JP6221463B2 - Audio signal processing apparatus and program - Google Patents

Description

  The present invention relates to an audio signal processing apparatus and program, and handles, for example, an audio signal from a telephone or a video conference apparatus (in this specification, an audio signal such as an audio signal or an acoustic signal is called an “audio signal”). It can be applied to communication devices and communication software.

  One of the methods for suppressing the noise component contained in the acquired audio signal is a coherence filter method. As described in Patent Document 1, the coherence filter method is a method of suppressing a noise component having a large bias in the arrival direction by multiplying the cross-correlation of signals having blind spots on the left and right for each frequency.

JP 2013-061421 A

  In addition to coherence filter processing, noise suppression processing may cause distortion in the sound, resulting in unnatural sound quality. One of the causes of distortion is excessive noise suppression processing due to erroneous estimation of noise characteristics. Therefore, in order to prevent excessive suppression, compare the noise suppression coefficient controlled according to the noise situation etc. with a predetermined threshold, and if the noise suppression coefficient is smaller than the threshold, do not use the noise suppression coefficient. In some cases, a flooring process that “a threshold value is a noise suppression coefficient” is used. If the threshold for flooring (hereinafter referred to as the flooring threshold) is too large, the suppression performance is insufficient, and if it is too small, sound distortion increases.

  Therefore, an audio signal processing apparatus and program capable of executing flooring processing that balances noise suppression performance and sound quality are desired.

According to a first aspect of the present invention, (1) a coherence filter coefficient calculating means for calculating a coherence filter coefficient, and (2) the above, in an audio signal processing apparatus that suppresses a noise component contained in an input audio signal by coherence filter processing. Disturbing voice arrival direction index value acquisition means for obtaining an index value representing the arrival direction of the disturbing speech included in the input speech signal; and (3) depending on the acquired index value, the arrival direction of the disturbing speech is the arrival direction of the target speech. Flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as close to, and (4) applying the determined flooring threshold value to the calculated coherence filter coefficient of each frequency. It possesses a flooring processing means for, (5) the interference sound arrival direction index value acquisition means, as the index value, the coherence Fi And calculating the coherence is the arithmetic mean value of the entire frequency of data coefficients.
According to a second aspect of the present invention, (1) a coherence filter coefficient calculating means for calculating a coherence filter coefficient, and (2) the above, in an audio signal processing device that suppresses a noise component contained in an input audio signal by coherence filter processing. Disturbing voice arrival direction index value acquisition means for obtaining an index value representing the arrival direction of the disturbing speech included in the input speech signal; and (3) depending on the acquired index value, the arrival direction of the disturbing speech is the arrival direction of the target speech. Flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as close to, and (4) applying the determined flooring threshold value to the calculated coherence filter coefficient of each frequency. And (5) the disturbing voice arrival direction index value acquisition means has the input voice signal as an index value. And calculates the SN ratio.
According to a third aspect of the present invention, (1) a coherence filter coefficient calculating means for calculating a coherence filter coefficient, and (2) the above, in an audio signal processing device that suppresses a noise component contained in an input audio signal by coherence filter processing. Disturbing voice arrival direction index value acquisition means for obtaining an index value representing the arrival direction of the disturbing speech included in the input speech signal; and (3) depending on the acquired index value, the arrival direction of the disturbing speech is the arrival direction of the target speech. Flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as close to, and (4) applying the determined flooring threshold value to the calculated coherence filter coefficient of each frequency. (5) the flooring threshold value determining means includes a coherence filter coefficient having a high frequency. Flooring threshold is, according to a simple increasing function with a frequency greater than the flooring threshold for low coherence filter coefficients and wherein the determining the flooring threshold.

