JP5424396B2 - Amplifying device having Doppler distortion compensation function - Google Patents

Description

  The present invention relates to a Doppler distortion compensator that compensates in advance for Doppler distortion generated in a speaker that emits sound at an amplifier stage.

  In a loudspeaker that combines an amplifier and a speaker, distortion generated in the amplifier can be relatively easily reduced. However, in principle, a distortion called Doppler distortion is generated in the speaker, which causes distortion in the sound emitted by the speaker. The Doppler distortion is often smaller than the distortion due to other non-linear factors of the speaker, but the influence on the sound feeling is often not negligible.

  The Doppler distortion is a distortion generated when the frequency of the sound generated by the Doppler effect caused by the vibration of the diaphragm of the speaker deviates from the frequency of the original signal. That is, distortion generated by a frequency shift proportional to the moving speed of the diaphragm of the speaker.

  As an effective means for reducing the Doppler distortion, there is a multi-way speaker. Doppler distortion becomes prominent when low frequency components and high frequency components coexist. Therefore, by changing the speaker that generates sound for each frequency band, it is not necessary to generate a low-frequency signal and a high-frequency signal with a single speaker, and as a result, Doppler distortion can be kept small. However, even if the multi-way method is performed, the frequency division is not usually performed as much as 2 ways or 3 ways, and it is difficult to sufficiently reduce the Doppler distortion.

  Patent Document 1 proposes a method for compensating in advance for non-linear distortion of a speaker at the stage of an amplifier. However, this method has a problem that when the PCM signal is compensated by digital processing and the sound source signal contains a high frequency component close to the Nyquist frequency, the compensation accuracy in the high frequency range is not good. It was. In addition, when trying to perform Doppler distortion compensation for a multi-way speaker, there is a problem that the compensation accuracy near the crossover frequency is not good.

Japanese Patent Application No. 2009-182570

  The problem to be solved is to reduce the Doppler distortion generated by a system in which the speaker and the amplifier are combined by accurately compensating for the Doppler distortion generated in the speaker in advance at the stage of the audio signal.

  In order to solve the above problems, a sound pressure estimation filter that estimates the sound pressure generated by the speaker including Doppler distortion is prepared, and compensation is made so that the sound pressure estimated by the sound pressure estimation filter is proportional to the audio input signal. By generating a filter output signal and making the speaker drive signal proportional to the compensation filter output signal, the sound pressure generated by the speaker is made proportional to the audio input signal and the Doppler distortion caused by the speaker is compensated.

  First, consider the case of driving a single speaker. The same applies to the case of driving a plurality of equivalent speakers.

  Doppler distortion can be interpreted as a result of the frequency of the sound observed by the observer shifting with respect to the frequency of the signal driving the speaker depending on the speed of the speaker's cone displacement. It can also be interpreted as distortion generated by the change in the phase of the sound observed by a person. These two interpretations are due to differences in thinking and are equivalent.

Consider the system shown in FIG. Now, let the displacement of the cone of the speaker 3 be p (t). Where t is the time. Further, an input signal to the compensator 1 u (t), s the output signal of the compensator 1 v from (t), the sound pressure observer observes s _o (t), v for the small signal (t) _o G (s) is the transmission to (t). In addition, the sound pressure observed by the observer when Doppler distortion is not included is s (t). That is,
(Equation 1)
S (s) = G (s) V (s)
And However, V (s) is a Laplace transform of v (t), and S (s) is a Laplace transform of s (t). As for the displacement of the cone of the speaker 3 as p (t), the transfer function H (s) from v (t) to p (t) is experimentally measured in advance. Then, p (t) can be estimated from v (t). At this time, the sound pressure observed by the observer for non-small v (t) is (Equation 2)
s _o (t) = s (tp (t) / c)
It becomes. Where c is the speed of sound.

Here, using the variable dead time element (Equation 3)
v (t) = u (t + τ-p (t) / c)
Consider the case. However, τ is a fixed dead time,
(Equation 4)
τ-p (t) / c> 0
Shall be satisfied. Even if the signal can be delayed in the time direction, it cannot be advanced, so a certain dead time τ is provided. Then, the fluctuation of the dead time causing Doppler distortion is offset, and the sound pressure observed by the observer is (Equation 5).
S _o (s) = G (s) U (s) exp (-τs)
It becomes. However, S _o (s) is the Laplace transform of s _o (t).

  The variable dead time element (Equation 3) can be realized by an FIR filter or the like having a variable parameter, and such a variable dead time element is used in a sample rate converter or the like.

