JP2008005094A - Echo suppressing method and device, echo suppressing program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an echo suppressing method and a device with less deterioration of sound quality even during double talk. <P>SOLUTION: A microphone reception signal performs frequency domain transformation, gains for suppressing echoes are obtained for each frequency band, and gain is controlled for each frequency band. A transmission signal passes as it is in a frequency band wherein the level of a transmission speech is large and an echo is suppressed in a frequency band where the level of the echo is large. Even in the double talk wherein the reception speech and a speech of a near-end speaker are both present, the echo suppressing device is provided which gives a little feeling of interruption of a speech and has high two-way communication performance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an echo suppression method and apparatus for hands-free communication such as a video conference and an audio conference.

A conventional echo suppressor will be described.
FIG. 8 is a configuration diagram of a conventional echo suppression apparatus 800 disclosed in Patent Document 1. In FIG. A conventional echo suppression apparatus 800 includes a gain multiplication unit 801, an acoustic coupling amount estimation unit 802, a transmission determination unit 803, a reception determination unit 804, and a gain control unit 805.
The echo suppression apparatus 800 suppresses an echo which is a speaker sound mixed in a microphone reception signal in a loudspeaking call using a speaker and a microphone. The input signal is a reception signal that is a reception signal from the other party, and a microphone reception signal that is received by a microphone at the local location, and the output signal is a speaker output that is a signal output from the local speaker. A signal and a transmission signal which is a transmission signal to the other party. This apparatus suppresses the echo contained in the microphone sound reception signal by multiplying the microphone sound reception signal by a gain smaller than 1 when the microphone sound reception signal mainly includes an echo to obtain a transmission signal. .
Details of this apparatus will be described below.
The acoustic coupling amount estimation unit 802 obtains an acoustic coupling amount A (t) that is an amplitude value of a transfer characteristic between the speaker and the microphone. Here, t represents a discretized time. The time average level of the speaker output signal and the microphone sound reception signal is observed, and the ratio is calculated to obtain the acoustic coupling amount. When the speaker output signal is X (t) and the microphone sound reception signal is Y (t), the acoustic coupling amount A (t) is obtained by the equation (1).
A (t) = E {| Y (t) | / | X (t) |} Equation (1)
However, E {·} represents an average time, and | · | represents an absolute value.

The transmission determination unit 803 determines transmission based on the reception signal X (t), the acoustic coupling amount A (t), and the microphone reception signal Y (t). The time smoothing level of the microphone reception signal Y (t) is observed, the time smoothing level exceeds a predetermined fixed threshold, and the time smoothing level of the reception signal X (t) is further added to the acoustic coupling amount A (t). When the estimated acoustic echo level multiplied by is over a threshold value that is a constant multiple, the transmission is determined.
The reception determination unit 804 determines reception from the reception signal. The time smoothing level of the received signal X (t) is observed, and when the level exceeds a predetermined fixed threshold value, it is determined that the received signal is received.

The gain control unit 805 controls the gain value based on the determination results of the transmission determination unit 803 and the reception determination unit 804. When the incoming call is detected and the outgoing call is not detected, only the echo is included in the microphone sound reception signal. Therefore, the preset echo suppression gain is set as the gain value. In other cases, the gain value is set to 1. In addition, time smoothing is performed so that the gain value changes smoothly in order to prevent audio deterioration due to discontinuous changes in the gain value.
The gain multiplication unit 801 multiplies the microphone sound reception signal by the gain value set by the gain control unit 805 to obtain a transmission signal.
By the above processing, the microphone sound reception signal is multiplied by a gain value less than 1 only during a period in which only the echo is included in the microphone sound reception signal, and a transmission signal in which the echo is suppressed is obtained. When the microphone sound reception signal does not include an echo or includes the voice of the near-end speaker, the microphone sound reception signal becomes a transmission signal as it is, and the transmission voice can be transmitted to the other party.
Japanese Patent No. 3082898

However, the conventional echo suppression method has a problem in double talk in which the received voice and the voice of the near-end speaker exist simultaneously. When transmission is detected during double talk, the echo is not suppressed, but is directly transmitted and transmitted to the other party, making it difficult to communicate. If the transmission is not detected, the near-end speaker's voice is suppressed and becomes a low level voice, making it difficult for the other party to hear the voice. Thus, the conventional echo suppression technology does not have sufficient two-way call performance.
An object of the present invention is to provide an echo suppression method for improving the bidirectional communication performance during double talk in which the received voice and the near-end talker voice are present simultaneously.

