output from the headphone device. That is, the configuration of a noise canceling system corresponding to the feedforward method is described.

  Regardless of which of the feedforward method and the feedback method is employed, the filter characteristics set for noise canceling are, for example, that the sound from an external noise source reaches the user's ear position (noise cancellation point). Is set so that noise is canceled at the user's ear position based on various transfer functions such as the spatial transfer function up to and the characteristics of the microphone amplifier / headphone amplifier.

  At present, a filter (NC filter) for noise canceling is configured by an analog circuit. Here, when the NC filter is configured by an analog circuit, for example, when a noise canceling mode (noise canceling characteristic) corresponding to each different noise environment is variably set, different filter characteristics are provided. A plurality of filter circuits having the above are provided, and the noise canceling mode is changed by switching them. However, such a configuration is unrealistic in terms of circuit mounting area and the like, and as a result, the noise canceling mode cannot be selectively set at present.

  In response to such a current situation, the present applicant has previously proposed a configuration in which an NC filter is realized by a digital circuit as a configuration for variably setting a plurality of noise canceling modes. That is, the NC filter is realized by a digital filter using, for example, an FIR (Finite Impulse Response) filter. In the case of such a noise canceling system using a digital filter, the filter characteristics of the NC filter can be changed by changing the configuration of the digital filter and the filter coefficient, which is simpler than the case of using an analog circuit. The noise canceling characteristic (mode) can be changed by the configuration. That is, a configuration in which the noise canceling mode is variably set can be realized as a realistic one.

Here, as understood from the above description, the change of the noise canceling mode is realized by changing the filter characteristic of the NC filter at present. That is, one filter characteristic is associated with one noise canceling mode on a one-to-one basis.
According to such a current method, when the NC filter is configured with a digital filter as described above, the same number of filter characteristic information as the number of noise canceling modes to be variably set (representing the filter configuration and filter coefficients). Parameter information) must be stored in the holding memory.

However, in the future, as a noise canceling system, in addition to variably setting the noise canceling mode for each of several types of noise environments such as outdoors / inside trains / in airplanes, for example, preferences and ear shapes for each user, It is envisaged to variably set the noise canceling mode corresponding to each combination of more items. At this time, if the number of items to be dealt with increases, the number of noise canceling modes to be set according to the combination greatly increases. That is, when the current method as described above is employed, it is necessary to secure a larger memory capacity.
As can be understood from this, the current method in which the noise canceling mode and the filter characteristic are in one-to-one correspondence tends to waste storage resources, and an improvement thereof is desired.

  On the other hand, in a system in which a plurality of noise canceling modes can be arbitrarily switched, switching for shifting from a state in which a certain noise canceling mode is set to a state in which another noise canceling mode is set. In this case, if no consideration is given to the switching process, for example, the switching is instantaneously performed at a certain point in time, a sudden change in the sound quality to the listener There is a risk of giving a sense of incongruity associated with. Specifically, for example, a phenomenon occurs in which the sound quality of a sound that is heard as the background sound of a listening sound such as music changes greatly with the switching, and the sound quality change gives the user a great sense of discomfort. There is a possibility that.

Therefore, in the present invention, the signal processing apparatus is configured as follows in consideration of the above-described problems.
That is, a plurality of filter processing units are provided which respectively give different signal characteristics to the sound pickup signals by inputting the sound pickup signals obtained based on the sound pickup operation by the microphones and individually performing the filter processing.
In addition, a synthesis unit is provided for synthesizing the filter processing outputs from the plurality of filter processing units according to the set synthesis ratio.
Furthermore, a control unit is provided for changing the synthesis ratio of the synthesis unit in a time-varying manner in response to the state in which the signal characteristics to be given to the sound collection signal are to be switched.

In the present invention, the signal processing apparatus is also configured as follows.
That is, a plurality of filter processing means for inputting different sound signal characteristics to the sound pickup signals by inputting the sound pickup signals obtained based on the sound pickup operation by the microphones and individually performing the filtering process are set. Synthesis means for synthesizing the filter processing outputs from the plurality of filter processing means according to the synthesis ratio.

  According to the present invention described above, it is possible to input the collected sound signal obtained based on the sound collecting operation by the microphone and perform the filtering process individually, and synthesize the respective filter processing outputs at the required combining ratio. According to this, it is possible to obtain a state in which an intermediate signal characteristic obtained by multiplying signal characteristics given by a plurality of filter processes is given to the synthesized sound pickup signal. In other words, an intermediate characteristic between the characteristics of each filter process can be given to the collected sound signal. Since the intermediate characteristic of each filter processing characteristic can be given in this way, it is not necessary to have a one-to-one correspondence between the filter characteristic and the signal characteristic to be given to the collected sound signal, for example.

  Further, according to the present invention in which the synthesis ratio is changed in a time-varying manner, when switching the signal characteristics to be given to the collected sound signal, instantaneous switching is performed at a certain time point as in the past. Can be prevented, and a user's uncomfortable feeling accompanying switching of signal characteristics can be reduced.

  As described above, according to the present invention, when a required signal characteristic is given to a sound pickup signal obtained based on a sound pickup operation by a microphone, the sound pickup signal is intermediate between a plurality of filter processing characteristics. Since the characteristics can be given, for example, it is not necessary to have a one-to-one correspondence between the filter characteristics and the signal characteristics to be given to the collected sound signal as in the prior art. According to this, the number of filter characteristic information to be held in the memory can be reduced as compared with the conventional case, and the storage resources can be effectively used.

  In addition, according to the present invention in which the composition ratio is changed in a time-varying manner as described above, when switching the signal characteristics to be given to the sound pickup signal, the instantaneous value from a certain point in time as in the past is changed. It is possible to prevent the switching from being performed, and it is possible to reduce the user's uncomfortable feeling accompanying the switching of the signal characteristics.

Further, if the present invention is applied to a noise canceling system, the number of filter characteristic information to be held in a memory when switching noise canceling characteristics (noise canceling mode) may be significantly reduced as compared with the conventional case. it can. That is, as a configuration that enables switching of the noise canceling mode, it is possible to improve the point that the storage resources are wasted as in the conventional case.
In addition, it is possible to realize an excellent noise canceling system that can reduce the user's uncomfortable feeling accompanying switching of the noise canceling mode.

Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described.
First, prior to describing the configuration of the present embodiment, the basic concept of a noise canceling system will be described.

<Basic concept of noise canceling system>

As a basic system of the noise canceling system, a system in which servo control is performed by a feedback (FeedBack: FB) system and a feedforward (FeedForward: FF) system are known. First, the FB method will be described with reference to FIG.

FIG. 1A schematically shows a model example of a noise canceling system based on the FB method on the right ear (R channel in two-channel stereo with L (left) and R (right)) of a headphone wearer (user). Is shown.
As the structure on the R channel side of the headphone device here, first, in the housing portion 201 corresponding to the right ear, a driver 202 is provided at a position corresponding to the right ear of the user 500 wearing the headphone device. . The driver 202 is synonymous with a so-called speaker having a diaphragm, and is driven (driven) by an amplified output of an audio signal so as to emit sound into space.

In addition, as the FB method, the microphone 203 is provided at a position in the housing portion 201 that is close to the right ear of the user 500. Depending on the microphone 203 provided in this way, the sound output from the driver 202 and the sound that enters the housing part 201 from the external noise source 301 and reaches the right ear, that is, the right ear can be heard. In-housing noise 302, which is an external audio signal, is collected. Note that the noise 302 in the housing is generated because the noise sound source 301 leaks as a sound pressure from a gap such as an ear pad of the housing, or the headphone device casing vibrates due to the sound pressure of the noise sound source 301. It can be mentioned that this is transmitted into the housing part.
Then, in order to cancel (attenuate or reduce) the in-housing noise 302 such as a signal having a reverse characteristic with respect to the audio signal component of the external audio from the audio signal obtained by collecting the sound with the microphone 203. The signal (cancellation audio signal) is generated, and this signal is fed back so as to be synthesized with the sound signal (audio sound source) of the necessary sound for driving the driver 202. As a result, at the noise cancellation point 400 set at a position corresponding to the right ear in the housing portion 201, the external sound is canceled by synthesizing the output sound from the driver 201 and the component of the external sound. A sound is obtained, and this sound is heard by the user's right ear. By providing such a configuration also on the L channel (left ear) side, a noise canceling system as a headphone device corresponding to normal L, R2 channel stereo can be obtained.

  The block diagram in FIG. 1B shows a basic model configuration example of the noise canceling system based on the FB method. FIG. 1B shows a configuration corresponding only to the R channel (right ear) side as in FIG. 1A, and the L channel (left). A similar system configuration can be provided for the (ear) side. Further, the block shown in this figure indicates one specific transfer function corresponding to a specific circuit part, circuit system, etc. in the system of the noise canceling system by the FB method, and is referred to as a transfer function block here. To. The character shown in each transfer function block represents the transfer function of the transfer function block, and each time a voice signal (or voice) passes through the transfer function block, the transfer function shown there Will be given.

  First, the sound collected by the microphone 203 provided in the housing unit 201 is a transfer function block corresponding to the microphone 203 and a microphone amplifier that amplifies the electric signal obtained by the microphone 203 and outputs a sound signal. It is obtained as an audio signal via 101 (transfer function M). The audio signal that has passed through the transfer function block 101 is input to the synthesizer 103 via the transfer function block 102 (transfer function −β) corresponding to the FB (FeedBack) filter circuit. The FB filter circuit is a filter circuit in which characteristics for generating the above-described cancellation audio signal are set from the audio signal obtained by collecting the sound with the microphone 203, and the transfer function thereof is expressed as -β. It is what.

In addition, the audio signal S of the audio sound source that is the content such as music is assumed to be equalized by an equalizer here, and a synthesizer is connected via a transfer function block 107 (transfer function E) corresponding to the equalizer. 13 is input.
In the FB method, the sound signal S is equalized in this way. In the FB method, a noise-collecting microphone 203 is provided in the housing portion 201, and not only the noise sound but also the output sound from the driver 202 is collected. It comes from that. That is, since the microphone 203 also collects the component of the audio signal S in this way, the transfer function −β is given to the audio signal S in the FB method. There is a risk of sound quality degradation. Therefore, in order to suppress deterioration in sound quality due to the transfer function -β, the required signal characteristics are given to the audio signal S by equalizing.

