JP2011040831A - Headphone and method for canceling digital noise - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a headphone and a method for canceling digital noise, enabling a user to listen only musical by canceling surrounding noise and capable of improving an S/N ratio by eliminating the influence of inside noise even if environmental noise is small. <P>SOLUTION: The digital noise canceling headphone has a microphone, an A/D converter, a digital signal processing device, a D/A converter, a mixer and a speaker, wherein the digital signal processing device has a cancellation signal generating means, a level detecting means, a level determining means and a cancellation signal level adjusting means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a digital noise canceling headphone and a digital noise canceling method. More specifically, the present invention is a digital which can improve the S / N ratio by eliminating the influence of internal noise even when environmental noise is small. The present invention relates to a noise canceling phone and a digital noise canceling method.

There is known a noise-canceling headphone that can listen to reproduced music while canceling environmental noise with a canceling sound (see, for example, Patent Document 1).
As shown in Patent Document 1, a conventional noise canceling headphone converts ambient noise collected by a microphone unit attached to a headphone housing into an electrical signal, and passes through the headphone housing based on this environmental noise. Then, a cancel signal that cancels noise heard by the user's ear is generated, and the cancel signal is output from the headphone speaker unit together with music to be reproduced.
Japanese Patent No. 2562708

In such conventional noise canceling headphones, internal noise generated from a circuit that generates a cancel signal is mixed with a music signal together with the cancel signal and output from a speaker.
When the environmental noise is relatively large, the internal noise will not be annoying, but if the environmental noise is canceled and reduced by the cancellation signal, the generated internal noise will be relatively large regardless of the magnitude of the environmental noise. It becomes a state that can be heard by the person.

  The relationship between environmental noise and internal noise will be described using a conventional digital noise canceling headphone as an example. FIG. 5 is an example of functional blocks in a conventional digital noise canceling headphone. The digital noise canceling headphone 10 includes a microphone 11 that is a microphone unit that converts environmental noise into an electric signal, an amplifier 12 that is a microphone amplifier, and an A / D (analog / digital converter) 13 that converts the electric signal into a digital signal. A digital signal processing device (hereinafter referred to as “DSP”) 14 that performs signal processing to generate and output a cancel signal, and a D / A 15 (digital / analog conversion) that converts the cancel signal output from the DSP 14 into an electrical signal A mixer 16 that mixes and outputs the music signal supplied from the music source M and the electrical signal output from the D / A 15, an amplifier 17 that is an amplifier for the mixed signal, and the mixed signal And a speaker 18 that is a speaker unit that outputs

  Here, the transfer function of the microphone 11 is “M”, the combined transfer function of the amplifier 12, A / D 13, DSP 14, D / A 15 and mixer 16 is “PCB”, the transfer function of the amplifier 17 is “AMP”, The transfer function is “SP”. Further, the environmental noise collected by the microphone 11 is N (t). Then, the cancel signal output from the speaker 18 can be expressed by (M × PCB × AMP × SP × N) (t).

  Internal noise is generated individually in each block constituting the digital noise canceling headphones. That is, the transfer function of each block is multiplied by the internal noise of each block, and can be expressed as (M · N1) × (PCB · N2) × (AMP · N3) × (SP · N4). Here, N1, N2, N3, and N4 indicate internal noise in each block. The internal noise of each block is put together, and each block has an ideal state with no internal noise, and Nin is an equivalent internal noise assuming that the internal noise synthesized from the internal noise of each block is on the input side.

  The environmental noise N (t) is heard by the user's ear after being attenuated by a headphone housing (not shown). Here, if the sound insulation characteristic of the headphone housing is H, the environmental noise audible to the user in the noise canceling headphone 10 is {(H × N) (t)} + {(M × PCB × AMP × SP × N). (T)} + {(M × PCB × AMP × SP × Nin) (t)}.

The first term of the above formula is the environmental noise attenuated by the sound insulation characteristics of the headphone housing, and indicates the attenuated environmental noise heard by the user. The relationship between the environmental noise Ne, the canceled environmental noise Nc, and the internal noise Nin is as shown in FIG. That is, if the environmental noise Ne is sufficiently larger than the internal noise Nin, the environmental noise Nc also becomes relatively large with respect to the internal noise Nin. Therefore, in the sound output from the speaker 18 by mixing the cancel signal and the music signal, The user does not hear any internal noise and can listen to music in a suitable situation.
However, as shown in FIG. 6B, when the environmental noise Ne is small, the canceled environmental noise Nc may be smaller than the internal noise Nin. As described above, when the noise canceling headphones 10 are used in a relatively quiet environment, the user can hear the internal noise Nin in the sound output from the speaker 18 by mixing the cancel signal and the music signal. That is, the user can hear a sound like so-called white noise such as “sher” and feel uncomfortable.