According to a fourth aspect of the present invention, there is provided an audio signal processing program comprising: a computer mounted in an audio signal processing device that suppresses a noise component included in an input audio signal by coherence filter processing; (1) coherence for calculating coherence filter coefficients; Filter coefficient calculating means, (2) disturbing voice arrival direction index value acquiring means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal, and (3) disturbing according to the acquired index value. A flooring threshold value determining means for determining a flooring threshold value so that the voice arrival direction is closer to the target voice arrival direction, and (4) a coherence filter coefficient calculated for each frequency is determined. by applying the flooring threshold to function as flooring processing means for flooring, (5) the interference sound arrival direction Target value obtaining means, as an index value, and calculates a coherence is the arithmetic mean value of the entire frequency coherence filter coefficients.
The audio signal processing program according to the fifth aspect of the present invention provides a computer mounted on an audio signal processing device that suppresses noise components included in an input audio signal by coherence filter processing. (1) Coherence for calculating coherence filter coefficients Filter coefficient calculating means, (2) disturbing voice arrival direction index value acquiring means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal, and (3) disturbing according to the acquired index value. A flooring threshold value determining means for determining a flooring threshold value so that the voice arrival direction is closer to the target voice arrival direction, and (4) a coherence filter coefficient calculated for each frequency is determined. Function as flooring processing means for performing flooring by applying a flooring threshold, and (5) the disturbing voice arrival direction Standard value acquisition means as an index value, and calculates the SN ratio of the input speech signal.
An audio signal processing program according to a sixth aspect of the present invention includes: (1) a computer mounted in an audio signal processing device that suppresses noise components included in an input audio signal by coherence filter processing; and (2) coherence filter coefficients. Coherence filter coefficient calculating means for calculating; (3) disturbing voice arrival direction index value acquiring means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal; and (4) the acquired index value. In response, flooring threshold value determining means for determining the flooring threshold value so that the arrival direction of the disturbing speech is closer to the arrival direction of the target speech, and (5) for the calculated coherence filter coefficient of each frequency, Functioning as a flooring processing means for performing flooring by applying the determined flooring threshold; Threshold determining means, Flooring threshold for high frequency coherence filter coefficients, in accordance with monotonically increasing function having a frequency greater than the flooring threshold for low coherence filter coefficients, and determines the flooring threshold.

  According to the audio signal processing device and the program of the present invention, the flooring threshold to be applied is switched according to the arrival direction of the disturbing voice, so that it is possible to execute the flooring process that balances the noise suppression performance and the sound quality. it can.

It is a block diagram which shows the whole structure of the audio | voice signal processing apparatus of 1st Embodiment. It is a block diagram which shows the detailed structure of the coherence filter process part in 1st Embodiment. It is explanatory drawing which shows the property of the directivity signal from the directivity formation part in 1st Embodiment. It is explanatory drawing which shows the characteristic of two directivities by the directivity formation part in 1st Embodiment. It is explanatory drawing which shows the behavior of the coherence for every azimuth | direction. It is explanatory drawing which shows a response | compatibility (conversion table) with the coherence which the flooring threshold value determination part in 1st Embodiment incorporates, and a flooring threshold value. It is explanatory drawing which shows an example of the conversion function applied when the flooring threshold value determination part in 1st Embodiment performs the calculation of a conversion function and determines a flooring threshold value. It is a flowchart which shows the flooring process which the flooring process part in 1st Embodiment performs. It is explanatory drawing which shows the directivity of the noise signal produced | generated in 2nd Embodiment.

(A) First Embodiment Hereinafter, a first embodiment of an audio signal processing device and a program according to the present invention will be described in detail with reference to the drawings.

  The audio signal processing apparatus and program according to the first embodiment apply a coherence filter method.

  In general, the value of the coherence filter coefficient greatly fluctuates depending on the arrival direction of noise, particularly human speech other than the speaker (interfering speech). Therefore, when the flooring process is performed, a desired flooring effect cannot be obtained unless the flooring threshold is controlled by the arrival direction.

  The inventor of the present application has recognized that the coherence filter coefficient behaves as follows depending on the arrival direction of the disturbing speech.

  (A) The value increases as the direction of arrival of the disturbing sound approaches the front (the direction of the sound source of the target sound), and the value decreases as it moves sideways. (B) When the direction of arrival of the disturbing voice is close to the front, the high frequency coherence filter coefficient value increases particularly. If these behaviors are organized and described, the suppression performance of the coherence filter decreases as the arrival direction of the interfering speech comes closer to the front, and in particular, the suppression effect of the high frequency interfering speech component decreases.

  In the first embodiment, the flooring threshold is controlled in accordance with the arrival direction of the disturbing voice based on the recognition of the behavior described above.