  The synthesizer 103 synthesizes the above two signals by addition. The synthesized audio signal is amplified by the power amplifier and output to the driver 202 as a drive signal, so that the driver 202 outputs the audio signal. That is, the sound signal from the synthesizer 103 passes through the transfer function block 104 (transfer function A) corresponding to the power amplifier, and further passes through the transfer function block 105 (transfer function D) corresponding to the driver 202 as sound. Released into the space. Note that the transfer function D of the driver 202 is determined by the structure of the driver 202, for example.

  Then, the sound output from the driver 202 passes through the transfer function block 106 (transfer function H) corresponding to the spatial path (spatial transfer function) from the driver 202 to the noise cancel point 400. And is synthesized with the noise 302 in the housing in that space. As the sound pressure P of the output sound that reaches the right ear, for example, from the noise cancellation point 400, the sound of the noise sound source 301 that enters from the outside of the housing portion 201 is canceled.

この[式１]において、ハウジング内ノイズ３０２であるＮに着目すると、Ｎは、１ ／（１＋ＡＤＨＭβ）で表される係数により減衰されることがわかる。 Here, in the model of the noise canceling system shown in FIG. 1B, the sound pressure P of the output sound is N in the noise 302 in the housing and S in the sound signal of the audio sound source. Thus, using the transfer function “M, −β, E, A, D, H” shown in each transfer function block, it is expressed as the following [Equation 1].

In this [Equation 1], when attention is paid to N which is the noise 302 in the housing, it is understood that N is attenuated by a coefficient represented by 1 / (1 + ADHMβ).

However, in order for the system of [Equation 1] to operate stably without oscillating in the noise reduction target frequency band, the following [Equation 2] must be satisfied.

As a general matter, the absolute value of the product of each transfer function in the noise canceling system by the FB method is

1 << | ADHMβ |

In combination with Nyquist's stability discrimination in classical control theory, [Equation 2] can be interpreted as follows.
Here, in the system of the noise canceling system shown in FIG. 1B, a system represented by (−ADHMβ) obtained by cutting a loop portion related to N, which is the noise 302 in the housing, is considered. . This system is called “open loop” here. As an example, if the transfer function block 101 corresponding to the microphone and the microphone amplifier and the transfer function block 102 corresponding to the FB filter circuit are to be disconnected, the above open loop can be formed.

The above open loop has the characteristics shown by the Bode diagram of FIG. 2, for example. In this Bode diagram, the horizontal axis represents frequency, and the vertical axis represents gain in the lower half and phase in the upper half.
When this open loop is targeted, the following two conditions must be satisfied in order to satisfy [Equation 2] based on Nyquist stability determination.
Condition 1: Phase 0 deg. When passing through the (0 degree) point, the gain must be less than 0 dB.
Condition 2: When the gain is 0 dB or more, the phase is 0 deg. Do not include the point.

When the above two conditions 1 and 2 are not satisfied, positive feedback is applied to the loop, causing oscillation (howling). In FIG. 2, phase margins Pa and Pb corresponding to the above condition 1 and gain margins Ga and Gb corresponding to the condition 2 are shown. If these margins are small, the possibility of oscillation increases due to various individual differences of the user who uses the headphone device to which the noise canceling system is applied, and variations in the state when the headphone device is worn.
For example, in FIG. 2, the phase 0 deg. The gain when passing through the point is smaller than 0 dB, and gain margins Ga and Gb are obtained accordingly. However, for example, if phase 0 deg. The gain when passing through the point is 0 dB or more and the gain margins Ga and Gb are eliminated, or the phase is 0 deg. Although the gain when passing through this point is less than 0 dB, when the gain margins Ga and Gb are close to 0 dB and the gain margins Ga and Gb become small, oscillation occurs or the possibility of oscillation increases.
Similarly, in FIG. 2, when the gain is 0 dB or more, the phase is 0 deg. The phase margins Pa and Pb are obtained. However, for example, when the gain is 0 dB or more, the phase 0 deg. The point has been passed. Alternatively, the phase 0 deg. When the phase margins Pa and Pb become small and the phase margins become small, oscillation occurs or the possibility of oscillation increases.

Next, in the configuration of the FB type noise canceling system shown in FIG. 1B, in addition to the above-described external sound (noise) canceling (reducing) function, necessary sound (necessary sound) is output by the headphone device. A case of reproduction output will be described.
Here, as a necessary sound, for example, an audio signal S of an audio source as content such as music is shown.
Note that the audio signal S may be other than the musical or similar content. For example, when the noise canceling system is applied to a hearing aid or the like, a microphone provided outside the housing for collecting the necessary sound around the microphone (different from the microphone 203 provided in the noise cancellation system) The sound signal obtained by collecting the sound. In addition, when applied to what is called a so-called headset, it becomes an audio signal such as a speech of the other party received by communication such as telephone communication. That is, the audio signal S corresponds to general audio that needs to be reproduced and output according to the use of the headphone device.

なお、この伝達特性Ｅは、周波数軸でみた場合に、上記オープンループに対してほぼ逆特性（１＋オープンループ特性）となっている。そして、この[式３]により示される伝達関数Ｅの式を、[式１]に代入すると、図１（ｂ）に示されるノイズキャンセリングシステムのモデルにおける出力音の音圧Ｐについては、次の[式４]のようにして表すことができる。

[式４]におけるＡＤＨＳの項において示される伝達関数Ａ、Ｄ、Ｈのうち、伝達関数Ａはパワーアンプに対応し、伝達関数Ｄはドライバ２０２に対応し、伝達関数Ｈはドライバ２０２からノイズキャンセル点４００までの経路の空間伝達関数に対応するので、ハウジング部２０１内のマイクロフォン２０３の位置が耳に対して近接した位置にあるとすれば、音声信号Ｓについては、ノイズキャンセル機能を有さないようにした通常のヘッドフォンと同等の特性が得られることがわかる。 First, in the above [Expression 1], attention is paid to the audio signal S of the audio sound source. Then, it is assumed that the transfer function E corresponding to the equalizer is set to have a characteristic represented by the following [Equation 3].

The transfer characteristic E is almost opposite to the open loop (1 + open loop characteristic) when viewed on the frequency axis. Then, when the expression of the transfer function E expressed by [Expression 3] is substituted into [Expression 1], the sound pressure P of the output sound in the model of the noise canceling system shown in FIG. [Equation 4].

Of the transfer functions A, D, and H shown in the ADHS term in [Equation 4], the transfer function A corresponds to the power amplifier, the transfer function D corresponds to the driver 202, and the transfer function H is noise cancelled from the driver 202. Since it corresponds to the spatial transfer function of the path to the point 400, if the position of the microphone 203 in the housing portion 201 is close to the ear, the audio signal S does not have a noise canceling function. It turns out that the characteristic equivalent to the normal headphones made like this is obtained.

Next, a noise canceling system using the FF method will be described.
FIG. 3A shows a configuration on the side corresponding to the R channel as in FIG. 1A as a model example of the noise canceling system using the FF method.
In the FF method, the microphone 203 is provided outside the housing unit 201 so that sound that is supposed to arrive from the noise sound source 301 can be collected. Then, the external sound collected by the microphone 203, that is, the sound that is assumed to have arrived from the noise sound source 301 is collected to obtain a sound signal, and an appropriate filtering process is performed on the sound signal to cancel the audio signal. To be generated. Then, the canceling audio signal is synthesized with the necessary sound signal. That is, the canceling audio signal that electrically simulates the acoustic characteristics from the position of the microphone 203 to the position of the driver 202 is synthesized with the sound signal of the necessary sound.
The sound signal obtained by synthesizing the canceling audio signal and the necessary sound signal is output from the driver 202 in this way, and the sound obtained at the noise canceling point 400 is output from the noise sound source 301 to the housing portion 201. You can hear the sound that has entered inside is canceled.

FIG. 3B shows a configuration on the side corresponding to one channel (R channel) as a basic model configuration example of the noise canceling system by the FF method.
First, the sound collected by the microphone 203 provided outside the housing part 201 is obtained as an audio signal through the transfer function block 101 having the transfer function M corresponding to the microphone 203 and the microphone amplifier.
Next, the audio signal that has passed through the transfer function block 101 is input to the synthesizer 103 via the transfer function block 102 (transfer function −α) corresponding to an FF (FeedForward) filter circuit. The FF filter circuit 102 is a filter circuit in which a characteristic for generating the above-described cancellation audio signal is set from the audio signal obtained by collecting the sound with the microphone 203, and its transfer function is represented as -α. It is what.

The audio signal S of the audio source here is directly input to the synthesizer 103.
The audio signal synthesized by the synthesizer 103 is amplified by a power amplifier and output to the driver 202 as a drive signal, so that the audio signal is output from the driver 202. That is, also in this case, the audio signal from the synthesizer 103 passes through the transfer function block 104 (transfer function A) corresponding to the power amplifier, and further passes through the transfer function block 105 (transfer function D) corresponding to the driver 202. It is emitted into the space as sound.
The sound output by the driver 202 reaches the noise cancellation point 400 via the transfer function block 106 (transfer function H) corresponding to the spatial path (spatial transfer function) from the driver 202 to the noise cancellation point 400. In this case, the noise is combined with the noise 302 in the housing.

In addition, a path from the noise source 301 to the noise cancellation point 400 until the sound emitted from the noise source 301 enters the housing portion 201 and reaches the noise cancellation point 400, as shown as the transfer function block 110. Is given a transfer function (spatial transfer function F). On the other hand, the microphone 203 collects sound that is supposed to arrive from the noise sound source 301 that is external sound, and at this time, the sound (noise) emitted from the noise sound source 301 is picked up. Until reaching, a transfer function (spatial transfer function G) corresponding to the path from the noise source 301 to the microphone 203 is given as shown as the transfer function block 111. As the FF filter circuit corresponding to the transfer function block 102, the transfer function −α is set in consideration of the above-described spatial transfer functions F and G.
Thereby, as the sound pressure P of the output sound that reaches the right ear from the noise cancellation point 400, for example, the sound of the noise sound source 301 entering from the outside of the housing portion 201 is canceled.

また、理想的には、ノイズ音源３０１からキャンセルポイント４００までの経路の伝達関数Ｆは、次の[式６]のようにして表すことができる。

次に、[式６]を[式５]に代入すると、右辺の第１項と第２項とが相殺されることとなる。この結果から、出力音の音圧Ｐは、以下の[式７]のようにして表すことができる。

In the model of the noise canceling system based on the FF method shown in FIG. 3B, the sound pressure P of the output sound is N as noise generated in the noise sound source 301 and S as the sound signal of the audio sound source. In addition, the transfer function “M” shown in each transfer function block
, −α, E, A, D, H ”, is expressed by the following [Formula 5].