  Furthermore, as a variable dead time element, not only is the dead time changed purely as shown in (Equation 3), but the frequency response gain has a reverse characteristic of G (s), so that the frequency characteristic of a speaker, etc. You may make it compensate.

  In this case, the variable dead time element can be designed as follows. First, G (s) is converted into a state variable expression.

Then, the time is changed to discrete time including the fluctuating dead time τ-p (t).

However, T is a sampling period, and p [k] is a signal obtained by converting p (t) into discrete time according to the sampling period. Further, v [k] is an output signal of the compensator that has been made discrete time. Then, y [k] becomes a signal advanced by s ₀ (t) for a certain time. Then, v [k] is calculated as follows.

Then, y [k] because the one-sample delayed signal to the _{u [k], s o (} t) is a signal which is delayed for a given length of time u [k]. That is, the sound pressure observed by the observer may not include Doppler distortion that is faithful to the audio input signal u [k].

  Next, consider a case where two types of speakers having different characteristics are driven by a single amplifier 2 (FIG. 1). Here, it is assumed that two types of speakers are a woofer 3a and a tweeter 3b.

Now, let the displacement of the woofer 3a be p _w (t) and the displacement of the cone of the tweeter 3b be p _t (t). Further, the woofer an input signal to the compensator 1 from u (t), the output signal of the compensator 1 v (t), the sound pressure observer observes s _o (t), v for the small signal (t) s _o a transfer to the _{(t) G w (s)} , the transfer of s _o to (t) through the tweeter from the v (t) and G _t (s) through. In addition, the sound pressure through the woofer observed by the observer when Doppler distortion is not included is s _w (t), and the sound pressure through the tweeter is s _t (t). That is,

And However, V (s) is a Laplace transform of v (t), and S _w (s) is a Laplace transform of s _w (t). Furthermore, the transfer function H _w (s) from v (t) to p _w (t) and the transfer function H _t (s) from v (t) to p _t (t) are experimentally measured in advance. Shall. Then, p _w (t) and p _t (t) can be estimated from v (t). At this time, the sound pressure observed by the observer for v (t) that is not very small is

It becomes. The observer calculates the v [k] such that the predetermined time delayed signal to the sound pressure _{s o (t) u [k} ] an audio input signal to be observed.

First, G _w (s) and G _t (s) are converted into state variable expressions.

Then, the time is changed to discrete time including the fluctuating dead time τ-p (t).

However, T is the sampling period, p _w [k] is a signal obtained by discrete-time in accordance with the sampling period of _{p w (t), p t} [k] is the discrete time in accordance with the sampling period of p _t (t) Signal. Further, v [k] is an output signal of the compensator that has been made discrete time. Then, y [k] in the following equation becomes a signal advanced by s ₀ (t) for a certain time.

Then, v [k] is calculated as follows.

Then, s _o (t) is a signal which is delayed for a given length of time u [k]. That is, the sound pressure observed by the observer may not include Doppler distortion that is faithful to the voice input signal. However, the compensator constituted by Equations 13, 14, and 16 needs to be stable. That is, the signal v [k] needs not to diverge with time. Although it is difficult to specify exactly the conditions for the compensator to be stable, using this approach places constraints on G _w (s) and G _t (s).
Here, although two types of speakers, the woofer 3a and the tweeter 3b, are used, the number of types of speakers can be further increased by the same method.

  The amplification device having the Doppler distortion compensation function of the present invention has an advantage that the Doppler distortion can be accurately compensated for a plurality of types of speakers (multi-way speakers).

The block diagram which shows the structure of the amplifier and speaker which include the Doppler distortion compensator in the 4th Embodiment of this invention. 1 is a block diagram showing a configuration of an amplifier and a speaker including a Doppler distortion compensator according to a first embodiment of the present invention. The block diagram which shows another structure of the amplifier and speaker which include the Doppler distortion compensator in the 1st Embodiment of this invention. The block diagram which shows the structure of the amplifier and speaker which include the Doppler distortion compensator in the 2nd Embodiment of this invention. The block diagram which shows another structure of the amplifier and speaker which include the Doppler distortion compensator in the 2nd Embodiment of this invention. The block diagram which shows the structure of the amplifier and speaker which include the Doppler distortion compensator in the 3rd Embodiment of this invention. The block diagram which shows another structure of the amplifier and speaker which include the Doppler distortion compensator in the 4th Embodiment of this invention. The block diagram which shows the structure of the amplifier and speaker which include the Doppler distortion compensator in the 5th Embodiment of this invention. The block diagram which shows the structure of the amplifier and speaker which include the Doppler distortion compensator in the 6th Embodiment of this invention.