  An echo suppression method according to the present invention includes a first frequency domain conversion process for converting a microphone sound reception signal into a frequency domain signal composed of two or more N frequency components, and a speaker output signal having a frequency composed of N frequency domain components. The amplitude of the transfer function between the speaker and the microphone from the ratio of the second frequency domain conversion processing to convert the signal into the domain signal, the microphone sound reception signal converted into the frequency domain signal, and the speaker output signal converted into the frequency domain signal. The amount of acoustic coupling, which is the value, is estimated for each frequency domain, and the speaker output signal converted to the frequency domain signal is smoothed with a time constant corresponding to a preset reverberation time to obtain the time smoothing level. An echo level estimation process for multiplying the time smoothing level by an acoustic coupling amount to estimate the level of the echo component included in the microphone received signal for each frequency band; The microphone level estimation processing that calculates the time smoothing level of the microphone sound reception signal converted to the frequency domain signal and estimates the microphone level for each frequency band, and compares the estimated echo level with the estimated microphone level, and the estimated echo level When the estimated echo level is sufficiently low, a gain control process that sets a preset fixed gain value for each frequency band and microphone sound reception converted to a frequency domain signal are set. Gain multiplication processing that multiplies the signal with the gain value set by gain control processing for each frequency band, and inverse frequency domain transformation processing that performs inverse frequency domain transformation of the output signal multiplied by gain multiplication processing and outputs it as a transmission signal It is characterized by including.

The echo suppression method according to the present invention is further characterized in that, in the echo suppression method, the gain control processing performed for each frequency band includes a threshold obtained by multiplying an estimated echo level by a preset fixed coefficient, and an estimated microphone level. In comparison, when the estimated microphone level is smaller than the threshold value, the preset echo suppression gain is set as the instantaneous gain coefficient value. In other cases, the preset fixed value is set as the instantaneous gain coefficient value. The time-smoothed value is set for each frequency band as a gain value used in the gain multiplication process.
The echo suppression method according to the present invention further compares the estimated microphone level with a plurality of threshold values obtained by multiplying the estimated echo level by a preset fixed coefficient in the echo suppression method. If the value is smaller than the threshold value, the preset echo suppression gain corresponding to the threshold value having the value closest to the estimated microphone level among the threshold values having a value equal to or higher than the estimated microphone level is determined as the instantaneous gain coefficient value. Is characterized in that a fixed value set in advance is used as an instantaneous gain coefficient value, and a value obtained by time-smoothing these instantaneous gain coefficient values is set as a gain value used in the gain multiplication processing for each frequency band.

  The echo suppression method according to the present invention further includes microphone noise level estimation for estimating the level of stationary noise included in the microphone reception signal for each frequency domain from the microphone reception signal converted into the frequency domain signal in the echo suppression method. From the speaker output signal converted into the frequency domain signal, the received noise level estimation process for estimating the level of stationary noise included in the speaker output signal for each frequency band from the speaker output signal converted into the frequency domain signal, and the speaker output signal converted into the frequency domain signal An echo level estimation process for estimating the estimated echo level of the echo component included in the microphone received signal for each frequency band by multiplying the time smoothing level of the signal obtained by reducing the stationary noise level included in the speaker output signal by the acoustic coupling amount. Is compared with the estimated microphone level and the value obtained by multiplying the estimated echo level by a preset fixed coefficient. -When the level is high, the preset echo suppression gain is the instantaneous echo suppression gain coefficient value.In other cases, the preset fixed value is the instantaneous echo suppression gain coefficient value. The estimated microphone level is compared with a value obtained by multiplying the level by a preset fixed coefficient. If the noise level is high, the noise suppression gain instantaneous noise suppression gain coefficient value is set in advance. Otherwise, the fixed value is set in advance. Is the instantaneous noise suppression gain coefficient value, and the instantaneous echo coefficient value is the smallest value of the instantaneous echo suppression coefficient value and the instantaneous noise suppression gain coefficient value. The gain value used in the processing is set for each frequency band.