Ideally, the transfer function F of the path from the noise source 301 to the cancellation point 400 can be expressed as the following [Equation 6].

Next, substituting [Expression 6] into [Expression 5] cancels out the first and second terms on the right side. From this result, the sound pressure P of the output sound can be expressed as [Equation 7] below.

In this way, it is indicated that the sound that is supposed to arrive from the noise sound source 301 is canceled and only the sound signal of the audio sound source is obtained as sound. That is, theoretically, the user's right ear can hear a noise-cancelled voice. However, in reality, it is very difficult to construct a complete FF filter circuit that can provide a transfer function that fully satisfies [Equation 6]. In addition, there are relatively large individual differences in the shape of the ears of a person and the manner in which the headphone device is worn, and the change in the relationship between the position where noise occurs and the position of the microphone is particularly affected by noise in the mid-high frequency band. It is known to affect the reduction effect. For this reason, with regard to the mid-high range, active noise reduction processing is refrained, and passive sound insulation mainly depending on the structure of the housing of the headphone device is often performed.
For confirmation, [Expression 6] means that the transfer function of the path from the noise source 301 to the ear is imitated by an electric circuit including the transfer function -α.

Further, in the FF type noise canceling system shown in FIG. 3A, since the microphone 203 is provided outside the housing, the cancellation point 400 is the same as that of the FB type noise canceling system shown in FIG. Differently, it can be arbitrarily set in the housing part 201 so as to correspond to the ear position of the listener. However, the transfer function −α is usually fixed, and is determined for some target characteristic at the design stage. On the other hand, the ear shape and the like vary depending on the listener. For this reason, there may be a phenomenon that a sufficient noise canceling effect cannot be obtained or a noise component is added in a non-reverse phase to generate an abnormal sound.
For this reason, the FF method is generally considered to have a low possibility of oscillation and high stability, but it is difficult to obtain a sufficient noise attenuation amount (cancellation amount). On the other hand, in the FB method, a large amount of noise attenuation can be expected, but attention should be paid to the stability of the system. Thus, the FB method and the FF method have their characteristics.

<First Embodiment>
[Configuration of headphone device]

FIG. 4 is a block diagram showing an internal configuration of the headphone device 1 as an embodiment of the signal processing device of the present invention.
First, the headphone 1 is provided with a microphone MIC as a configuration corresponding to the noise canceling system. As shown in the figure, the collected sound signal from the microphone MIC is amplified by the microphone amplifier 2, converted to a digital signal by the A / D converter 3, and supplied to a DSP (Digital Signal Processor) 5. The Hereinafter, the sound collection signal converted into a digital signal by the A / D converter 3 is also referred to as sound collection data.

  Here, the headphone 1 shown in FIG. 4 corresponds to a feed forward (FF) system as a noise canceling system. As can be seen with reference to FIG. 3A, in the headphone device corresponding to the FF system, the microphone MIC (the microphone 203 in FIG. 3) is provided so as to be disposed outside the housing portion (201). . Specifically, the microphone MIC in this case is provided so as to collect sound (noise sound) generated in the outside of the housing portion of the headphones 1.

In FIG. 4, an audio signal (sound signal) supplied from an external player such as an audio player is input to the headphone 1 via an audio input terminal TAin in the figure and input from the audio input terminal TAin. The audio signal is supplied to the DSP 5 via the A / D converter 4.
For confirmation, the audio signal input from the audio input terminal TAin is a listening audio signal that is input to be listened to by the user wearing the headphones 1. In other words, it is an audio signal that should not be subject to noise canceling.

The DSP 5 executes digital signal processing based on the signal processing program 8a stored in the memory 8 in the figure, thereby realizing the operation as each functional block shown in the figure.
Here, hereinafter, for convenience, each functional block of the DSP 5 may be described as being handled as hardware. In the following, noise canceling is abbreviated as “NC”.

  First, sound collection data input to the DSP 5 via the A / D converter 3 described above is supplied to each of the first NC filter 5a1 and the second NC filter 5a2. Each of these NC filters 5a is composed of, for example, an FIR (Finite Impulse Response) filter, and performs a filtering process to give a required signal characteristic to the collected sound data.

  The first NC filter 5a1 and the second NC filter 5a2 have their filter configurations and filter coefficients variably set by a filter characteristic / mix ratio control unit 5e described later. That is, the filter characteristics (filter processing characteristics) of the first NC filter 5a1 and the second NC filter 5a2 can be variably set.

Here, the memory 8 connected to the DSP 5 stores a plurality of pieces of filter characteristic information for obtaining different noise canceling characteristics as the filter characteristic information 8b in the figure. The individual filter characteristic information is information necessary for setting the filter characteristic of the NC filter 5a, and specifically represents the above-described filter configuration / filter coefficient that determines the filter characteristic of the NC filter 5a. Parameter information.
As will be described later, the filter characteristic / mix ratio control unit 5e sets the filter characteristics of the first NC filter 5a1 and the second NC filter 5a2 based on the filter characteristic information 8b stored in the memory 8. Thereby, filter characteristics for noise canceling are set in the first NC filter 5a1 and the second NC filter 5a2, and the signal characteristics for noise canceling are respectively added to the collected sound data. To be given.

  The collected sound data provided with the signal characteristic for noise canceling by the first NC filter 5a1 is collected to the first multiplier 5b1, and the collected sound data provided with the signal characteristic for noise canceling by the second NC filter 5a2. The data is supplied to the second multiplier 5b2. Each of these multipliers 5b gives the coefficient (gain) given from the filter characteristic / mix ratio controller 5e to the input data.

  The respective sound collection data given the coefficients by the multipliers 5b are supplied to the adder 5c. The adder 5c adds (synthesizes) the collected sound data to which the coefficients are given by the multipliers 5b.

  Here, depending on the first multiplier 5b1, the second multiplier 5b2, and the adder 5c, the filter processing outputs from the first NC filter 5a1 and the second NC filter 5a2 are weighted by the set coefficients and combined ( Mix). That is, the first multiplication unit 5b1, the second multiplication unit 5b2, and the addition unit 5c function as a combining unit that combines the respective filter processing outputs with a set combination ratio.

The addition (synthesis) output from the adder 5c is supplied to the adder 5d.
As shown in the figure, the adder 5d receives a listening audio signal (audio data) input from the above-described audio input terminal TAin via the A / D converter 4, and the adder 5d The audio data for use and the synthesized output from the adder 5c are added.
Data obtained by the adding unit 5d is referred to as addition data. This added data includes a component of collected sound data to which signal characteristics for noise canceling are given by the NC filter 5a. Therefore, the sound reproduction based on the added data is performed by the driver DRV described later, so that the user wearing the headphones 1 can perceive that the noise component has been canceled (reduced). That is, a sound other than the sound based on the audio data for listening is canceled and listened to.

  In addition, the DSP 5 is configured to realize an operation according to the present embodiment, which will be described later, by a functional operation as the filter characteristic / mix ratio control unit 5e, and the functional operation as the filter characteristic / mix ratio control unit 5e. Will be described later.

The added data obtained by the DSP 5 as described above is supplied to the D / A converter 6 and converted into an analog signal, then amplified by the power amplifier 7 and supplied to the driver DRV.
The driver DRV includes a diaphragm, and the diaphragm is configured to be driven based on an audio signal (drive signal) supplied from the power amplifier 7, so that an audio output (sound reproduction) based on the audio signal is performed. ).

The microcomputer 10 includes, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processing Unit), and the like, and performs various control processes and operations based on programs stored in the ROM, for example. By doing so, overall control of the headphones 1 is performed.
As shown in the figure, an operation unit 9 is connected to the microcomputer 10. For example, the operation unit 9 includes an operation element (not shown) provided so as to be exposed on the outer surface of the casing of the headphones 1, and the user performs various operation inputs. Information input through the operation unit 9 is transmitted to the microcomputer 10 as operation input information. The microcomputer 10 performs necessary calculations and control in accordance with the input information.
For example, as an operation element provided in the operation unit 9, a power button for instructing to turn on / off the power of the headphones 1 can be cited. The microcomputer 10 performs power on / off control of the headphones 1 based on the operation input information supplied from the operation unit 9 in response to the operation of the power button.
Further, examples of the operation element provided in the operation unit 9 include a selection button for performing an NC mode selection operation. The microcomputer 10 selects the NC mode to be newly set based on the operation input information supplied from the operation unit 9 according to the operation of the selection button, and selects the selected NC mode DSP 5 (filter characteristics / mix ratio). An instruction is given to the control unit 5e).

Here, the NC mode in which the headphones 1 can be set will be described with reference to FIG.
FIG. 5 illustrates frequency-noise reduction characteristics (also simply referred to as noise reduction characteristics) for each NC mode, with the horizontal axis representing frequency (Hz) and the vertical axis representing noise reduction (dB). That is, the NC characteristic for each NC mode is illustrated. In FIG. 5, for example, NC mode 1, NC mode 2, and NC mode 3 are illustrated as NC modes. The solid line is NC mode 1, the broken line is NC mode 2, and the alternate long and short dash line is NC mode 3. Respectively.
As shown in this figure, each NC mode has different noise reduction characteristics.

[Crossfade switching]

Here, as can be understood from the above description, in the headphone 1 of the present embodiment, the NC mode is variably set, that is, the NC characteristic is variably set. As described above, when the NC mode is variably set, when switching from a state in which a certain NC characteristic is obtained to a state in which another NC characteristic is obtained, a certain point in time is used as a boundary. If no consideration is given to switching processing, such as switching instantaneously, there is a risk that the listener may feel uncomfortable with a sudden change in sound quality.

  Therefore, in the present embodiment, when such NC mode (NC characteristics) is switched, each NC filter 5a applies a filter process with a different characteristic to the collected sound signal, and then the filters of those NC filters 5a. A method of cross-fading each filter processing output so that the composition ratio of the processing outputs is changed with the passage of time so that the NC characteristics that have been set so far are gradually changed to the NC characteristics that should be newly set. Take.

  Hereinafter, such a crossfade switching operation as the present embodiment will be described with reference to FIGS. The operations described below are functional operations as the filter characteristic / mix ratio control unit 5e shown in FIG.