(A-1) Configuration of First Embodiment FIG. 1 is a block diagram showing a configuration of an audio signal processing device according to the first embodiment. Here, the part excluding the pair of microphones m1 and m2 can be configured by hardware, and can also be realized by software (audio signal processing program) executed by the CPU and the CPU. However, even if any realization method is adopted, it can be functionally represented in FIG.

  In FIG. 1, an audio signal processing apparatus 10 according to the first embodiment includes a pair of microphones m1 and m2, an FFT (Fast Fourier Transform) unit 11, a coherence filter processing unit 12, and an IFFT (Inverse Fast Fourier Transform) unit 13. Have.

  The pair of microphones m1 and m2 are arranged apart from each other by a predetermined distance (or an arbitrary distance), and each captures surrounding sounds. Each of the microphones m1 and m2 is omnidirectional (or has a very gentle directivity in the front direction). Audio signals (input signals) captured by the respective microphones m1 and m2 are converted into digital signals s1 (n) and s2 (n) via corresponding A / D converters (not shown) and given to the FFT unit 11. . Note that n is an index indicating the input order of samples, and is expressed as a positive integer. In the text, it is assumed that the smaller n is the older input sample, and the larger n is the newer input sample.

The FFT unit 11 receives input signal sequences s1 (n) and s2 (n) from the microphones m1 and m2, and performs fast Fourier transform (or discrete Fourier transform) on the input signals s1 and s2. Thereby, the input signals s1 and s2 can be expressed in the frequency domain. In performing the Fast Fourier Transform, analysis frames FRAME1 (K) and FRAME2 (K) composed of predetermined N samples are configured and applied from the input signals s1 (n) and s2 (n). An example of constructing the analysis frame FRAME1 (K) from the input signal s1 (n) is shown in the following equation (1), and the analysis frame FRAME2 (K) is the same.

  K is an index indicating the order of frames and is expressed by a positive integer. In the text, it is assumed that the smaller the K, the older the analysis frame, and the larger, the newer the analysis frame. In the following description, it is assumed that the index representing the latest analysis frame to be analyzed is K unless otherwise specified.

  The FFT unit 11 converts the frequency domain signals X1 (f, K) and X2 (f, K) into the frequency domain signals X1 (f, K) by performing a fast Fourier transform process for each analysis frame. And X2 (f, K) are supplied to the coherence filter processing unit 12, respectively. Note that f is an index representing a frequency. X1 (f, K) is not a single value, but is composed of spectral components of a plurality of frequencies f1 to fm, as shown in equation (2). Furthermore, X1 (f, K) is a complex number and consists of a real part and an imaginary part. The same applies to X2 (f, K) and later-described B1 (f, K) and B2 (f, K).

X1 (f, K) = {X1 (f1, K), X1 (f2, K),..., X1 (fm, K)} (2)
In the coherence filter processing unit 12 to be described later, the frequency domain signal X1 (f, K) of the frequency domain signals X1 (f, K) and X2 (f, K) is mainly used, and the frequency domain signal X2 (f, K) is used. However, the processing may be performed with the frequency domain signal X2 (f, K) as the main and the frequency domain signal X1 (f, K) as the sub (see equation (8) described later).

  The coherence filter processing unit 12 has a detailed configuration shown in FIG. 2 to be described later. The coherence filter processing unit 12 performs coherence filter processing, obtains a signal Y (f, K) in which noise components are suppressed, and supplies the signal Y (f, K) to the IFFT unit 13. is there.

  The IFFT unit 13 performs an inverse fast Fourier transform on the noise-suppressed signal Y (f, K) to obtain an output signal y (n) that is a time domain signal.

  FIG. 2 is a block diagram illustrating a detailed configuration of the coherence filter processing unit 12.

  In FIG. 2, the coherence filter processing unit 12 includes an input signal receiving unit 21, a directivity forming unit 22, a filter coefficient calculation unit 23, an arrival direction estimation unit 24, a flooring threshold value determination unit 25, a flooring processing unit 26, and filter processing. Unit 27 and post-filter processing signal transmission unit 28.

  The input signal receiving unit 21 receives the frequency domain signals X1 (f, K) and X2 (f, K) output from the FFT unit 11.