The echo suppression method according to the present invention further includes a frequency characteristic smoothing process for smoothing a gain value as an output of a gain control process performed for each frequency band on the frequency axis in the echo suppression method. The gain multiplication processing applied to the above is characterized in that the microphone sound signal converted into the frequency domain is multiplied for each frequency band by the gain value after smoothing in the frequency characteristic smoothing processing.
The echo suppression method according to the present invention further includes N ′ speaker signals having N frequency components converted into frequency domain signals by frequency domain conversion processing of the speaker output signal in the echo suppression method. The microphone sound reception signals of N frequency components converted into frequency domain signals by the frequency division conversion processing of the speaker output signal and the frequency domain conversion processing of the microphone sound reception signal are converted into N. 'None frequency band gain value of N' frequency bands, which is the output of the microphone sound reception signal to be converted into the microphone sound reception signal of the frequency component and the gain control process, and the gain value of the N frequency bands The frequency division number conversion process of the gain to be converted into is added, and the process performed for each of the N frequency bands is performed for each N ′ frequency band after the band division number conversion.

  The echo suppression method according to the present invention is further characterized in that, in the echo suppression method, the echo level estimation processing is performed by performing time smoothing with a time constant corresponding to preset M reverberation times to calculate echo levels of two or more M The gain control processing provided for each frequency band, which has an echo level calculation processing unit, compares the estimated microphone level with a value obtained by multiplying the estimated echo level corresponding to M reverberation times by a preset fixed coefficient. If the estimated echo level is high, the echo suppression gain set for each reverberation time in advance is used as the instantaneous echo suppression gain coefficient value. In other cases, the preset fixed value is set to M as the instantaneous echo suppression gain coefficient value. The instantaneous echo suppression gain coefficient is calculated by multiplying the stationary noise level included in the microphone received signal by a preset fixed coefficient and the estimated microphone level. If the noise level is high, the preset noise suppression gain is the instantaneous noise suppression gain coefficient value. Otherwise, the preset fixed value is the instantaneous noise suppression gain coefficient value, and M instantaneous echoes are used. The smallest value of the suppression gain coefficient value and the instantaneous noise suppression gain coefficient value is set as the instantaneous gain coefficient value, and a value obtained by time-smoothing the instantaneous gain coefficient value is set for each frequency band as a gain value used in the gain multiplication processing. It is characterized by that.

According to the first to fifth embodiments of the present invention described above, both the received voice and the near-end talker voice exist by giving the microphone received signal a gain for echo suppression for each band. Even in the double talk section, high-quality bidirectional communication can be performed while suppressing echo and suppressing level fluctuation of the near-end talker voice.
Furthermore, according to the second embodiment of the present invention, stationary noise such as air conditioning and a fan can be suppressed. According to the third embodiment of the present invention, discontinuous frequency characteristics can be reduced, and more natural sound quality can be realized. According to the fourth embodiment of the present invention, it is possible to reduce the number of bands to be calculated and reduce the amount of calculation. According to the fifth embodiment of the present invention, voice degradation of a near-end speaker can be minimized while sufficiently suppressing echoes even in an environment with a long reverberation time.