  The present invention has been made in view of the above problems, and even in an environment where the environmental noise is relatively small, the internal noise is effectively prevented from being heard by the user while the environmental noise is effectively muted. An object of the present invention is to provide a digital noise canceling phone and a digital noise canceling method that can change the mixing level of the cancel signal according to the input level of the environmental noise and obtain an output with less noise.

  The present invention relates to a microphone that converts environmental noise into an electric signal, an A / D converter that converts the electric signal into digital, and a digital signal that generates and outputs a cancel signal that cancels the environmental noise based on the converted digital signal. A processing device, a D / A converter that converts a cancel signal into an electrical signal, a mixer that mixes and outputs the cancel signal and an externally input music signal, and an electrical signal that is input from the mixer is output as an audible signal A digital noise canceling headphone, wherein the digital signal processing device generates a cancel signal, a cancel signal generating means, a level detecting means for detecting the level of environmental noise, and a detection result of the level means, Level determining means for determining the attenuation level of the cancel signal, based on the attenuation level, Cancellation signal level adjusting means for outputting to attenuate the signal, and characterized mainly in that it has a.

  According to another aspect of the present invention, in the noise canceling headphones, the level determining means determines a predetermined coefficient that predefines an attenuation level when the environmental noise is smaller than a reference level.

  Another aspect of the present invention is characterized in that, in the noise canceling headphones, the level determining means determines a coefficient relative to the level of the environmental noise when the environmental noise is smaller than a reference level.

  Another aspect of the present invention is characterized in that, in the noise canceling headphones, the level determining means determines the coefficient stepwise with respect to the level of the environmental noise when the environmental noise is smaller than the reference level. To do.

  Another embodiment of the present invention generates a microphone that converts environmental noise into an electric signal, an A / D converter that converts the electric signal into digital, and a cancel signal that cancels the environmental noise based on the converted digital signal. Digital signal processing device for output, D / A converter for converting cancel signal to electric signal, mixer for mixing and outputting cancel signal and externally input music signal, electric signal input from mixer as audible signal A digital signal processing device that generates a cancellation signal, a level detection unit that detects a level of environmental noise, and a cancellation signal attenuation level according to a detection result of the level unit. Level determining means to determine, cancellation signal that attenuates and outputs the cancellation signal based on the attenuation level A digital noise canceling method using digital noise canceling headphones having a bell adjusting means, wherein the cancel signal generating means generates a cancel signal based on the environmental noise, and the level detecting means detects the level of the environmental noise. The level determining means determines the cancellation signal attenuation level according to the input level detected by the level means; and the cancellation signal level adjusting means attenuates the cancellation signal using the attenuation level determined in the above step. And outputting the output.

  According to another aspect of the present invention, in the noise canceling method, the step of determining the attenuation level in the level determining unit is a predetermined value that predetermines the attenuation level when the level detected by the level detecting unit is smaller than a reference level. It is the step which determines to the coefficient of this.

  According to another aspect of the present invention, in the noise canceling method, the step of determining the attenuation level in the level determining unit is relative to the level of the environmental noise when the level detected by the level detecting unit is smaller than the reference level. It is a step of determining a coefficient to be performed.

  According to another aspect of the present invention, in the noise canceling method, the step of determining the attenuation level in the level determining unit is performed when the level detected by the level detecting unit is smaller than a reference level with respect to the level of environmental noise. Thus, the coefficient is determined step by step.

  According to the present invention, a normal silencing effect can be obtained when the environmental noise is large, and a silent feeling without noise can be obtained when the environmental noise is small, and a silent feeling can be obtained regardless of the level of the environmental noise. Digital noise canceling headphones and noise canceling method can be obtained.

It is a functional block diagram which shows the Example of the digital noise cancellation headphones concerning this invention. It is a block diagram which shows the example of DSP with which the digital noise cancellation headphones concerning this invention are provided. It is a flowchart which shows the example of the digital noise cancellation method concerning this invention. It is a figure which shows the example of the relationship between the environmental noise Ne and the internal noise Nin in the digital noise cancellation headphones concerning this invention. It is a functional block diagram which shows the example of the conventional digital noise cancellation headphones. It is a figure which shows the example of the relationship between the environmental noise Ne and the internal noise Nin in the conventional digital noise cancellation headphones.

  An example of an embodiment of a digital noise canceling headphone and a noise canceling method according to the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram showing an example of a digital noise canceling headphone according to the present invention. In FIG. 1, a digital noise canceling headphone 100 includes a microphone 110 that is a microphone unit that converts environmental noise into an electric signal, an amplifier 120 that is an amplifier that amplifies a signal input from the microphone 110, and an electric signal as a digital signal. A / D 130 for conversion, DSP 140 for performing signal processing for generating and outputting a cancel signal, D / A 150 for converting the cancel signal output from DSP 140 into an electrical signal, and a music signal supplied from music source M A mixer 160 that mixes and outputs a cancel signal supplied from the D / A 150, an amplifier 170 that is a mixed signal amplifier that drives the speaker 180, and a speaker that is a speaker unit that outputs the mixed signal. 180.