FIG. 6 is a diagram illustrating an example in which the number of NC modes is simply three as a diagram for explaining the cross-fade switching operation of the present embodiment. In FIG. 6, for the sake of simplicity, an example in which the NC mode (NC characteristic) and the filter characteristic correspond one-to-one will be described. That is, in setting a certain NC mode (NC characteristic), the filter characteristic corresponding to one NC filter 5a is set and the ratio of the filter processing output is set to one.
Specifically, here, it is assumed that three modes of NC mode 1, NC mode 2, and NC mode 3 can be set as the NC mode, and the correspondence relationship between the NC mode and the filter characteristic is NC mode 1: filter characteristic A, NC mode 2: filter characteristic B, NC mode 3: filter characteristic C.

First, in FIG. 6A, it is assumed here that the state before switching is a state in which the NC characteristic by the filter characteristic A is obtained. That is, it is assumed that NC mode 1 has been set.
Then, it is assumed that the NC mode 3 is newly selected by the user operation and the NC characteristic based on the filter characteristic C is to be set as shown in the figure.

In response to this, first, a filter characteristic corresponding to the newly selected NC mode is set for the non-operating NC filter 5a out of the first NC filter 5a1 and the second NC filter 5a2. Here, in the state before the switching, as the setting state of the NC mode 1, the filter characteristic A is set to any one of the NC filters 5a, and the ratio of the filter processing output is set to “1” and supplied to the adding unit 5d. Will be. At this time, the other NC filter 5a does not need to be operated, and is in a non-operating state.
When a new NC mode is selected as described above and the state to be switched to the selected NC mode is entered, first, a new selection is made for the NC filter 5a on the non-operating side. The filter characteristics for realizing the selected NC mode are set, and the switching standby state is set. Specifically, in this case, the filter characteristic C corresponding to the newly selected NC mode 3 is set.

After that, crossfading is performed as indicated by the broken-line arrows in FIG. Specifically, in this case, each NC filter 5a is set so that a composition ratio of A: C = 0: 1 is obtained from a state where the composition ratio is A: C = 1: 0 in the switching standby state. The output ratio is gradually changed with time (time-varying).
For example, in the switching standby state, the filter characteristic A is set in the first NC filter 5a1 and the filter characteristic C is set in the second NC filter 5a2, and "the coefficient of the first multiplier 5b1: the coefficient of the second multiplier 5b2" is If the setting state is 1: 0, the coefficient of the first multiplier 5b1 is gradually decreased from 1 to 0, and conversely, the coefficient of the second multiplier 5b2 is increased so as to be 0 → 1. Crossfade switching will be performed.
In this way, as the crossfade switching operation in this case, the coefficient of the multiplier 5b that inputs the output of the NC filter 5a in which the filter characteristic corresponding to the NC mode before switching is set is gradually changed from 1 to 0. This is performed by gradually increasing the coefficient of the multiplier 5b that receives the output of the NC filter 5a that has been lowered and set the filter characteristics corresponding to the NC mode to be newly set from 0 to 1.

FIG. 7 is a diagram illustrating a specific crossfade characteristic.
In FIG. 7, in both FIGS. 7 (a) and 7 (b), the horizontal axis represents time (t), and the vertical axis represents the coefficient (ratio) given by the multiplier 5b. A solid line in the figure indicates a change in a coefficient (hereinafter referred to as a fade-out side coefficient) of a multiplier 5b that inputs an output of the NC filter 5a in which a filter characteristic corresponding to the NC mode before switching is set, and a broken line indicates The figure shows a change in the coefficient (referred to as a fade-in side coefficient) of the multiplier 5b that inputs the output of the NC filter 5a in which the filter characteristic corresponding to the NC mode to be newly set is set.

  First, FIG. 7A shows an example in which the ratio is changed constantly with respect to time. That is, the slope of the fade-out side coefficient and the slope of the fade-in side coefficient are the same.

FIG. 7B shows a characteristic example when the ratio is changed non-constantly with respect to time, and the amount of change with time of the fade-out side coefficient and the fade-in side coefficient is made different. Yes.
Specifically, in the cross-fade characteristic of FIG. 7B, the amount of change of the fade-out side coefficient gradually increases with time, and conversely, the amount of change of the fade-in side coefficient gradually increases with time. I try to make it smaller.

  Note that the cross-fade characteristic should not be limited to that shown in FIG. 7, but may be other characteristics such as, for example, a ratio that changes each ratio according to a trigonometric function.

  Here, in FIG. 6, the case where the NC mode and the filter characteristic correspond to each other in a one-to-one correspondence is illustrated, but in this embodiment, one NC mode is realized with one filter characteristic as described above. In addition, an NC mode can be realized by multiplying a plurality of filter characteristics.

As described above, as a noise canceling system, for example, in addition to variably setting the NC mode (NC characteristic) for each of several types of noise environments such as outdoors / inside a train / in an airplane, for example, for each user It has been envisaged to variably set NC characteristics according to combinations of more items such as preferences and ear shapes.
At this time, if the number of items to be dealt with increases, the number of NC characteristics to be set according to the combination greatly increases. When the method of associating the NC mode (NC characteristic) and the filter characteristic on a one-to-one basis as described above, the type of the NC characteristic to be set increases, and accordingly, the filter characteristic information is stored in the memory 8 accordingly. The amount of information stored as 8b must also be increased. Therefore, the storage resource tends to be wasted only by adopting a method of making one filter characteristic correspond to one NC mode.

For this reason, in the present embodiment, as shown in FIG. 4, the filter processing outputs from the NC filters 5a can be synthesized at a required ratio, and a plurality of filter characteristics can be obtained by multiplying the filter processing outputs. NC characteristics can be realized by combining the above.
If a plurality of filter characteristics can be combined in this way, there is no need to adopt a conventional method of holding one filter characteristic information in association with one NC characteristic, and the memory capacity required for holding the filter characteristic information can be reduced. Can be reduced. That is, this makes it possible to effectively use the storage resource as the memory 8.

  FIGS. 8 and 9 are diagrams for explaining the cross-fade switching operation performed in response to switching between intermediate NC characteristics (NC mode) by combining a plurality of filter characteristics as described above. The relationship between the NC characteristic before switching and the NC characteristic after switching is shown, and FIG. 9 shows an actual operation example. 9A, 9B, and 9C, the first NC filter 5a1, the second NC filter 5a2, the first multiplier 5b1, the second multiplier 5b2, and the adder among the functional blocks of the DSP 5 are shown. 5c is extracted and shown.

First, in FIG. 8, it is assumed here that the NC characteristic before switching (that is, the NC characteristic of the NC mode that has been selected so far) is a characteristic obtained by combining the filter characteristic A and the filter characteristic B. Specifically, it is assumed that the composite ratio of A: B = 0.7: 0.3 is set (this state is referred to as state 1).
The NC characteristic after switching (the NC characteristic of the newly selected NC mode) is a characteristic obtained by combining the filter characteristic A and the filter characteristic C. Specifically, the composition is A: C = 0.3: 0.7. It is assumed that the ratio is set (state 3).

Here, in the case of the present embodiment, when transitioning from the state 1 before switching to the state 3 after switching, as shown in the state 2 in the figure, the ratio of one filter characteristic is 1, and the other filter The characteristic ratio is zero. This is because the number of NC filters 5a is two.
That is, in the state 1, the filter characteristic A is set for one NC filter 5a and the filter characteristic B is set for the other NC filter 5a. It is necessary to reset the filter characteristic of the other NC filter 5a to "C" while maintaining the state where the characteristic A is set. For this reason, as the state 2 in the figure, a state in which the ratio of one filter characteristic (in this case, the filter characteristic B) is always set to 0 is passed. The filter characteristic (in this case, filter characteristic C) necessary for this can be newly set.

9A, 9B, and 9C show the setting state of the filter characteristic of each NC filter 5a corresponding to the transition from state 1 to state 2 to state 3 in FIG. 8, and the first multiplication unit 5b1 and the second multiplication. The coefficient setting state of the part 5b2 is shown.
First, in state 1, it is assumed that the filter characteristic A is set in the first NC filter 5a1 and the filter characteristic B is set in the second NC filter 5a2 as shown in FIG. 9A. In this case, the coefficient of the first multiplier 5b1 that inputs the output of the first NC filter 5a1 in which the filter characteristic A is set is "0.7", and the output of the second NC filter 5a2 in which the filter characteristic B is set is input. The coefficient of the 2 multiplier 5b2 is set to "0.3".
From this state 1, the coefficient of the first multiplier 5b1 is gradually changed from "0.7" to "1", and the coefficient of the second multiplier 5b2 is gradually changed from "0.3" to "0". : The synthesis ratio of the filter characteristic B is set to 1: 0.

As described above, when the ratio of the filter processing output of the second NC filter 5a2 is “0”, the filter characteristic C necessary for obtaining the target NC characteristic in the second NC filter 5a2 is obtained as the state 2 in FIG. 9B. Set a new one.
By gradually changing the coefficient of the first multiplier 5b1 from "1" to "0.3" and the coefficient of the second multiplier 5b2 from "0" to "0.7" from the state 2 as shown in FIG. The state as the state 3 shown in 9 (c) is obtained. That is, the crossfade switching operation from the NC characteristic based on “filter characteristic A: filter characteristic B = 0.7: 0.3” to the NC characteristic based on “filter characteristic A: filter characteristic C = 0.3: 0.7” is completed.

Here, in the headphone 1 of the present embodiment, the switching between the intermediate NC characteristics by the combination of the plurality of filter characteristics is realized with the single filter characteristics as described in FIG. It is possible to perform both switching between NC characteristics.
As described above, the switching operation in the case of FIG. 6 includes setting the filter characteristics corresponding to the newly selected NC mode for the non-operating NC filter 5a, and then operating the other operation. The ratio of the filter processing output of the NC filter 5a on the side is gradually decreased from 1 to 0, and the ratio of the filter processing output of the non-operating NC filter 5a is gradually increased from 0 to 1, so that the synthesis ratio Will change over time.
On the other hand, the switching operations in FIGS. 8 and 9 described above are common in that the cross-fading is performed by changing the synthesis ratio of the respective filter processing outputs in a time-varying manner. For example, an operation different from the case of FIG. 6 is performed.

  As can be understood from this, switching between NC characteristics realized by a single filter characteristic as described in FIG. 6 and switching between intermediate NC characteristics described in FIGS. In the case of dealing with both of these, it is necessary to perform different operations according to the division of the cases. Hereinafter, a series of operations of the crossfade switching operation according to the present embodiment including such case classification will be described.