The echo suppressor according to the present invention is configured by hardware, and an embodiment in which the echo suppression method according to the present invention is executed by the hardware configured echo suppressor is also possible. An embodiment in which a suppression program is installed in a computer, causes the computer to function as an echo suppression device, and executes the echo suppression method according to the present invention is the best embodiment.
In order to configure the echo suppressor according to the present invention by a computer, the computer converts at least the microphone sound reception signal into a frequency domain signal composed of two or more N frequency components by an echo suppression program installed in the computer. A frequency domain converter, a second frequency domain converter for converting the speaker output signal into a frequency domain signal composed of N frequency domain components, a microphone sound signal converted into the frequency domain signal, and a frequency domain signal An acoustic coupling amount estimation unit that estimates an acoustic coupling amount, which is an amplitude value of a transfer coefficient between the speaker and the microphone, for each frequency domain based on a ratio with the speaker output signal thus obtained, and a speaker output signal converted into the frequency domain signal. The time smoothing level is obtained by smoothing with a time constant corresponding to the preset reverberation time. Echo level estimator that multiplies the acoustic coupling amount to estimate the level of the echo component contained in the microphone sound reception signal for each frequency band, and calculates the time smoothing level of the microphone sound reception signal converted to the frequency domain signal to calculate the frequency When the microphone level estimator that estimates the microphone level for each band, the estimated echo level and the estimated microphone level are compared, and the larger the estimated echo level, the larger the suppression value is set, and the estimated echo level is sufficiently low Includes a gain control unit that sets a preset fixed gain value for each frequency band, and a gain multiplication unit that multiplies the microphone sound signal converted into the frequency domain signal by the gain value set by the gain control unit for each frequency band. And an inverse frequency domain transform unit that performs inverse frequency domain transform on the output signal multiplied by the gain multiplication unit and outputs it as a transmission signal, To function as a pressure device.

Before explaining the embodiment of the present invention, an outline of the use situation of the echo suppressor according to the present invention will be described with reference to FIG. Reference numeral 700 shown in FIG. 7 denotes an echo suppressor described in each embodiment of the present invention. The input signals of the echo suppression apparatus 700 according to the present invention are a reception signal that is a reception signal from the other party and a microphone reception signal that is a signal received by the microphone M at the local point, and an output signal is a speaker at the local point. A speaker output signal that is a signal output from the SP and a transmission signal that is a transmission signal to the other party.
As shown in FIG. 7, the microphone sound reception signal includes a signal (echo) in which the speaker output sound circulates into the microphone M in addition to the near-end speaker's voice. The echo suppressor 700 suppresses this echo and facilitates conversation. Each input signal of the echo suppression apparatus 700 is converted from an analog signal to a discrete time signal by AD conversion, and each output signal is converted from a discrete time signal to an analog signal by DA conversion.
In the present invention, the microphone sound reception signal is divided into N frequency band signals, and the signal is multiplied by a gain for suppressing the echo for each frequency band to suppress the echo. However, N is an integer of 2 or more. The gain value is controlled so that the band containing a lot of echo components is suppressed by reducing the gain, and the band containing a lot of near-end speaker's voice is passed as a predetermined fixed value, for example, 1. This makes it possible to suppress the echo while suppressing the attenuation of the level of the near-end speaker's voice even in the double talk period in which the echo and the near-end speaker's voice exist simultaneously. Two-way call performance can be improved.

FIG. 1 shows a block diagram of an echo suppression apparatus 100 according to the first embodiment of the present invention. The echo suppression apparatus 100 proposed in the first embodiment of the present invention includes a first frequency domain conversion unit 101 that converts a microphone reception signal into a frequency domain signal, an inverse frequency domain conversion unit 102, and a speaker output signal that is converted into a frequency domain. a second frequency domain transform section 103 into a signal, and a gain multiplication unit ₁₀₄ 1 -104 _N, and the acoustic coupling amount estimating unit ₁₀₅ 1 to 105 _N, and the echo level estimating unit ₁₀₆ 1 - 106 _N, microphone level estimation unit 107 _{1 to} 107 _N and gain control units 108 _{1 to} 108 _N.
The first frequency domain converter 101 converts the microphone sound reception signal into a frequency domain signal having N frequency components. The conversion to the frequency domain can be performed by Fourier transform or a band division filter bank. The converted microphone reception signal is represented by Y (Ω). Here, Ω is a discrete frequency corresponding to the center frequencies ω _{0 to} ω _N−1 of the _N frequency bands in the frequency domain conversion. This frequency domain transformation is performed for each of a plurality of samples of one sample or more. An interval at which this frequency domain transformation is performed is represented as one frame. By such processing, the reception signal Y (Ω) converted into the frequency domain is obtained for each frame.