  The digital noise canceling headphones according to the present invention are characterized by a functional configuration provided in a digital signal processing device (DSP). Therefore, an example of a DSP used in the present invention will be mainly described as an embodiment of the digital noise canceling headphones according to the present invention. FIG. 2 is a functional block diagram showing an example of a DSP included in the digital noise cancellation headphones according to the present invention. The functions of the DSP 140 shown in FIG. 2 are realized by software that operates using hardware resources of the DSP 140.

In FIG. 2, the DSP 140 includes a cancel signal generation unit 141, a level detection unit 142, a level determination unit 143, and a cancel signal level adjustment unit 144.
The cancel signal generation unit 141 is a unit that receives an environmental noise signal collected by a microphone (not shown) and converted into a digital signal by the A / D 13, and generates and outputs a cancellation signal based on the environmental noise signal.

  The level detection means 142 is a means for calculating an effective value or an average value (hereinafter referred to as “effective value or the like”) of the environmental noise signal input from the A / D 13. The level determining unit 143 is a unit that determines a coefficient for changing the output level of the cancel signal in accordance with the effective value calculated by the level detecting unit 142.

  The cancel signal level adjusting unit 144 is a unit that attenuates and outputs the cancel signal input from the cancel signal generating unit 141 using the coefficient determined by the level determining unit 143.

  Next, an example of a digital noise cancellation processing method according to the present embodiment that is performed using the DSP 140 will be described. FIG. 3 is a flowchart illustrating an example of digital noise cancellation processing according to the present embodiment. When the environmental noise signal input from the microphone is converted into a digital signal by the A / D 13 and input to the level detection unit 142, the level detection unit 142 calculates an effective value of the environmental noise (S10). The calculation process for calculating the effective value and the like is a process realized by a known technique. Further, in the digital noise canceling headphones according to the present invention, the effects described later can be obtained in the same manner regardless of whether the calculation process in the level detection unit 142 is an effective value calculation process or an average value calculation process. it can.

  In addition, it is desirable to calculate the effective value in a relatively long time. This calculation time is determined by the number of ambient noise captured data converted into a digital signal and the sampling time. If this time is shortened, it reacts sensitively to environmental noise, and conversely, if the time is long, it becomes insensitive. A suitable standard is about 20 ms.

  Next, the level determination means 143 performs processing for determining the level of the calculated effective value or the like (S20). This level determination process (S20) is a process for comparing a predetermined reference value with a level such as an effective value. In this level determination process (S20), if the level such as the effective value is larger than the reference value, the environmental noise is relatively large. Therefore, it is not necessary to attenuate the cancellation signal to attenuate the output level of the internal noise, which will be described later. The attenuation coefficient in the coefficient determination process (S30) is not set.

  In the level determination process (S20), a predetermined reference value is compared with a level such as an effective value. If the level such as the effective value is smaller than the reference value, it can be determined that the environmental noise is relatively small. Therefore, an attenuation coefficient for attenuating the output of the internal noise is set in the coefficient determination process (S30). The reference value may be a value that exhibits the effect exhibited by the digital noise canceling headphones according to the present invention, and may be variable according to the use environment.

In the coefficient determination process (S30), the coefficient may be uniquely determined when the level of the effective value or the like is larger than the reference value.
Further, the effective value or the like is determined by dividing the level within a predetermined range, a coefficient corresponding to the level range is defined, stored in a memory (not shown), and the determined effective value or the like is determined. The coefficient corresponding to the level may be read out from the memory and determined.
Further, the coefficient may be changed steplessly according to the level of the effective value or the like so that the predetermined value is uniquely determined relative to the level of the effective value or the like determined by the level determining means 143.

Using the coefficient determined by any one of the methods described above, attenuation output processing for attenuating the cancellation signal output from the cancellation signal generation unit 141 and outputting it to the D / A 15 is performed (S40).
The attenuation output process (S40) is a process of varying the level of the cancel signal output from the speaker by multiplying the coefficient determined in the coefficient determination process (S30) by the output of the cancel signal generation unit 141. After this processing, the cancel signal output from the cancel signal level adjusting means 144 is converted into an analog signal by the D / A 15 and mixed with the musical sound signal input from the music source M by the mixer and output from the speaker.