  A first embodiment of the present invention is shown in FIG. The audio input signal u (t) is a signal subjected to volume processing. A transfer function from the signal v (t) to the cone displacement of the speaker 3 is obtained in advance by an experimental method or the like, and the transfer function is defined as H (s). Then, the cone displacement of the speaker 3 can be estimated by applying the transfer function H (s) to the signal v (t). Let the estimated cone displacement of the speaker 3 be p (t). The compensator 12 is composed of the following FIR filter.

Here, the function f (t) is a time function designed in advance, and a sinc function or the like can be used. N is an integer parameter that determines the order of the filter, and T is the sampling period. The signal u [k] is a signal obtained by sampling the audio input signal u (t), and the signal v (t) is a signal obtained by passing a zero-order hold with respect to the signal v [k]. By appropriately designing the function f (t), the compensator 12 operates as a dead time element within a specific frequency range. Since the dead time in the compensator 12 is changed in accordance with the amount of change in the delay time caused by the cone displacement of the speaker 3, a sound pressure signal in which the Doppler distortion is compensated can be generated from the speaker 3. .

  In the first embodiment of the present invention, the cone displacement of the speaker 3 is estimated on the basis of the signal v (t). However, since the compensation amount in the compensator 12 is small, as shown in FIG. The cone displacement of the speaker 3 may be estimated based on the input signal u (t).

  A second embodiment of the present invention is shown in FIG. The audio input signal u [k] is a discrete time signal having a sampling period T, and is a volume-processed signal. A transfer function from the signal v [k] to the cone displacement of the speaker 3 is obtained in advance by an experimental method or the like, and the transfer function is H [z]. Then, the cone displacement of the speaker 3 can be estimated by applying the transfer function H [z] to the signal v [k]. Let the estimated cone displacement of the speaker 3 be p [k]. Further, a transfer function G (s) for a minute signal from the signal v [k] to the sound pressure is also experimentally obtained in advance. The compensator 12 calculates a signal v [k], which is an output signal, according to Equation 8. Further, the state variable vector x [k] in Equation 8 is updated every sample according to Equation 7. At this time, the dead time in the compensator 12 is changed in accordance with the amount of change in the delay time caused by the cone displacement of the speaker 3, and as a result, a sound pressure signal in which the Doppler distortion is compensated is generated from the speaker 3. be able to. Since the compensator 12 also compensates for the frequency characteristics of the amplifier 2 and the speaker 3, the sound pressure signal generated from the speaker 3 is not only the Doppler distortion in the speaker 3 but also the frequency characteristics of the amplifier 2 and the speaker 3. It becomes a compensated sound pressure signal.

  In the second embodiment of the present invention, the cone displacement of the speaker 3 is estimated based on the signal v [k]. However, since the compensation amount in the compensator 12 is small, as shown in FIG. The cone displacement of the speaker 3 may be estimated based on the input signal u [k]. At this time, it is assumed that the transfer function G (s) for the minute signal from the signal v [k] to the sound pressure is normalized so as to be approximately 1 in the main sound range.

  A third embodiment of the present invention is shown in FIG. In this method, two types of speakers 3a and 3b are driven using two amplifiers 2a and 2b, and compensators 1a and 1b are prepared for the respective speakers 3a and 3b.

The combination of the compensator 1a, the amplifier 2a, and the speaker 3a and the combination of the compensator 1b, the amplifier 2b, and the speaker 3b are the same as those in the second embodiment of the present invention. The cone displacement estimator 11c calculates an estimated value p _w [k] of the cone position of the speaker 3a, and the compensation element 12a is designed from the combined characteristics of the amplifier 2a and the speaker 3a. Further, the cone displacement estimator 11d calculates an estimated value p _t [k] of the cone position of the speaker 3b, and the compensation element 12b is designed from the combined characteristics of the amplifier 2b and the speaker 3b.

  In the third embodiment of the present invention, since Doppler distortion compensation is performed independently for the two types of speakers 3a and 3b, there is an advantage that there is no restriction on the combination of the two types of speakers 3a and 3b. ing.

In the third embodiment of the present invention, the speaker 3a and the speaker 3b are estimated using the signal v _w [k] and the signal v _t [k], but the compensators 1a and 1b in FIG. 5, the cone position estimates p _w [k] and p _t [k] are approximately calculated based on the audio input signal u [k]. Also good.