The second frequency domain conversion unit 103 that converts the speaker output signal into the frequency domain signal converts the speaker output signal into N frequency components by the same processing as the first frequency domain conversion unit 101 of the microphone reception signal. The converted speaker output signal is represented by X (Ω).
The acoustic coupling amount estimators 105 _{1 to} 105 _N provided for each frequency band are the outputs Y (Ω) of the first frequency domain conversion unit 101 for the microphone sound reception signal and the second frequency domain conversion unit 103 for the speaker output signal. An acoustic coupling amount A (Ω) for each frequency band is obtained from the output X (Ω). The acoustic coupling amount is an amplitude value of a transfer function between the speaker and the microphone, and is obtained by a ratio of an absolute value of the speaker output signal after the frequency domain conversion and the microphone sound reception signal. In addition, time smoothing is performed to improve the accuracy of the acoustic coupling amount. When the frequency domain conversion signal of the speaker output signal is X (Ω) and the frequency domain conversion signal of the microphone sound reception signal is Y (Ω), the acoustic coupling amount A (Ω) can be obtained by Expression (2).
A (Ω) = E {| Y (Ω) | / | X (Ω) |} Equation (2)
However, E {·} represents taking an average value, and | · | represents taking an absolute value.
The echo level estimation units 106 _{1 to} 106 _N provided for each frequency band include the acoustic coupling amount A (Ω) obtained by the acoustic coupling amount estimation units 105 _{1 to} 105 _N and the frequency domain conversion unit 103 of the speaker output signal. The level of the echo contained in the microphone sound reception signal is estimated from the output X (Ω) of. When the echo of the room is ignored, the echo level can be estimated by multiplying the frequency vector | X (Ω) | of the received signal by the acoustic coupling amount A (Ω). However, since the sound of the room actually exists, it is necessary to estimate the echo including the echo component. Usually, since the acoustic component of the room exponentially decays with time, the echo level R (Ω) is estimated by the following equation (3).
R (Ω) = A (Ω) ・ P (Ω)
P (Ω) = | X (Ω) | for P '(Ω) ≦ | X (Ω) |
P (Ω) = u ・ P '(Ω) + (lu) ・ | X (Ω) | for P'(Ω)> | X (Ω) | Equation (3)
However, P (Ω) is a speaker output signal after performing time smoothing corresponding to reverberation, P ′ (Ω) is P (Ω) one frame before, and u is the length of reverberation (reverberation time). ) Is a coefficient for adjusting the assumed value, and a fixed value is set in advance. For example, u has a value of 0 ≦ u <1, and the closer to 1, the longer the reverberation time is simulated, and the closer to 0, the shorter the reverberation time is simulated.

Microphone level estimation units 107 _{1 to} 107 _N provided for each frequency band are configured to output a microphone sound reception signal level (microphone level) S (Ω) from an output Y (Ω) of the first frequency domain conversion unit 101 of the microphone sound reception signal. ). The microphone level S (Ω) is obtained as an absolute value of Y (Ω). This is expressed by equation (4).
S (Ω) = | Y (Ω) | Formula (4)
Alternatively, the absolute value of Y (Ω) may be obtained by time smoothing. This is expressed, for example, by equation (5).
S (Ω) = w ・ S '(Ω) + (lw) ・ | Y (Ω) | Formula (5)
However, S ′ (Ω) is a microphone level one frame before, w is a coefficient of time smoothing, and takes a value of 0 ≦ w <1, for example. As w is closer to 1, smoothing is performed in a longer time, and as w is closer to 0, time smoothing is performed in a shorter time.
The gain controls 108 _{1 to} 108 _N provided for each frequency band were estimated by the echo level R (Ω) estimated by the echo level estimation units 106 _{1 to} 106 _N and the microphone level estimation units 107 _{1 to} 107 _N. From the microphone level S (Ω), the gain for each band given to the microphone reception signal is controlled. The gain control is performed so as to suppress the echo when the microphone reception signal contains a lot of echo components and to pass the near-end speaker voice in other cases.