  First, in the case of the present embodiment, a new NC mode is selected by the microcomputer 10 based on a user operation input via the operation unit 9 of FIG. When a new NC mode is selected based on an operation input, information representing the selected NC mode is supplied from the microcomputer 10 to the DSP 5 (filter characteristic / mix ratio control unit 5e).

In response to this, the filter characteristic / mix ratio control unit 5e first determines the NC characteristic of the NC mode that has been selected (current NC characteristic) and the NC characteristic of the newly selected NC mode (new NC characteristic). The route from the current NC characteristic to the new NC characteristic is obtained by calculation. In the case of FIG. 6, this route is a route from the NC characteristic obtained from the filter characteristic A (NC characteristic of the NC mode 1) directly to the NC characteristic (NC characteristic of the NC mode 3) by the filter characteristic C ( That is, it is obvious that a route that does not pass through the filter characteristic B) is preferable.
In this way, when the current NC characteristic and the new NC characteristic can be realized with one corresponding filter characteristic, a route from the current NC characteristic directly to the new NC characteristic is obtained.

In the case of FIG. 8, after passing through the NC characteristic by “Filter characteristic A: Filter characteristic B = 1: 0” from the NC characteristic by “Filter characteristic A: Filter characteristic B = 0.7: 0.3”, A path to the NC characteristic according to “characteristic A: filter characteristic C = 0.3: 0.7” is obtained.
In other words, both the current NC characteristic and the new NC characteristic are a combination of a plurality of filter characteristics, and the combination of the filter characteristics necessary for realizing the current NC characteristic and the new NC characteristic are necessary. When the combination of the filter characteristics is different, the path is conditioned on the condition that the ratio of the filter characteristics (filter characteristic B in the case of FIG. 8) necessary only on the current NC characteristic side is 0. The route will be determined. As a result, it is possible to obtain a route after satisfying the constraint when the number of NC filters 5a is two.
In view of the configuration of the present system, it is obvious that it is preferable to obtain a path that can eliminate unnecessary filter characteristic replacement (the least number of filter characteristic replacements) as the path in this case. It is.

  When the path is calculated as described above, it is determined from the calculation result whether it is necessary to set the ratio of one of the NC filters 5a to 0 in the middle of the path. That is, by this determination, it is determined whether or not the change setting of the filter characteristic for one NC filter 5a is necessary during the NC characteristic cross-fade switching.

  As a result of this determination, if it is not necessary to set the ratio of any NC filter 5a to 0 in the middle of the route, a new NC characteristic (target) is added to the non-operating NC filter 5a as described in FIG. After setting the filter characteristics for obtaining (NC characteristics), crossfading is performed until “filter processing output of the non-operating NC filter 5a: filter processing output of the operating NC filter 5a = 1: 0”. . That is, the ratio of the filter processing output of the non-operating NC filter 5a is gradually increased from 0 to 1, and the ratio of the filter processing output of the operating NC filter 5a is gradually decreased from 1 to 0.

As a result of the determination, if it is necessary to set the ratio of one of the NC filters 5a to 0 in the middle of the path, first, the NC filter having the filter characteristic set only on the current NC characteristic side is set. Crossfading is performed so that the ratio of the filter processing output of 5a is 0 and the ratio of the filter processing output of the other NC filter 5a is 1. That is, in the examples of FIGS. 8 and 9, the coefficient of the second multiplier 5b2 that inputs the output of the second NC filter 5a2 in which the filter characteristic B necessary only on the current NC characteristic side is set gradually decreases toward zero. It corresponds to gradually increasing the coefficient of the first multiplier 5b1 to which the output of the first NC filter 5a1 is input toward 1.
Then, after setting a filter characteristic for obtaining the target NC characteristic for the NC filter 5a whose ratio is 0, the ratio of the filter processing output of the NC filter 5a that has been set, and the other Crossfading is performed until the ratio of the filter processing output of the NC filter 5a reaches the target ratio. That is, in the examples of FIGS. 8 and 9, after setting the filter characteristic C for obtaining the target NC characteristic in the second NC filter 5a2, the coefficient of the second multiplier 5b2 for inputting the output of the second NC filter 5a2 is set. This is equivalent to gradually increasing toward the target ratio of 0.7 and gradually decreasing the coefficient of the second multiplier 5b2 that receives the output of the first NC filter 5a2 toward the target ratio of 0.3. .

By performing a series of operations as described above, it is possible to perform cross-fade switching corresponding to both switching between NC characteristics realized by a single filter characteristic and switching between intermediate NC characteristics. .

[Processing procedure]

The flowcharts of FIGS. 10 and 11 show a processing procedure for realizing the crossfade switching operation as the first embodiment described above.
10 and 11, the processing procedure for realizing the cross-fade switching operation as the first embodiment is shown as a processing procedure that the DSP 5 executes based on the signal processing program 8a.
FIG. 10 shows a processing procedure when switching between NC characteristics realized by a single filter characteristic, together with a processing procedure up to a discrimination process based on a route calculation result, and FIG. 11 shows an intermediate NC characteristic. The processing procedure when switching is performed is shown.

  First, in FIG. 10, in step S101, the process waits until a new NC mode is selected. As described above, in the case of this example, the microcomputer 10 selects the NC mode based on the user operation input via the operation unit 9. The process of step S101 is a process of waiting until information representing the NC mode selected based on the user operation is input from the microcomputer 10.

  When information indicating the newly selected NC mode is input from the microcomputer 10 and a new NC mode is selected, in step S102, from the current NC characteristic to the target NC characteristic (new NC characteristic). Process to calculate the route. Since the route calculation method has already been described, further description is omitted.

In the subsequent step S103, it is determined whether or not the ratio of either one of the NC filter outputs needs to be zero in the middle of the path.
If a negative result is obtained in step S103 that it is not necessary to set the ratio of one of the NC filter outputs to 0 in the middle of the route, the process proceeds to step S104, and the target NC characteristic is obtained in the non-operating NC filter. Set the filter characteristics. That is, the filter characteristic of the non-operating NC filter 5a is set based on the filter characteristic information corresponding to the newly selected NC mode among the filter characteristic information stored as the filter characteristic information 8b in the memory 8.

In the subsequent step S105, cross-fading is performed until the output ratio of the NC filter for which the target characteristic is set is 1 and the output ratio of the other NC filter is 0. That is, the coefficient of the multiplier 5b that inputs the output of the non-operating NC filter 5a is gradually increased from 0 to 1, and the coefficient of the multiplier 5b that inputs the output of the active NC filter 5a is 1 → 0. It will gradually decrease.
When the process of step S105 is executed, the process for the crossfade switching operation according to the present example ends.

On the other hand, if a positive result is obtained in step S103 that the ratio of one of the NC filters needs to be set to 0 in the middle of the route, a series of processes shown in FIG. 11 are executed.
In FIG. 11, in step S106, the crossing is performed so that the output ratio of the NC filter on which the filter characteristic necessary only on the current NC characteristic side is set is 0, and the output ratio of the other NC filter is 1. Perform a fade. That is, the coefficient of the multiplier 5b that inputs the output of the NC filter 5a in which the filter characteristic necessary only on the current NC characteristic side is set is gradually reduced toward 0, and the output of the other NC filter 5a is input. The coefficient of the multiplying unit 5b is gradually increased toward 1.

  In the subsequent step S107, a filter characteristic for obtaining the target NC characteristic is set in the NC filter 5a having the ratio of 0. That is, the filter characteristic information for setting the filter characteristic necessary for obtaining the NC characteristic as the newly selected NC mode together with the filter characteristic set in the NC filter 5a having the ratio of 1 is set. The filter characteristic of the NC filter 5a having the ratio of 0 is set based on the filter characteristic information read from the memory 8.

In the next step S108, crossfading is performed until the newly set ratio of the output of the NC filter and the ratio of the output of the other NC filter reach the target ratio, respectively. That is, the coefficient of the multiplier 5b that inputs the output of the NC filter 5a for which the filter characteristics are newly set in step S107 is gradually increased from 0 toward the target value, and the other NC filter 5a is set. Is gradually decreased from 1 toward the target value.
Here, for confirmation, the NC mode realized by an intermediate characteristic among a plurality of filter characteristics is classified according to the filter characteristic to be set for each NC filter 5a and the ratio of each filter processing output. And is defined by The above “target ratio” refers to the ratio of each filter processing output defined for each NC mode. That is, the coefficient given as the “target value” to each multiplier 5b in step S108 gives a value as a ratio of each filter processing output defined in the NC mode newly selected in step S101. It is.
When the process of step S108 is executed, the process for the crossfade switching operation according to the present example ends.

[Summary]

According to the crossfade switching operation of the present embodiment described above, when switching to a different NC mode (NC characteristic), switching is instantaneously performed at a certain point in time as in the past. Thus, it is possible to prevent sudden switching of the NC characteristics, and to reduce the user's uncomfortable feeling accompanying the switching of the NC characteristics.

In the present embodiment, individual filter processing can be performed by a plurality of NC filters 5a, and the filter processing output from each NC filter 5a can be synthesized at a required ratio. This makes it possible to realize the NC characteristic by multiplying the filter processing outputs.
If a plurality of filter characteristics can be combined in this way, the required memory capacity can be reduced as compared with the conventional method in which one filter characteristic information is held in one-to-one correspondence for each NC characteristic. be able to. That is, effective use of storage resources can be achieved.

In the present embodiment, when a path from the current NC characteristic to the new NC characteristic is obtained, the current NC characteristic and the new NC characteristic are both a combination of a plurality of filter characteristics, and the current NC characteristic is realized. If the combination of filter characteristics required for the purpose and the combination of filter characteristics required for realizing the new NC characteristics are different from each other, the filter characteristics required only on the current NC characteristics side (the filter characteristics in the case of FIG. 8) The route is obtained on the condition that the ratio of B) is 0.
As a result, the filter characteristics can be changed during the switching operation as described above, and even when the number of NC filters 5a is two, crossfade switching between intermediate characteristics is performed appropriately. be able to. That is, this allows the number of NC filters 5a to be reduced to two.
In this way, the number of NC filters 5a can be suppressed to two, which is the minimum necessary for performing the crossfade switching, so that the processing load on the DSP 5 can be minimized. For example, even when an inexpensive DSP having a relatively low processing capability is used, the crossfade switching operation can be properly realized, and thereby an effect of reducing the device manufacturing cost can be obtained.