A fourth embodiment of the present invention is shown in FIG. In FIG. 1, a frequency discrimination filter called a network is not specified, but when a network is installed between the amplifier 2 and the speakers 3a and 3b, they are included in the speakers 3a and 3b. Shall be interpreted. The audio input signal u [k] is a discrete time signal having a sampling period T, and is a volume-processed signal. A transfer function from the signal v [k] to the cone displacement of the speakers 3a and 3b is obtained in advance by an experimental method or the like, and the transfer functions are H _w [z] and H _t [z]. Then, the cone displacement of the speaker 3a and the speaker 3b can be estimated by applying the transfer function H [z] to the signal v [k]. The estimated cone displacements of the speaker 3 are defined as p _w [k] and p _t [k]. Further, a transfer function G _w (s) for a minute signal from the signal v [k] to the sound pressure through the speaker 3a and a transfer function G _t for a minute signal from the signal v [k] to the sound pressure through the speaker 3b. (s) is also experimentally obtained in advance. The compensator 12 calculates a signal v [k], which is an output signal, according to Equation 16. Further, the state variable vectors x _w [k] and x _t [k] in Expression 16 are updated every sample according to Expression 13 and Expression 14. As a result, the sound pressure signals generated from the speakers 3a and 3b become sound pressure signals in which not only the Doppler distortion in the speakers 3a and 3b but also the frequency characteristics of the amplifier 2 and the speakers 3a and 3b are compensated.

  In the fourth embodiment of the present invention, the two-way speaker constituted by the speakers 3 a and 3 b is driven by the single amplifier 2, but a speaker having multiple ways may be driven by the single amplifier 2. In this case, the signal v [k] is calculated so that the total sound pressure generated by all the speakers follows the audio input signal u [k].

In the fourth embodiment of the present invention, the cone displacement of the speakers 3a and 3b is estimated based on the signal v [k]. However, since the compensation amount in the compensator 12 is small, as shown in FIG. Alternatively, the cone displacement of the speaker 3 may be estimated based on the audio input signal u [k]. At this time, it is assumed that the transfer function G _w (s) + G _t (s) for the minute signal from the signal v [k] to the sound pressure is normalized so as to be approximately 1 in the main sound range.

  A fifth embodiment of the present invention is shown in FIG. This is a system in which a three-way speaker composed of three kinds of speakers 3a, 3b and 3c is driven by two amplifiers 2a and 2b. Although the filter called the network is not explicitly shown in FIG. 8, when the network is installed, they are assumed to be included in the speakers 3a, 3b and 3c.

  The speakers 3a and 3b are driven by the method shown in the fourth embodiment of the present invention. Therefore, the Doppler distortion generated by the speakers 3a and 3b is compensated by the compensator 1a. Further, the speaker 3c is driven by the method shown in the second embodiment of the present invention. Therefore, the Doppler distortion generated by the speaker 3c is compensated by the compensator 1b. As a result, all the Doppler distortion generated by the speakers 3a, 3b and 3c is compensated.

  FIG. 9 shows a sixth embodiment of the present invention. This is a system in which a three-way speaker composed of three kinds of speakers 3a, 3b and 3c is driven by two amplifiers 2a and 2b. Although the filter called the network is not explicitly shown in FIG. 8, when the network is installed, they are assumed to be included in the speakers 3a, 3b and 3c.

  The speakers 3a and 3b are driven by the method shown in the fourth embodiment of the present invention. Therefore, the Doppler distortion generated by the speakers 3a and 3b is compensated by the compensator 1a. The speaker 3c is driven by compensating for Doppler distortion by a method other than the method shown in the second embodiment of the present invention. For example, the Doppler distortion is compensated in the compensator 4 by the method described in Japanese Patent Application No. 2009-182570, and the speaker 3c is driven. Therefore, the Doppler distortion generated by the speaker 3 c is compensated by the compensator 4. As a result, all the Doppler distortion generated by the speakers 3a, 3b and 3c is compensated.