First, when the echo signal contains a lot of echo components, the estimated echo level R (Ω) and the estimated microphone level S (Ω) are close to each other. When the estimated microphone level S (Ω) is smaller than a fixed value, for example, a value obtained by multiplying a fixed coefficient C of 1 or more, it is detected as a period in which many echo components are included. This condition is expressed by equation (6).
S (Ω) ≦ C ・ R (Ω) Formula (6)
If it is detected as a period in which many echo components are included, the instantaneous gain coefficient g (Ω) of that band is set to an echo suppression amount D set in advance as a fixed value. However, the echo suppression amount D takes a value of 0 ≦ D <1, for example, and the smaller the value, the more the echo suppression amount increases, but the deterioration of the near-end speaker voice during double talk increases. Next, when it is not detected as a period in which many echo components are included, the echo component is small, so the instantaneous gain coefficient g (Ω) is set to a preset fixed value, for example, 1, and the microphone sound reception signal is left as it is. Let it pass. If this gain control is expressed by an equation, equation (7) is obtained.
g (Ω) ＝ D for S (Ω) ≦ C ・ R (Ω)
g (Ω) = 1 for S (Ω)> C ・ R (Ω)
Next, the instantaneous gain coefficient g (Ω) is time-smoothed to obtain the gain G (Ω) output to the gain multipliers 104 _{1 to} 104 _N. By performing time smoothing, it is possible to suppress deterioration in sound quality due to a rapid change in gain. Time smoothing is performed, for example, as shown in Equation (8).
G (Ω) ＝ a ・ G '(Ω) + (la) ・ g (Ω) for g (Ω) ≦ G' (Ω)
G (Ω) = b · G '(Ω) + (lb) · g (Ω) for g (Ω)>G' (Ω) Equation (8)
However, G ′ (Ω) is the gain G (Ω) one frame before. a is a smoothing coefficient when the gain is lowered, b is a smoothing coefficient when the gain is raised, and is set in advance as a fixed value. a and b take values between 0 and 1, and the closer to 1, the longer the smoothing, and the closer to 0, the shorter the time.

Further, a plurality of echo suppression amounts can be set by the gain control units 108 _{1 to} 108 _N. In this case, the gain control is performed so as to increase the echo suppression amount as the microphone reception signal contains more echo components. When the echo component is not included, the near-end speaker voice is passed. Is called. As a specific example, in order to detect a period in which many echo components are included, the fixed coefficient C is set to K C _{1 to} C _K, and these coefficients C _{1 to} C _K are set to the estimated echo level R (Ω). By comparing the multiplied value with the value of the estimated microphone level S (Ω), the echo suppression amounts D _{1 to} D _K are set. That is, the instantaneous gain coefficient g (Ω) is set by the equation (9).
g (Ω) = D _K for S (Ω) ≦ C _K・ R (Ω)
g (Ω) = D _K-1 for C _K・ R (Ω) <S (Ω) ≦ C _K-1・ R (Ω)
::
g (Ω) = D ₁ for C ₂・ R (Ω) <S (Ω) ≦ C ₁・ R (Ω)
g (Ω) = 1 for S (Ω)> C ₁・ R (Ω) Equation (9)
However, the fixed coefficient _C 1 -C _K is a fixed value determined in advance, respectively, for example, take the value of 1 or greater, as the magnitude relationship coefficient is _{C 1> C 2>...>} C K, previously fixed value Set. Echo suppression amount _D 1 to D _K are each a value of 0 ≦ _{D K} ≦ 1, the magnitude relationship sets a previously fixed value such that _{D 1> D 2>...>} D K. Next, the gain G (Ω) used in the gain multipliers 104 _{1 to} 104 _N is obtained by smoothing the instantaneous gain coefficient g (Ω) over time. The time smoothing is performed by, for example, Expression (8) as described above. In this way, by setting a plurality of echo suppression amounts, the echo suppression amount can be changed according to the ratio of the echo components included in the microphone received signal, and the suppression amount is set in one step as in the prior art. Even if the echo suppression amount is increased more, it is possible to maintain the call quality during double talk.