<Second Embodiment>

Next, a second embodiment will be described.
In the second embodiment, the selection of a new NC mode is performed not only based on a user operation but also based on automatic device selection.

FIG. 12 is a block diagram showing an internal configuration of the headphone 15 as the second embodiment. In the following description, parts that are the same as those already described are assigned the same reference numerals and description thereof is omitted.
The headphone 15 of the second embodiment is different from the headphone 1 of the first embodiment in that the function of the DSP 5 is changed. Specifically, functional operations as a sound pickup signal analysis unit 5f and an optimum NC mode selection unit 5g in the figure are added. Further, instead of the function of the filter characteristic / mix ratio control unit 5e in the first embodiment, a function as the filter characteristic / mix ratio control unit 5h is provided.

  In addition to the change in the functional operation of the DSP 5, the memory 8 stores a signal processing program 8c for realizing the operation of the second embodiment instead of the previous signal processing program 8a. The In this case, the NC effect prediction table 8d is newly stored in the memory 8.

In the headphone 15 of the second embodiment, the optimum NC mode (NC characteristic) corresponding to the external noise environment is automatically selected by the collected sound signal analysis unit 5f and the optimum NC mode selection unit 5g. To be.
Specifically, the collected sound signal analysis unit 5f performs, for example, band division by FFT (Fast Fourier Transform) or BPF (Band Pass Filter) on the collected sound data input from the A / D converter 3. To analyze the frequency characteristics of the collected sound data.
Then, the optimum NC mode selection unit 5g can set each of the headphones 15 based on the frequency characteristic analysis result by the collected sound signal analysis unit 5f and the information content of the NC effect prediction table 8d stored in the memory 8. The noise reduction effect is predicted for each NC mode, and the optimum NC mode is selected based on the prediction result.

Here, the optimum NC mode selection unit 5g predicts the noise reduction effect and the optimum NC mode selection method based on the prediction result will be described.
First, in the case of this example, as the NC effect prediction table 8d, for each NC mode (including an NC mode based on a combination of a plurality of filter characteristics) in which the headphones 15 can be set, the noise reduction characteristics (a plurality of characteristics) This information is associated with information on the amount of noise reduction with respect to frequency points. That is, the NC effect prediction table 8d is obtained by associating the attenuation curve information for each NC mode as shown in FIG. 5 with each settable NC mode.

The optimum NC mode selection unit 5g rounds out the noise reduction characteristics of each NC mode stored in the NC effect prediction table 8d with respect to the frequency characteristics of the sound collection data analyzed by the sound collection signal analysis unit 5f. Then, the optimum NC mode corresponding to the external noise environment is selected from the comparison of these values.
Here, the difference between the frequency characteristic of the collected sound data analyzed by the collected sound signal analysis unit 5f and the noise reduction characteristic stored in the NC effect prediction table 8d represents the noise reduction effect with respect to the actual noise. It will be a thing. Therefore, by obtaining the difference between the frequency characteristics of the collected sound data analyzed by the collected sound signal analysis unit 5f as described above and the noise reduction characteristics stored in the NC effect prediction table 8d for each NC mode, The noise reduction effect for each NC mode with respect to the collected noise sound is obtained as a numerical value (prediction of noise reduction effect).
Then, the optimum NC mode selection unit 5g selects the NC mode having the smallest difference value (noise reduction effect amount) thus obtained as the optimum NC mode.
It should be noted that the difference here is a difference in dB value, and in the case of a linear amplitude value, it is division.

  Here, with respect to the calculation corresponding to the prediction of the noise reduction effect, for example, a method of obtaining an energy difference for each band and obtaining the sum as a final noise reduction effect value can be cited. Further, it is desirable that the actual calculation is performed after giving an auditory characteristic curve.

  Note that the method for selecting the optimum NC mode should not be limited to the method described above, and other methods can of course be employed.

In the second embodiment, the optimum NC mode automatic selection operation performed by the collected sound signal analysis unit 5f and the optimum NC mode selection unit 5g as described above is performed using the following as a start trigger.
-When the power is turned on (when the device starts)
・ Elapsed time ・ When excessive noise is input ・ When low noise state continues

Specifically, for the start trigger when “power is on”, the microcomputer 10 issues an operation start instruction to the sound collection signal analysis unit 5 f (DSP 5) in response to an operation of a power button provided on the operation unit 9. That is, the sound collection signal analysis unit 5f starts frequency characteristic analysis for the sound collection data in response to the operation start instruction.
Further, regarding the above “elapse of the predetermined time”, “when excessive noise is input”, and “when the small noise state is continued”, the sound collection signal analysis unit 5f (DSP 5) itself determines whether or not the condition is satisfied. Specifically, with respect to the “elapse of the predetermined time”, for example, a time count is started in response to receiving an operation start instruction from the microcomputer 10 and waits until the count value reaches a predetermined value. To do. Then, in response to the count value reaching the predetermined value, frequency characteristic analysis for the sound collection data is started. At the same time, the time count value is reset, and the process waits until the time count value reaches the predetermined value again. In this way, frequency characteristic analysis is performed every time a predetermined time elapses.

In addition, when “excessive noise is input”, the level of the input sound pickup data is monitored, and frequency characteristic analysis of the sound pickup data is started when the level exceeds a predetermined level. To do.
In addition, for the “continuation of the low noise state”, it is determined whether or not a state where the level of the collected sound data to be input is equal to or lower than a predetermined level has continued for a predetermined time or more. The frequency characteristic analysis of the collected sound data is started in response to the determination that it has been continued.

  Based on the result of the frequency characteristic analysis by the collected sound signal analysis unit 5f started in this way, the optimum NC mode is selected by the optimum NC mode selection unit 5g. In other words, the optimum NC mode is selected according to the occurrence of any of the above start triggers.

  Here, when the optimum NC mode selected by the optimum NC mode selection unit 5g is the same as the current NC mode, there is no need to perform a cross-fade switching operation. For this reason, when the selected optimum NC mode is the same as the current NC mode, the optimum NC mode selection unit 5g does not give an instruction to change the NC mode to the filter characteristic / mix ratio control unit 5h, and the current NC mode. Only when the selected optimal NC mode is not the same, an instruction to change the NC mode is issued.

As the filter characteristic / mix ratio control unit 5h, the NC mode selected by the user operation based on an instruction from the microcomputer 10 like the filter characteristic / mix ratio control unit 5e in the first embodiment is used. Not only is the control for crossfade switching performed, but also the control for crossfade switching is different according to the change instruction from the optimum NC mode selection unit 5g described above.
Also in the second embodiment, the content of the crossfade switching operation itself that is executed after switching to the new NC mode is the same as in the case of the previous first embodiment. Since this is the same, a description thereof is omitted here.

  FIG. 13 is a flowchart showing a processing procedure for realizing the operation as the second embodiment described above. In FIG. 13, the processing procedure for realizing the operation as the second embodiment is shown as the processing procedure executed by the DSP 5 based on the signal processing program 8c.

In FIG. 13, first, the processing in step S201 and step S202 is either a selection of a new NC mode by a user operation or generation of the optimum NC mode automatic selection start trigger (start trigger for sound pickup signal analysis) described above. This is a process for waiting. That is, in step S201, it is determined whether or not a new NC mode has been selected by the operation. In step S201, it is determined whether information indicating the NC mode selected based on the user operation is instructed from the microcomputer 10. In step S201, if there is no instruction from the microcomputer 10 and a negative result is obtained that a new NC mode has not been selected by the operation, whether or not an analysis start trigger has occurred in step S202. Is determined. That is, it is determined whether any start trigger has occurred among the start triggers of “when the power is turned on”, “elapse of a predetermined time”, “when excessive noise is input”, or “when the low noise state continues”. Determine. In step S202, if none of the start triggers has occurred and a negative result is obtained that no analysis start trigger has occurred, the process returns to step S201.
By such loop processing from step S201 to S202, either the selection of a new NC mode by the user operation or the generation of an analysis start trigger (that is, the optimum NC mode automatic selection start trigger) is waited.

  In step S201, if there is an instruction from the microcomputer 10 and a positive result is obtained that a new NC mode is selected by the operation, the process proceeds to step S202 shown in FIG. To be done. As a result, when a new NC mode is selected by the operation, the NC mode newly selected from the current NC mode (target NC mode) as in the case of the first embodiment. The cross-fade switching operation is performed.

  In step S202, if any of the above triggers occurs and a negative result is obtained that an analysis start trigger has occurred, an optimal NC mode based on collected sound signal analysis is obtained in step S203. Make a selection. That is, as described above, the frequency characteristics of the collected sound data input from the A / D converter 3 are analyzed, and the analyzed frequency characteristics and the information content of the NC effect prediction table 8d in the memory 8 are analyzed. In accordance with the prediction result of the noise reduction effect for each NC mode, the optimum NC mode is selected according to the external noise environment.

  In a succeeding step S204, it is determined whether or not the optimum NC mode is different from the current NC mode. If a negative result is obtained in step S204 that the optimal NC mode is the same as the current NC mode and the optimal NC mode is not different from the current NC mode, the process returns to step S201. As a result, when the optimum NC mode automatically selected matches the current NC mode, the crossfade switching operation is not executed.

On the other hand, if a positive result is obtained in step S204 that the optimum NC mode is different from the current NC mode, the process proceeds to step S102 in FIG. Thus, when the automatically selected optimum NC mode is different from the current NC mode, the automatically selected optimum NC mode is set as the target NC mode (target NC characteristic), and the crossfade switching operation to the target NC mode is performed. Will be executed.

<Third Embodiment>

The third embodiment relates to a sound reproduction system including a headphone device and a signal processing device such as an audio player in which the headphone device can be attached and detached, and a signal processing system for noise canceling is provided. It is provided not on the headphone device side but on the signal processing device side. In other words, the sound reproduction system is composed of an audio player (30) having a noise canceling function and a (normal) headphone (20) having no noise canceling function.

FIG. 14 is a block diagram showing the internal configuration of the audio player 30 and the internal configuration of the headphones 20 as a diagram for explaining the configuration of the sound reproduction system according to the third embodiment.
First, the headphone 20 in this case is provided with a microphone MIC, a microphone output terminal TMout, an audio input terminal TAin, and a driver DRV. The collected sound signal obtained by the microphone MIC is supplied to the microphone output terminal TMout. The audio input terminal TAin is connected to the driver DRV.