The directivity forming unit 22 forms two types of directivity signals (first and second directivity signals) B1 (f, K) and B2 (f, K) having strong directivity in a specific direction. . As a method of forming the directivity signals B1 (f, K) and B2 (f, K), an existing method can be applied. For example, a method of obtaining by calculation according to the equations (3) and (4). Can be applied.

  Hereinafter, the meaning of the calculation formulas of the first and second directional signals B1 (f, K) and B2 (f, K) will be described with reference to FIGS. It is assumed that a sound wave arrives from the direction θ shown in FIG. 3A and is captured by a pair of microphones m1 and m2 that are separated by a distance l. At this time, there is a time difference until the sound wave reaches the pair of microphones m1 and m2. This arrival time difference τ is given by equation (5), where d = 1 × sin θ, where d is the sound path difference, and c is the sound speed.

τ = 1 × sin θ / c (5)
Incidentally, a signal s1 (t−τ) obtained by delaying the input signal s1 (n) by τ is the same signal as the input signal s2 (t). Therefore, the signal y (t) = s2 (t) −s1 (t−τ) taking the difference between them is a signal from which the sound coming from the θ direction is removed. As a result, the pair of microphones (microphone array) m1 and m2 have directivity characteristics as shown in FIG.

  In the above, the calculation in the time domain has been described, but the same can be said if it is performed in the frequency domain. The equations in this case are the above-described equations (3) and (4). As an example, it is assumed that the arrival direction θ is ± 90 degrees. That is, the first directivity signal B1 (f) has strong directivity in the right direction as shown in FIG. 4A, and the second directivity signal B2 (f) is shown in FIG. As shown in the figure, it has a strong directivity in the left direction. In the following description, it is assumed that θ = ± 90 degrees. However, θ is not limited to ± 90 degrees.

The filter coefficient calculation unit 23 calculates a coherence filter coefficient coef (f, K) according to the equation (6) based on the first and second directivity signals B1 (f, K) and B2 (f, K). Is.

The arrival azimuth estimation unit 24 obtains an index value that can estimate the noise arrival azimuth and gives it to the flooring threshold value determination unit 25. Here, the arrival direction estimation unit 24 calculates coherence COH (K) as an index value that can estimate the arrival direction of noise. The coherence COH (K) is a value obtained by arithmetically averaging the coherence filter coefficients coef (f, K) at all frequencies as shown in the equation (7).

  FIG. 5 is an explanatory diagram showing the behavior of coherence. As shown in FIG. 5, it can be seen that the range taken by the coherence value changes according to the arrival direction of noise. By using this property, the arrival direction of noise can be estimated.

  The flooring threshold value determination unit 25 determines a flooring threshold value based on the coherence COH (K) calculated by the arrival direction estimation unit 24. The flooring threshold value determination unit 25 determines a flooring threshold value that increases as the noise arrival direction approaches the front (the coherence COH (K) increases), and sets the flooring threshold value for high frequencies. The flooring threshold value is determined so as to be larger than the lower flooring threshold value. If the flooring threshold value determination part 25 can determine such a flooring threshold value, the specific structure will not be ask | required. For example, the flooring threshold value determination unit 25 may determine a flooring threshold value using a conversion table, or may execute a calculation of a conversion function to determine a flooring threshold value.

  FIG. 6 is an explanatory diagram showing the correspondence (conversion table) between the coherence COH (K) and the flooring threshold values for the bands Θ, Ψ, and Φ, which are used in the former determination method.

  As the flooring threshold, different values are set for each of the bands Θ, Ψ, and Φ. For example, if the sampling frequency of the audio signals s1 (n) and s2 (n) is 8000 Hz, the flooring threshold Θ for coherence filter coefficients from 0 to 2000 Hz and the flooring threshold for coherence filter coefficients from 2000 to 3000 Hz. Three thresholds are set as a flooring threshold Φ used for a coherence filter coefficient up to Ψ, 3000 to 4000 Hz. The flooring threshold values Θ, Ψ, and Φ are set to be larger as the arrival direction approaches the front (the coherence COH (K) increases).