The gain multipliers 104 _{1 to} 104 _N provided for each frequency band use the gain G (Ω) after time smoothing for each frequency band calculated by the gain control units 108 _{1 to} 108 _N as the microphone after the frequency domain. The received sound signal Y (Ω) is multiplied for each frequency band.
The inverse frequency domain transform unit 102 performs inverse frequency domain transform on the output signals of the gain multipliers 104 _{1 to} 104 _N and outputs the result as a transmission signal.
Through the above processing, the echo suppression apparatus of the present embodiment can suppress the frequency band component in which many echo components are included in the microphone received signal, and suppress the echo. In addition, since it is determined whether to suppress or pass for each frequency band, the voice of the near-end speaker at the time of double talk where the received voice and the near-end talker voice exist simultaneously than the conventional echo suppression device. Deterioration is small.
The effects of the present invention will be described with reference to the frequency spectrum diagrams of the microphone reception signal and the transmitted voice during double talk shown in FIGS. 6A, 6B, and 6C. 6A is a frequency spectrum of a microphone sound reception signal before echo suppression, and FIG. 6B is a frequency spectrum of a transmitted voice after passing through a conventional echo suppression device. Since the conventional echo suppression device inserts a loss in the full band, as shown in FIG. 6B, both the speech component and the echo component of the near-end speaker are suppressed by the same amount. For this reason, if echo suppression is performed at the time of double talk, the near-end speaker's voice included in the transmission signal becomes small and it becomes difficult to hear. On the other hand, in the frequency spectrum of the transmitted voice after passing through the echo suppressor of the present invention shown in FIG. 6C, only the frequency component having a high echo component level is suppressed, and the frequency component having a high near-end speaker speech component level is suppressed. Output as is. Thereby, the decrease in the near-end speaker voice level is smaller than that of the conventional echo suppression device.

Further, in this embodiment, the first frequency domain conversion unit 101, the reverse frequency domain conversion unit 102, and the second frequency domain conversion unit 103 of the speaker output signal are deleted without performing the frequency domain conversion. It is also possible to perform gain control in a single band. In this case, by setting a plurality of stages of echo suppression amounts as shown in Equation (9), the echo suppression amount can be changed according to the ratio of the echo components included in the microphone sound reception signal. Compared with the case where the suppression amount is set in one step as in the apparatus, the call quality during double talk can be maintained even if the echo suppression amount is increased.
As described above, according to the first embodiment of the present invention, even in the case of double talk in which both the received voice and the near-end talker voice exist, the high quality that suppresses the echo and has a low voice cut feeling. Bi-directional communication can be realized.

FIG. 2 is a block diagram of an echo suppression apparatus 200 according to the second embodiment of the present invention. The echo suppression apparatus 200 of this embodiment has a configuration in which microphone noise level estimation sections 201 _{1 to} 201 _N and reception noise levels 202 _{1 to} 202 _N are added to the first embodiment of the present invention. In this embodiment, noise can be suppressed in addition to echo suppression by estimating the noise level.
Mic noise level estimation unit 201 ₁ ~201 _N which is provided for each frequency band, from the output signal of the first frequency domain transform section 101 of the microphone received sound signals, the noise level N _S contained in the microphone received sound signals _(Omega) Is estimated. The noise estimated here is stationary noise with little temporal level fluctuation such as air conditioning or fan sound. The estimation of the noise level is performed by a dip hold process that holds the valley of the signal level with time. This dip hold is smoothed with a long time constant when the signal level is larger than the estimated noise level, and with a short time constant when the signal level is smaller than the estimated noise level. This is realized by performing smoothing. For example, the estimated noise level N _S (Ω) of the microphone sound reception signal is calculated by Expression (10).
N _S (Ω) = p ・ N _S '(Ω) + (lp) ・ S (Ω) for N _S ' (Ω) ≧ S (Ω)
N _S (Ω) = q · N _S '(Ω) + (lq) · S (Ω) for N _S ' (Ω) <S (Ω) Equation (10)
Where N ′ _S (Ω) is the estimated noise level of the microphone received signal one frame before, p is the smoothing coefficient when the estimated noise level is decreased, and q is the smoothing coefficient when the estimated noise level is increased. Yes, for example, values of 0 ≦ p <1 and 0 ≦ q <1 are set as fixed values in advance. Further, p << q is set, and the noise level is estimated by dip-holding the signal by increasing the value very slowly when the estimated noise level increases.