The effect of the digital noise cancellation method according to the present invention described above will be described with reference to FIG. FIG. 4 is a diagram showing the relationship between the magnitude of the music signal M input to the mixer, the environmental noise Ne, the internal noise Nin, and the canceled environmental noise Nc.
FIG. 4A shows the relationship between the music signal M and the internal noise Nin when the environmental noise Ne is smaller than the internal noise Ni in the conventional noise cancellation method. As shown in FIG. 4A, the canceled environmental noise Nc is lower than the music signal M, but when the internal noise Nin is mixed with the music signal M and output, the music signal M and the internal noise Nin are output. Therefore, the S / N ratio becomes small.

  FIG. 4B shows the relationship between the music signal M and the internal noise Nin when the environmental noise Ne is smaller than the internal noise Ni in the noise canceling method according to the present invention. As shown in FIG. 4B, when the environmental noise is low compared to a predetermined reference value, if the level of the cancel signal is attenuated by the attenuation output process (S40 in FIG. 3) and then output, the music signal M On the other hand, the level of the internal noise Ni is relatively lowered, and the S / N ratio by the music signal M and the internal noise Ni is larger than that of the conventional one (FIG. 4A).

  As described above, according to the digital noise canceling headphones and the digital noise canceling method according to the present invention, when the environmental noise is relatively small, the output of the cancel signal is attenuated so that the internal noise becomes more harsh than the environmental noise. Can be prevented. Further, according to the digital noise canceling headphone according to the present invention, when the environmental noise is relatively small, the magnitude of the internal noise with respect to the music signal is reduced by attenuating the output of the cancel signal before mixing with the music signal. can do. As a result, the S / N ratio is improved, and the user can listen to high-quality music.

  The present invention is also applicable to noise cancellation processing in various acoustic systems that reproduce and output music signals, such as concert halls and car audio.

140 Digital Signal Processing Device 141 Cancel Signal Generation Unit 142 Level Detection Unit 143 Level Determination Unit 144 Cancel Signal Level Adjustment Unit

Claims (8)

A microphone that converts environmental noise into an electrical signal, an A / D converter that digitally converts the electrical signal, and a digital signal processing device that generates and outputs a cancel signal that cancels the environmental noise based on the converted digital signal A D / A converter that converts the cancel signal into an electric signal, a mixer that mixes and outputs the cancel signal and an externally input music signal, and an electric signal input from the mixer is output as an audible signal A digital noise canceling headphone having a speaker to
The digital signal processor is
Cancel signal generating means for generating the cancel signal;
Level detecting means for detecting the level of the environmental noise;
Level determining means for determining an attenuation level of the cancellation signal according to a detection result of the level means;
A digital noise canceling headphone comprising: a cancel signal level adjusting unit that attenuates and outputs the cancel signal based on the attenuation level.   2. The digital noise canceling phone according to claim 1, wherein the level determining means determines a predetermined coefficient that predefines the attenuation level when the environmental noise is smaller than the reference level.   2. The digital noise canceling phone according to claim 1, wherein the level determining means determines a coefficient relative to the level of the environmental noise when the environmental noise is smaller than the reference level.   2. The digital noise canceling phone according to claim 1, wherein the level determining means determines a coefficient stepwise with respect to the level of the environmental noise when the environmental noise is smaller than the reference level. A microphone that converts environmental noise into an electrical signal, an A / D converter that digitally converts the electrical signal, a digital signal processing device that generates a cancellation signal that cancels the environmental noise based on the converted digital signal, and the cancellation signal A D / A converter that converts the signal into an electric signal, a mixer that mixes and outputs the cancel signal and an externally input music signal, and a speaker that outputs the electric signal input from the mixer as an audible signal, The digital signal processing device generates and outputs the cancellation signal, cancellation signal generation means, level detection means for detecting the environmental noise level, and the cancellation signal attenuation level according to the input level detected by the level means Level determining means for determining the attenuation signal based on the attenuation level Cancel signal level adjusting means so that output, a digital noise cancellation method according to the digital noise canceling headphones having,
The cancel signal generating means generating a cancel signal based on the environmental noise;
The level detecting means detecting the level of the environmental noise;
The level determining means determines the attenuation level of the cancellation signal according to the level of environmental noise detected by the level means;
And a step of attenuating the cancellation signal using the attenuation level determined in the step, and outputting the cancellation signal. The step of determining the attenuation level in the level determining means includes:
6. The digital noise canceling method according to claim 5, wherein when the level detected by the level detecting means is lower than the reference level, the attenuation level is determined as a predetermined coefficient. The step of determining the attenuation level in the level determining means includes:
6. The digital noise canceling method according to claim 5, wherein when the level detected by the level detecting means is smaller than the reference level, a coefficient relative to the level of the environmental noise is determined. The step of determining the attenuation level in the level determining means includes:
6. The digital noise canceling method according to claim 5, wherein when the level detected by the level detecting means is smaller than the reference level, the coefficient is determined stepwise with respect to the environmental noise level.

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