  The flooring threshold value determination unit 25 has a given coherence COH (K) in any range A to B, B to C, C to D in the conversion table, (A <B <C <D <. ), And a set of flooring thresholds corresponding to the bands Θ, Ψ, and Φ associated with the range to which it belongs is read and provided to the flooring processing unit 26.

  In the example of FIG. 6, when coherence COH (K) belongs to the range of A ≦ COH (K) <B, Θ = α, Ψ = δ, and Φ = ζ are taken out as a flooring threshold set, When the coherence COH (K) belongs to the range of B ≦ COH (K) <C, Θ = β, Ψ = ε, and Φ = ξ are extracted as a flooring threshold set, and the coherence COH (K) is When belonging to the range of C ≦ COH (K) <D, Θ = γ, Ψ = η, and Φ = ω are taken out as a flooring threshold set. As described above, as the direction of arrival approaches the front, the high frequency coherence filter coefficient increases particularly greatly, and accordingly, the magnitude relationship of the flooring threshold for each band corresponds to the relationship Θ <Ψ <Φ. Specific values α, β, γ, δ, ε, η, ζ, ξ, and ω of the flooring threshold are set so as to satisfy.

  FIG. 7 shows an example of the conversion function used when the flooring threshold value determination unit 25 determines the flooring threshold value by executing the calculation of the conversion function. The conversion function is set for each value of coherence COH (K) (or for each range to which the value belongs).

  In the conversion function, since it is necessary to increase the flooring threshold value as the frequency increases, the slope is set so as to increase as the frequency increases. Further, when a straight line having a different slope for each band is used as the flooring threshold, the slope of the flooring threshold straight line is increased as the noise arrival direction approaches the front. An arbitrary curve may be used as a function for determining the flooring threshold, such as using a curve having a different curvature for each frequency band without being limited to a straight line.

  In the following description of functions and operations of each unit, a case where the conversion table of FIG. 6 is applied will be described.

  The flooring processing unit 26 performs flooring processing by applying the flooring threshold determined by the flooring threshold determination unit 25 to the coherence filter coefficient coef (f, K). For example, when the frequency fi belongs to the lowest band Θ, for the flooring process of the coherence filter coefficient coef (fi, K), the flooring processing unit 26 determines the flooring thresholds α, β or Apply γ (see FIG. 6). For example, when the frequency fi belongs to the second band Ψ from the lowest, the flooring processing unit 26 performs the flooring determined for the band Ψ for the flooring process of the coherence filter coefficient coef (fi, K). The threshold δ, ε or η (see FIG. 6) is applied. Further, for example, when the frequency fi belongs to the highest band Φ, for the flooring process of the coherence filter coefficient coef (fi, K), the flooring processing unit 26 determines the flooring thresholds ζ and ξ determined for the band Φ. Alternatively, ω (see FIG. 6) is applied.

  The filter processing unit 27 applies the coherence filter coefficient flcoef (f, K) after the flooring process, and performs the coherence filter process on the main frequency domain signal X1 (f, K) as shown in the equation (8). To obtain a noise-suppressed signal (filtered signal) Y (f, K). In addition, (8) Formula represents each calculation (multiplication process) of each frequency.

Y (f, K) = X1 (f, K) × flcoef (f, K) (8)
Here, the physical meaning of the coherence filter process will be supplemented. The coherence filter coefficient coef (f, K) (the same applies to the post-flooring coherence filter coefficient flcoef (f, K)) is a cross-correlation of signal components having blind spots on the left and right. Is a voice component arriving from the front with no bias, and when the correlation is small, the arrival azimuth is a component biased to the right or left. Therefore, multiplication by the coherence filter coefficient coef (f, K) can be said to be processing for suppressing a noise component coming from the side.

  The post-filter processing signal transmission unit 28 supplies the post-noise suppression signal Y (f, K) to the IFFT unit 13 at the subsequent stage. Further, the post-filter processing signal transmission unit 28 increases K by 1 and starts processing of the next frame.

(A-2) Operation of the First Embodiment Next, the operation of the audio signal processing device 10 of the first embodiment will be described in the order of overall operation and detailed operation in the coherence filter processing unit 12 with reference to the drawings. To do.