  The method shown in the fourth embodiment of the present invention has an advantage that the Doppler distortion generated by a plurality of speakers can be accurately compensated, but the speaker cone displacement can be compensated from the sampling period T of the signal processing. The amplitude is limited. In the case of the sixth embodiment of the present invention, if the speaker 3a is a squawker and the speaker 3b is a tweeter, both the squawker and the tweeter have a small cone displacement amplitude. The method described in the embodiment can be used without any problem. On the other hand, if the speaker 3c is a woofer, the amplitude of the cone displacement of the woofer is often large, so there is a problem that the sampling period T of the signal processing cannot be made very short. On the other hand, the method described in Japanese Patent Application No. 2009-182570 has a problem that the accuracy of Doppler distortion compensation near the crossover frequency is poor when there are a plurality of types of speakers. There is no. Moreover, since the Doppler distortion to be compensated by the compensator 4 is a single type of speaker, the problem of compensation accuracy near the crossover frequency that the method described in Japanese Patent Application No. 2009-182570 does not occur.

  By using the Doppler distortion compensator of the present invention, it is possible to realize a loudspeaker that generates a sound that cancels out the Doppler distortion generated in a speaker.

DESCRIPTION OF SYMBOLS 1, 1a, 1b ... Distortion compensation apparatus 11, 11a, 11b, 11c, 11d ... Cone displacement estimator 12, 12a, 12b, 12c ... Compensator 2, 2a, 2b ... Amplifier 3, 3a, 3b, 3c ... speaker 4 ... distortion compensation device

Claims (4)

A sound input signal is input, a speaker drive signal for driving one kind of speaker is output, a distortion compensation device that compensates for Doppler distortion generated by the speaker, and an output signal of the distortion compensation device is input, and the speaker drive signal is input. The distortion compensator has a cone displacement estimator that inputs the voice input signal and outputs a cone displacement estimation value of the speaker, and the voice input signal that is input to the distortion compensation apparatus. A distortion compensator for output, and the distortion compensator has an output vector calculated based on the cone displacement estimation value and a variable dead time element expressed by a discrete-time state variable having a direct arrival coefficient, and outputs the distortion compensator The signal is divided by the direct factor for the value obtained by subtracting the product of the output vector and the state variable vector of the variable dead time element from the voice input signal. Amplifier having a Doppler distortion compensating function, characterized by a value. Distortion compensator for inputting audio input signal, outputting a single speaker driving signal for driving plural kinds of speakers, and compensating for comprehensive Doppler distortion generated by the plural kinds of speakers, and output of the distortion compensator The distortion compensator receives the sound input signal and outputs a cone displacement estimation value of each of the plurality of types of speakers, and the sound It has a distortion compensator that inputs an input signal and outputs an output signal of the distortion compensator, and the distortion compensator has a respective output vector calculated based on each of the cone displacement estimation values and a direct reach coefficient. Each variable dead time element is represented by a discrete-time state variable expression, and the output signal of the distortion compensator is output from the audio input signal. Doppler distortion compensating function, characterized in that the vector and divided by the sum of each of the feedthrough factor to each value obtained by subtracting the sum of the product of the state variable vector of each of the variable dead time element Amplifying device having. A sound input signal is input, a speaker drive signal for driving one kind of speaker is output, a distortion compensation device that compensates for Doppler distortion generated by the speaker, and an output signal of the distortion compensation device is input, and the speaker drive signal is input. An output amplifier, the distortion compensator inputs a signal from the distortion compensator and outputs a cone displacement estimation value of the speaker; and inputs the voice input signal to the distortion compensator. A distortion compensator for outputting an output signal, and the distortion compensator has a variable dead time element represented by a discrete time state variable expression having an output vector calculated based on the cone displacement estimation value and a direct arrival coefficient, and the distortion compensation The output signal of the measuring device is obtained by subtracting the product of the output vector and the state variable vector of the variable dead time element from the voice input signal. Amplifier having a Doppler distortion compensating function, characterized in that a value obtained by dividing. Distortion compensator for inputting audio input signal, outputting a single speaker driving signal for driving plural kinds of speakers, and compensating for comprehensive Doppler distortion generated by the plural kinds of speakers, and output of the distortion compensator A cone displacement estimator which has an amplifier which receives a signal as an input and outputs the speaker drive signal, and wherein the distortion compensator receives an output signal of the distortion compensator and outputs an estimated cone displacement value of each of the plurality of types of speakers; And a distortion compensator that inputs the audio input signal and outputs an output signal of the distortion compensator, and the distortion compensator calculates each output vector calculated based on each estimated cone displacement value and each direct reach Each variable dead time element is represented by a discrete time state variable expression having a coefficient, and the output signal of the distortion compensator is derived from the voice input signal. A value obtained by subtracting the sum of the products of the output vectors and the state variable vectors of the variable dead time elements and dividing the sum by the sum of the direct delivery coefficients. An amplifying device having a distortion compensation function.