  On the other hand, as can be seen from the comparison with FIG. 12, the audio player 30 has an audio signal having the same configuration as the audio signal processing system for noise cancellation included in the headphone 15 of the second embodiment. A processing system is provided. Specifically, the headphone 15 includes a microphone amplifier 2, an A / D converter 3, a DSP 5 (and memory 8), a D / A converter 6, and a power amplifier 7. Since the operation of each part of the audio signal processing system for noise canceling is the same as that already described, a description thereof will be omitted.

  However, in this case, the microphone MIC 2 is supplied with a sound collection signal from the microphone MIC via the microphone output terminal TMout → the microphone input terminal TMin provided on the audio player 30 side. The output signal of the power amplifier 7 is supplied to the driver DRV via the audio output terminal TMout provided on the audio player 30 side → the audio input terminal TAin described above.

  The microphone output terminal TMout, the audio input terminal TAin, and each terminal T of the microphone input terminal TMin and the audio output terminal TMout are connected to the [microphone output terminal TMout− when the headphones 20 are connected to the audio player 30. The microphone input terminal TMin] and [audio output terminal TMout−audio input terminal TAin] are formed on the headphone 20 side and the audio player 30 side so as to contact each other.

The audio player 30 includes a storage unit 31 and a reproduction processing unit 32 as a reproduction system for audio data.
The storage unit 31 is used for storing various data including audio data. As a specific configuration, for example, data may be written (recorded) / read to / from a solid-state memory such as a flash memory, or may be configured by an HDD (Hard Disk Drive), for example.
Also, not a built-in recording medium, but a portable recording medium, for example, a memory card incorporating a solid-state memory, an optical disk such as a CD (Compact Disc) or a DVD (Digital Versatile Disc), a magneto-optical disk, a hologram memory, or the like. It can also be configured as a drive device corresponding to the above.
Of course, both a built-in type memory such as a solid-state memory and an HDD, and a drive device for a portable recording medium may be mounted.
The storage unit 31 writes / reads audio data and other various data based on the control of the microcomputer 33 described later.

Here, it is assumed that the storage unit 31 stores audio data in a state of being compressed and encoded by a predetermined audio compression encoding method. The compressed audio data read by the storage unit 31 is supplied to the reproduction processing unit 32. The reproduction processing unit 32 performs predetermined reproduction processing (decoding processing) such as expansion processing on the supplied compressed audio data based on the control of the microcomputer 33.
The audio data reproduced by the reproduction processing unit 32 is supplied to the DSP 5 as audio data for listening.

The microcomputer 33 performs overall control of the audio player 30.
For example, data write / read control with respect to the storage unit 31 is performed. The storage unit 31 and the playback processing unit 32 are also controlled to perform playback start / stop control of audio data.
An operation unit 34 is connected to the microcomputer 33 and performs calculation based on operation input information based on user operation input supplied from the operation unit 34 and operation control of each unit. Thus, an operation corresponding to the user operation can be obtained in the audio player 30.
Here, the operation unit 34 is provided with at least a power button and a selection button for performing an NC mode selection operation, similar to the operation unit 9 provided in the headphone 15 of the second embodiment. It is done. The microcomputer 33 in this case also has a DSP 5 (sound pickup) in response to the operation input information for power-on being supplied in response to the operation of the power button, as in the microcomputer 10. An operation start instruction is given to the signal analysis unit 5f). Further, based on the operation input information supplied from the operation unit 9 in response to the operation of the selection button, the NC mode to be newly set is selected, and information indicating the selected NC mode is displayed in the DSP 5 (filter characteristics / The mixing ratio control unit 5h) is instructed.

  A display unit 35 is connected to the microcomputer 33. The display unit 35 is a display device such as a liquid crystal display or an organic EL display, for example, and displays required information in response to an instruction from the microcomputer 33.

Also with the configuration shown in FIG. 14, the automatic selection operation and the cross-fade switching operation in the optimum NC mode similar to those described in the second embodiment can be performed. Further, by changing the signal processing program 8c stored in the memory 8 to the signal processing program 8a shown in FIG. 4, the same crossfade switching operation as that in the first embodiment is performed. You can also

<Modification>

Although the embodiments of the present invention have been described above, the present invention should not be limited to the specific examples described above.
For example, in the description so far, a case where the number of channels (including channels) of an audio signal (including a collected sound signal) is only 1 ch has been shown, but in the present invention, sound reproduction is performed for audio signals of a plurality of channels. The present invention can also be suitably applied when performing the above.

  In the description so far, only the case where the FF method is adopted as the noise canceling method has been exemplified, but the present invention can also be suitably applied to the case where the FB method is adopted. When the FB method is adopted, the arrangement position of the microphone MIC is different from that when the FF method is adopted. Specifically, the sound is provided inside the housing part so as to collect sound in the housing part, that is, noise sound and output sound from the driver DRV (see FIG. 1). Other configurations may be the same as those shown in FIG. 4, FIG. 12, and FIG.

  However, as described in the description of the basic concept at the beginning, in the FB method, audio that is added to the feedback loop and listened to by the user as the noise canceling filter processing is performed in the feedback loop. There is a risk that the sound quality of the signal (listening audio signal) may deteriorate. For this purpose, as shown in FIG. 1B, an equalizer is provided for performing equalizing processing for preventing deterioration of sound quality for audio data for listening. This equalizer is realized by digital signal processing of the DSP 5. For example, in the case of FIG. 4 and FIG. 12, the audio data for listening input from the A / D converter 3 is prevented from being deteriorated. What is necessary is just to perform an equalizing process. Alternatively, in the case of FIG. 14, the listening audio data input from the reproduction processing unit 32 may be subjected to equalizing processing for preventing sound quality deterioration.

Here, in order to appropriately prevent the deterioration of the message, the equalizer characteristics of the equalizer should be variably set according to the set NC mode. That is, since the sound quality deterioration mode varies depending on the NC characteristics of the set NC mode, the equalizing characteristics of the equalizer should be set in accordance with the NC characteristics of the set NC mode.
In consideration of this point, when the FB method is adopted, it is conceivable that the equalizing characteristic of the equalizer (for example, a filter characteristic such as an FIR filter) is switched in accordance with switching of the NC mode.

  As described above, when the equalizing characteristic of the equalizer for preventing the deterioration of sound quality is switched, there is a possibility that the user feels uncomfortable with the sound quality change at the switching point, as in the case of switching the NC mode. Therefore, the switching operation of the equalizer equalizing characteristic of the equalizer can also be performed as a crossfade switching operation similar to the switching of the NC mode. In this case, the operation is the same as the NC mode cross-fade switching operation described above except that the filter characteristic is set from the NC filter 5a to the equalizer. In other words, as a functional block of the DSP 5, a plurality of equalizers that receive listening audio data and individually perform equalizing processing and equalizing outputs (filter processing outputs) from these equalizers are combined at a set combining ratio. A plurality of multipliers and an adder for adding the outputs of the multipliers, and the current NC mode is set by setting (controlling) the equalizing characteristics (filter characteristics) of the plurality of equalizers and the coefficients given to the plurality of multipliers. A filter characteristic / mix ratio control unit that performs cross-fade switching control from the corresponding equalizing characteristic to the equalizing characteristic corresponding to the new NC mode may be provided.

Further, in the case of adopting the FB method, considering that the optimum NC mode is selected as in the second embodiment, in the case of the FB method, a microphone is formed along with the formation of a feedback loop. The collected sound signal from the MIC includes not only a noise component but also an audio signal component for listening. For this reason, when the audio signal for listening is being reproduced, the collected sound signal analysis unit 5f may not be able to correctly perform the frequency characteristic analysis on the noise component. That is, there is a possibility that the optimum NC mode cannot be correctly selected.
In addition, in the case of the FB method, in the state where the feedback loop is turned on, the sound collection data input to the sound collection signal analysis unit 5f is given signal characteristics for noise canceling. ing. That is, the noise component is reduced. In this respect as well, there is a possibility that the optimum NC mode cannot be correctly selected.
Therefore, when the optimum NC mode is selected when the FB method is adopted, the adder 5d does not perform the operation of adding the audio data for listening to the feedback loop, and for example, inputs the collected sound data to the NC filter 5a. And the feedback loop is turned off (ie, only the noise component is collected by the microphone MIC), and the frequency characteristic analysis is performed by the collected sound signal analysis unit 5f. As a result, the optimum NC mode can be selected more accurately corresponding to the case where the FB method is adopted.

In the above description, for the sake of simplicity, the filter characteristic information 8b in the memory 8 is assumed to hold three pieces of filter characteristic information. Of course, the number of filter characteristic information held should be limited to this. It can also be 2 or 4 or more.
FIG. 15 illustrates, as an example, the relationship between each filter characteristic when the number of filter characteristic information held is six.
FIG. 15 also shows an example of paths between the NC characteristics when the number of NC filters 5a is two. For example, in the case of switching from an intermediate NC characteristic between the filter characteristic A and the filter characteristic F indicated by x1 to an intermediate NC characteristic between the filter characteristic A and the filter characteristic C indicated by x2, in this case, However, the route to x2 is calculated on the condition that the ratio of the required filter characteristic (filter characteristic F) is 0 only on the NC characteristic side before switching. Further, for example, even when switching from the NC characteristic as x2 to an intermediate NC characteristic between the filter characteristic C and the filter characteristic F indicated by x3, similarly, only on the NC characteristic side before the switching is performed. It is shown that the route to the above x3 is calculated on the condition that the required filter characteristic (filter characteristic A) ratio passes through zero.

  In the description so far, the case where the number of NC filters is two in consideration of the performance and processing load of the DSP 5 is exemplified, but it is needless to say that the number of NC filters may be three or more. As understood from the above description, when the number of NC filters is two, the ratio of one NC filter processing output is set to 0 during the cross-fade switching, and the NC filter side of which the ratio is set to 0 However, when there are three or more NC filters, it is not necessary to replace the filter characteristics during the crossfade switching.

  In FIG. 16, as an example, a configuration example in which three NC filters are provided is shown. In this case, a first NC filter 5a1, a second NC filter 5a2, and a third NC filter 5a3 for individually inputting sound collection data are provided, and the first multiplier 5b1 and the second NC filter 5a2 for inputting the output of the first NC filter 5a1 are provided. A second multiplier 5b2 for inputting the output, a third multiplier 5b3 for inputting the output of the third NC filter 5a3, and an adder 5c for adding the outputs of the first to third multipliers 5b are provided.