  Signals s1 (n) and s2 (n) input from the pair of microphones m1 and m2 are respectively converted from time domain to frequency domain signals X1 (f, K) and X2 (f, K) by the FFT unit 11. Is then provided to the coherence filter processing unit 12. Thus, the coherence filter processing unit 12 performs coherence filter processing, and the obtained noise-suppressed signal Y (f, K) is provided to the IFFT unit 13. In IFFT section 13, noise-suppressed signal Y (f, K), which is a frequency domain signal, is converted into time domain signal y (n) by inverse fast Fourier transform, and this time domain signal y (n) is output. Is done.

  Next, a detailed operation in the coherence filter processing unit 12 will be described. In the following, processing of a certain frame will be described, but such frame-based processing is repeated for each frame.

  When the frequency domain signals X1 (f, K) and X2 (f, K) of the new frame (current frame K) are given from the FFT unit 11, the directivity forming unit 22 (3) The first and second directional signals B1 (f, K) and B2 (f, K) are calculated according to the equations (4) and (4), and these directional signals B1 (f, K) and B2 ( Based on (f, K), the filter coefficient calculation unit 23 calculates the coherence filter coefficient coef (f, K) according to the equation (6).

  Based on the calculated coherence filter coefficient coef (f, K), the coherence COH (K) is calculated by the arrival azimuth estimation unit 24 as an index value that can estimate the noise arrival azimuth according to the equation (7). . The flooring threshold value determination unit 25 determines which range A to B, B to C, C to D,... Of the conversion table the calculated coherence COH (K) belongs to. A set of flooring threshold values for each band Θ, Ψ, and Φ attached is read from the conversion table. Accordingly, the flooring processing unit 26 applies the read flooring threshold to the coherence filter coefficient coef (f, K) and executes the flooring process.

  FIG. 8 is a flowchart showing the flooring process executed by the flooring processing unit 26.

  The flooring processing unit 26 uses a flooring threshold TH (K) (= α, β) in which a coherence filter coefficient coef (fi, K) of a certain frequency fi is read for the band Θ, Ψ, or Φ to which the frequency fi belongs. , Γ, δ, ε, η, ζ, ξ, or ω) (step S1). If the coherence filter coefficient coef (fi, K) is smaller than the flooring threshold TH (K) The flooring threshold TH (K) is set to the coherence filter coefficient flcoef (fi, K) after the flooring process (step S2), and the coherence filter coefficient coef (fi, K) is equal to or greater than the flooring threshold TH (K). In this case, the coherence filter coefficient coef (fi, K) is directly used as the coherence filter coefficient flcoef (f Is set to K) (step S3).

  By applying the coherence filter coefficient flcoef (f, K) after the flooring process, the filter processing unit 27 performs the coherence filter process for the main frequency domain signal X1 (f, K) as shown in the equation (8). The obtained noise-suppressed signal (filtered signal) Y (f, K) that is executed is provided to the IFFT unit 13 by the filtered signal transmitter 28, and the frame variable K is increased by 1, Processing proceeds to the next frame.

(A-3) Effects of the First Embodiment According to the first embodiment, the flooring threshold determined according to the arrival direction of the disturbing speech is applied, and the flooring process is performed on the coherence filter coefficient. Therefore, a flooring process that balances noise suppression performance and sound quality can be executed, and a desired effect by the flooring process can be obtained.

  Here, since the high-frequency flooring threshold is set based on the unique behavior that the high-frequency coherence filter coefficient increases as the arrival direction approaches the front, the above effect can be further exhibited.

  As a result, it is possible to expect improvement in call sound quality in a communication device such as a video conference device or a mobile phone to which the audio signal processing device or program of the first embodiment is applied.

(B) Second Embodiment Next, a second embodiment of the audio signal processing apparatus and program according to the present invention will be described.

  In the first embodiment, coherence COH is applied as an index value representing the arrival direction of disturbing speech. In the second embodiment, the SN ratio SNR (K) is applied instead of the coherence COH (K) as an index value representing the arrival direction of the disturbing speech.

  The overall configuration of the audio signal processing apparatus according to the second embodiment can be represented by FIG. 1 used in the description of the first embodiment. The detailed configuration of the coherence filter processing unit of the second embodiment can also be represented by FIG. 2 used in the description of the first embodiment.

  However, as described above, the arrival direction estimation unit 24 calculates the SN ratio SNR (K) instead of the coherence COH (K), unlike the first embodiment. The flooring threshold value determination unit 25 determines a flooring threshold value for each band based on the calculated SN ratio SNR (K).

  Hereinafter, a method for calculating the SN ratio SNR (K) executed by the arrival direction estimation unit 24 of the second embodiment will be described.

  The arrival direction estimation unit 24 calculates the noise signal N (f, K) according to the equation (9) based on the frequency domain signals X1 (f, K) and X2 (f, K). The calculation of equation (9) corresponds to a process of forming directivity having a blind spot on the front as shown in FIG. Therefore, only components coming from the left and right can be obtained. Since the target direction is assumed to be the front direction (for example, the target speaker is assumed to be in front), it can be said that the component coming from the side is noise.

N (f, K) = X1 (f, K) -X2 (f, K) (9)
Next, the arrival direction estimation unit 24, based on the main frequency domain signal X1 (f, K) and the noise signal N (f, K), according to the equation (10), the SN ratio SNR (K in the current frame K) ). The denominator of equation (10) is the level of the noise signal, and the numerator is the level of the target sound signal. Since it is assumed that the target sound comes from the front and the noise comes from the side (left and right), the S / N ratio can be estimated by equation (10). In the equation (10), η is a parameter larger than 0 and smaller than 1.

  The SN ratio SNR (K) calculated as described above is applied as an index value representing the arrival direction of disturbing speech, and flooring corresponding to the arrival direction of disturbing speech is performed in the same manner as in the first embodiment described above. Determine the threshold.

  Also in the second embodiment, the flooring threshold determined in accordance with the arrival direction of the disturbing speech is applied and the flooring process is performed on the coherence filter coefficient. Therefore, the same effect as that of the first embodiment can be obtained. Can play.

(C) Other Embodiments In the description of each of the above embodiments, various modified embodiments have been referred to, but further modified embodiments as exemplified below can be given.

  In the first embodiment, coherence COH (K) is applied as an index value representing the arrival direction of disturbing speech, and in the second embodiment, the SN ratio SNR (K) is an index value representing the arrival direction of disturbing speech. However, as long as it represents the arrival direction of disturbing speech, other index values may be applied, or a plurality of index values may be applied simultaneously. For example, the flooring threshold TH (K) may be determined according to the combination of the range to which the coherence COH (K) belongs and the range to which the SN ratio SNR (K) belongs.

  In each of the above embodiments, the number of bands for switching the flooring threshold (or the flooring threshold calculation function) is three, but the number of bands may be two or more.

  In each of the above embodiments, the processing that was processed with the frequency domain signal may be performed with the time domain signal if possible, and conversely, the processing that was processed with the time domain signal is possible. In this case, processing may be performed using a frequency domain signal.

  In each of the above-described embodiments, the noise suppression technique is shown by applying the coherence filter method alone, but other noise suppression techniques (see Patent Document 1), for example, the voice switch method, the Wiener filter method, the frequency subtraction method, and the like. You may make it use together.

  In each of the above-described embodiments, the audio signal processing apparatus and the program that immediately process the signal captured by the pair of microphones are shown, but the audio signal to be processed of the present invention is not limited to this. For example, the present invention can be applied to processing a pair of audio signals read from a recording medium, and the present invention can also be applied to processing a pair of audio signals transmitted from the opposite device. Can be applied.

  DESCRIPTION OF SYMBOLS 10 ... Audio | voice signal processing apparatus, 11 ... FFT part, 12 ... Coherence filter processing part, 13 ... IFFT part, m1, m2 ... Microphone, 21 ... Input signal receiving part, 22 ... Directivity formation part, 23 ... Filter coefficient calculation part , 24 ... arrival direction estimation unit, 25 ... flooring threshold value determination unit, 26 ... flooring processing unit, 27 ... filter processing unit, 28 ... post-filter processing signal transmission unit.