Here, as shown in FIG. 16, the filter characteristic A is set in the first NC filter 5a1, the filter characteristic B is set in the second NC filter 5a2, and the filter characteristic C is set in the third NC filter 5a3. Suppose that
FIG. 17 illustrates the relationship between the filter characteristics A to C set in each NC filter 5a in this way. For example, in the state where the relationship between the filter characteristics shown in FIG. 17 is obtained, the filter characteristic A and the filter characteristic C are obtained from the NC characteristic intermediate between the filter characteristic A and the filter characteristic B as shown in the figure. It is assumed that the state should be switched to the intermediate NC characteristic. When the number of the NC filters 5a exemplified above is two, as shown by the white circles in the figure, the filter characteristic B has a ratio of 0 and the filter characteristic A has a ratio of 1 so as to pass. When the number of NC filters 5a is three, the mixing ratio of the three types of filters is changed, for example, as shown by the colored circles in the figure. The NC characteristic can be changed linearly toward. That is, the path can be calculated without having to pass through a point where the ratio of the required filter characteristic (in this case, the filter characteristic B) is 0 only on the NC characteristic side before switching. Therefore, it is not necessary to change the filter characteristics during the crossfade switching.

  In the description so far, the case where both the NC mode realized by one filter characteristic and the NC mode realized by a combination of a plurality of filter characteristics coexist as the NC mode is exemplified. When only the NC mode that can be realized by the filter characteristics is set, the crossfade switching operation can be performed. In that case, it is not necessary to calculate the route as shown in FIG. 10 (S102) and to determine whether the ratio of one of the NC filter outputs needs to be zero in the middle of the route. Yes, in response to the fact that a new NC mode should be set, the filter characteristics corresponding to the new NC mode are set for the non-operating NC filter 5a, and then the ratio of the filter processing output on the movable side Is gradually decreased from 1 to 0, and the ratio of the filter processing output on the non-operating side is gradually increased from 0 to 1, so that the synthesis ratio may be changed.

  In the description so far, the case where the NC filter that gives the signal characteristics for noise canceling to the collected sound signal is configured by a digital filter, but the NC filter can also be configured by an analog filter. .

  In the above description, the case where the signal processing device of the present invention is configured as a headphone device or an audio player has been exemplified. However, as the signal processing device of the present invention, for example, a mobile phone having a noise canceling function It can also be implemented as other device forms such as a headset.

It is a figure which shows the model example about the noise cancellation system of the headphone apparatus by a feedback system. It is a Bode diagram which shows the characteristic about the noise canceling system shown in FIG. It is a figure which shows the model example about the noise canceling system of the headphone apparatus by a feedforward system. It is the block diagram which showed the internal structure of the signal processing apparatus of 1st Embodiment. It is the figure which illustrated the noise reduction characteristic for every NC mode. As a diagram for explaining the cross-fade switching operation of the first embodiment, it is a diagram showing an operation example corresponding to the case where the filter characteristics and the NC mode correspond one-to-one. It is the figure which showed the example of the crossfade characteristic. As a diagram for explaining a cross-fade switching operation corresponding to switching between intermediate NC characteristics by a combination of a plurality of filter characteristics, the relationship between the NC characteristics before switching and the NC characteristics after switching is shown. FIG. It is the figure which showed the example of an actual operation | movement as a figure for demonstrating the crossfade switching operation | movement performed corresponding to switching between the intermediate | middle NC characteristics by the combination of a some filter characteristic. It is the flowchart which showed the process sequence for implement | achieving the crossfade switching operation | movement as 1st Embodiment. Similarly, it is the flowchart which showed the process sequence for implement | achieving the crossfade switching operation | movement as 1st Embodiment. It is the block diagram which showed the internal structure of the signal processing apparatus of 2nd Embodiment. It is the flowchart which showed the process sequence for implement | achieving the operation | movement (mainly automatic selection operation | movement of an optimal NC mode) as 2nd Embodiment. It is the figure which showed the structure of the sound reproduction system comprised including the signal processing apparatus and headphone apparatus as 3rd Embodiment. It is the figure which illustrated the path | route between each NC characteristic implement | achieved by the relationship of each filter characteristic when the holding | maintenance number of filter characteristic information is six, and the combination of several filter characteristics. It is the figure which showed the structural example in the case of providing three NC filters. It is the figure which illustrated the relationship of the filter characteristic set to each NC filter of FIG.

Explanation of symbols

  1,15,20 Headphone, 2 Microphone amplifier, 3,4 A / D converter, 5 DSP, 5a NC filter, 5b Multiplier, 5c, 5d Adder, 5e, 5h Filter characteristics / Mix ratio controller, 5f Sound signal analysis unit, 5g optimum NC mode selection unit, 6 D / A converter, 7 power amplifier, 8 memory, 8a, 8c signal processing program, 8b filter characteristic information, 8d NC effect prediction table, 9 operation unit, 10, 33 microcomputer, 30 audio player, 31 storage unit, 32 playback processing unit, 34 operation unit, 35 display unit, MIC microphone, DRV driver, TAin audio input terminal, TMout microphone output terminal, TAout audio output terminal, TMin microphone input Terminal

Claims (16)

A plurality of filter processing means each for inputting a collected sound signal obtained based on a sound collecting operation by a microphone and individually performing a filtering process to give different signal characteristics to the collected sound signal;
Synthesizing means for synthesizing filter processing outputs from the plurality of filter processing means according to a set synthesis ratio;
A signal processing apparatus comprising: a control unit that changes a synthesis ratio by the synthesis unit in a time-varying manner in response to a state in which a signal characteristic to be applied to the sound pickup signal is to be switched. The signal processing device according to claim 1,
Each of the plurality of filter processing means performs a filter process for giving a signal characteristic for noise canceling to the collected sound signal,
The control means includes
The synthesis ratio is changed in accordance with the state in which the noise canceling mode should be switched. The signal processing device according to claim 2,
The plurality of filter processing means are realized as one function of the digital signal processor, and the filter processing characteristics of each filter processing means can be variably set. The signal processing device according to claim 3,
The control means includes
At least one filter processing means is set with a filter processing characteristic for realizing a new noise canceling mode that should be newly set when the noise canceling mode is switched, and the filter processing characteristic The composition ratio is changed so that the ratio of the filter processing output of the filter processing means for which is set to gradually increases with time. The signal processing device according to claim 4,
The plurality of filter processing means are two of a first filter processing means and a second filter processing means. The signal processing device according to claim 5,
The control means includes
In response to the state in which the noise canceling mode should be changed, the first and second are changed when changing from the current noise canceling mode that has been set to the new noise canceling to be newly set. The filter processing characteristics to be set in the filter processing means and the composition ratio to be sequentially set in each filter processing output are obtained by calculation,
As a result of the calculation, when it is not necessary to set the ratio of the filter processing output of either the first or second filter processing means to 0 during the change to the new noise canceling mode, the first 1, the composition ratio is changed so that the ratio of the filter processing output of the second filter processing means gradually changes toward the ratio obtained by the above calculation,
As a result of the calculation, when it is necessary to set the ratio of the filter processing output of either the first or second filter processing means to 0 during the change to the new noise canceling mode, the calculation According to the result, the synthesis ratio is changed so that the ratio of the filter processing output of one filter processing means is gradually increased toward 1 and the ratio of the filter processing output of the other filter processing means is gradually decreased toward 0. A ratio obtained by calculating the ratio of the filter processing output of the other filter processing means after setting a new filter processing characteristic based on the calculation result in the other filter processing means having a ratio of 0. And gradually increase the ratio of the filter processing output of the one filter processing means toward the ratio obtained by the above calculation. Changing the synthesis ratio so as to reduce the. The signal processing device according to claim 5,
The noise canceling mode and the filtering characteristic are assumed to correspond one-to-one.
The control means includes
In response to the fact that the noise canceling mode should be switched, the filter processing characteristics for realizing the current noise canceling mode set up to that time of the first or second filter processing means are as follows. A filter processing characteristic for realizing a new noise canceling mode to be newly set is set for a filter processing unit on the non-operating side, which is different from the set filter processing unit on the operating side. The composition ratio is such that the ratio of the filter processing output of the operating side filter processing means is gradually increased toward 1 and the ratio of the filter processing output of the operating side filter processing means is gradually decreased toward 0. To change. The signal processing device according to claim 1,
The control means includes
The synthesis ratio is changed so that the ratio given to the filter processing output is constantly changed with respect to time. The signal processing device according to claim 1,
The control means includes
The synthesis ratio is changed so that the ratio given to the filter processing output changes non-constantly with respect to time. The signal processing device according to claim 1,
The control means includes
The composition ratio is changed by changing the ratio change mode with respect to time depending on whether the ratio given to the filter processing output is increased or decreased. The signal processing device according to claim 1,
The control means includes
When increasing the ratio given to the filter processing output, the ratio change amount is gradually decreased with time, and when decreasing the ratio given to the filter processing output, the ratio is gradually increased with time. The synthesis ratio is changed so as to increase the amount of change. The signal processing device according to claim 2,
Further comprising mode selection means for selecting the noise canceling mode based on a user operation,
The control means includes
The synthesis ratio is changed in response to selection of a new noise canceling mode by the mode selection means. The signal processing device according to claim 2,
Further comprising mode automatic selection means for automatically selecting the noise canceling mode based on the collected sound signal,
The control means includes
The synthesis ratio is changed in response to selection of a new noise canceling mode by the mode automatic selection means. Filtering steps for providing different signal characteristics to the collected sound signals by inputting the collected sound signals obtained based on the sound collecting operation by the microphone and individually performing the filtering process;
A synthesis step for synthesizing the respective filter processing outputs of the filter processing step by changing the synthesis ratio in a time-varying manner in response to the state in which the signal characteristics to be given to the sound pickup signal are to be switched. A signal processing method provided. A plurality of filter processing means each for inputting a collected sound signal obtained based on a sound collecting operation by a microphone and individually performing a filtering process to give different signal characteristics to the collected sound signal;
A signal processing apparatus comprising: combining means for combining the filter processing outputs from the plurality of filter processing means at a set combining ratio. Filtering steps for providing different signal characteristics to the collected sound signals by inputting the collected sound signals obtained based on the sound collecting operation by the microphone and individually performing the filtering process;
And a synthesis step of synthesizing the respective filter processing outputs of the filter processing step according to a set synthesis ratio.

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