Claims (9)

In an audio signal processing apparatus that suppresses noise components included in an input audio signal by coherence filter processing,
Coherence filter coefficient calculating means for calculating a coherence filter coefficient;
Disturbing voice arrival direction index value obtaining means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal;
In accordance with the acquired index value, a flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as the arrival direction of the disturbing speech is closer to the arrival direction of the target speech;
To the calculated coherence filter coefficient of each frequency, by applying the determined Flooring threshold possess a flooring processing means for flooring,
The disturbing sound arrival direction index value acquisition means, as the index value, the audio signal processing apparatus characterized by calculating the coherence is the arithmetic mean value of the entire frequency coherence filter coefficients. In an audio signal processing apparatus that suppresses noise components included in an input audio signal by coherence filter processing,
Coherence filter coefficient calculating means for calculating a coherence filter coefficient;
Disturbing voice arrival direction index value obtaining means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal;
In accordance with the acquired index value, a flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as the arrival direction of the disturbing speech is closer to the arrival direction of the target speech;
Flooring processing means for performing flooring by applying the determined flooring threshold to the calculated coherence filter coefficient of each frequency;
The disturbing sound arrival direction index value acquisition means, as the index value, features and be Ruoto voice signal processor to calculate the SN ratio of the input speech signal. In an audio signal processing apparatus that suppresses noise components included in an input audio signal by coherence filter processing,
Coherence filter coefficient calculating means for calculating a coherence filter coefficient;
Disturbing voice arrival direction index value obtaining means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal;
In accordance with the acquired index value, a flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as the arrival direction of the disturbing speech is closer to the arrival direction of the target speech;
Flooring processing means for performing flooring by applying the determined flooring threshold to the calculated coherence filter coefficient of each frequency;
The flooring threshold value determining means determines the flooring threshold value according to a simple increasing function in which the flooring threshold value for the coherence filter coefficient having a high frequency is larger than the flooring threshold value for the coherence filter coefficient having a low frequency. Ruoto voice signal processing apparatus. 4. The audio signal processing apparatus according to claim 3 , wherein the simple increase function is a step function. 4. The audio signal processing apparatus according to claim 3 , wherein the simple increase function is a polygonal function having a larger slope on the higher frequency side. 4. The audio signal processing apparatus according to claim 3 , wherein the simple increase function is a function obtained by connecting a plurality of curved functions. A computer mounted on an audio signal processing device that suppresses noise components contained in the input audio signal by coherence filter processing,
Coherence filter coefficient calculating means for calculating a coherence filter coefficient;
Disturbing voice arrival direction index value obtaining means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal;
In accordance with the acquired index value, a flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as the arrival direction of the disturbing speech is closer to the arrival direction of the target speech;
Apply the determined flooring threshold to the calculated coherence filter coefficient of each frequency to function as a flooring processing means for performing flooring ,
The speech signal processing program characterized in that the disturbing speech arrival direction index value acquisition means calculates coherence, which is an arithmetic average value at all frequencies of the coherence filter coefficient, as the index value . A computer mounted on an audio signal processing device that suppresses noise components contained in the input audio signal by coherence filter processing,
Coherence filter coefficient calculating means for calculating a coherence filter coefficient;
Disturbing voice arrival direction index value obtaining means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal;
In accordance with the acquired index value, a flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as the arrival direction of the disturbing speech is closer to the arrival direction of the target speech;
Flooring processing means for performing flooring by applying a determined flooring threshold to the calculated coherence filter coefficient of each frequency;
To function,
The disturbing voice arrival direction index value acquisition means calculates an SN ratio of the input voice signal as an index value.
An audio signal processing program. A computer mounted on an audio signal processing device that suppresses noise components contained in the input audio signal by coherence filter processing,
Coherence filter coefficient calculating means for calculating a coherence filter coefficient;
Disturbing voice arrival direction index value obtaining means for obtaining an index value representing the arrival direction of disturbing voice included in the input voice signal;
In accordance with the acquired index value, a flooring threshold value determining means for determining a flooring threshold value so as to take a larger value as the arrival direction of the disturbing speech is closer to the arrival direction of the target speech;
Flooring processing means for performing flooring by applying a determined flooring threshold to the calculated coherence filter coefficient of each frequency;
To function,
The flooring threshold value determining means determines a flooring threshold value according to a simple increasing function in which a flooring threshold value for a coherence filter coefficient having a high frequency is larger than a flooring threshold value for a coherence filter coefficient having a low frequency.
An audio signal processing program.

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