The reception noise level estimation units 202 _{1 to} 202 _N provided for each frequency band are processed from the output signal of the second frequency domain conversion unit 103 of the speaker output signal by the same processing as the microphone noise level estimation units 201 _{1 to} 202 _N. The reception noise level N _R that is noise included in the speaker output signal is estimated.
The echo label estimation units 106 _{1 to} 106 _N provided for each frequency band are the acoustic coupling amount A (Ω) obtained by the acoustic coupling amount estimation units 105 _{1 to} 105 _N and the second frequency domain conversion of the speaker output signal. The level of echo contained in the microphone received signal is estimated from the output X (Ω) of the unit 103 and the reception noise level N _R (Ω) estimated by the reception noise level estimation units 202 _{1 to} 202 _N. However, the echo level estimated in this embodiment is an echo level excluding the stationary noise component.

After the noise level N _R (Ω) is subtracted from the frequency spectrum | X (Ω) | of the received signal, the echo level R (Ω) is estimated by multiplying by the acoustic coupling amount A (Ω). The echo level R (Ω) is estimated by the equation (11).
R (Ω) = A (Ω) ・ P (Ω)
P (Ω) = u ・ P '(Ω) for {| X (Ω) | -r ・ N _R (Ω)} <0
P (Ω) = | X (Ω) | for P '(Ω) ≦ {| X (Ω) | -r ・ N _R (Ω)} ≧ 0
P (Ω) = u ・ P '(Ω) + (lu) ・ {| X (Ω) | -r ・ N _R (Ω)} for P'(Ω)> {| X (Ω) | -r ・N _R (Ω)} ≧ 0
Formula (11)
Here, r is a noise level subtraction coefficient, which is given fixedly in advance. For example, r = 1 is set as a standard value. If more noise level is desired to be subtracted, the value is set to 1 or more. If less noise level subtraction is desired, the value is set to 1 or less. Other symbols are the same as those in the first embodiment of the present invention, and are defined as follows. P (Ω) is a speaker output signal after time smoothing corresponding to reverberation, P ′ (Ω) is P (Ω) one frame before, and u is the length of reverberation (resonance time). A coefficient for adjusting the assumed value, and a fixed value is set in advance. For example, u has a value of 0 ≦ u <1, and the closer to 1, the longer the reverberation time is simulated, and the closer to 0, the shorter the reverberation time is simulated.
The gain controllers 108 _{1 to} 108 _N provided for each frequency band are estimated by the echo level R (Ω) estimated by the echo level estimators 106 _{1 to} 106 _N and the microphone level estimators 107 _{1 to} 107 _N. From the microphone level S (Ω) and the microphone noise level N _S (Ω) estimated by the microphone noise level estimation units 201 _{1 to} 201 _N , the gain for each band given to the microphone reception signal is controlled. The gain control suppresses echo when the microphone reception signal contains a lot of echo components, suppresses noise when noise is mainly included, and passes near-end speaker speech otherwise. To be done.

First, when the microphone received signal contains many echo components, the estimated echo level R (Ω) and the estimated microphone level S (Ω) are close to each other. For example, when the estimated microphone level S (Ω) is smaller than a value obtained by multiplying a fixed coefficient C of 1 or more, the period is detected as a period in which many echo components are included. This condition is expressed by equation (12).
S (Ω) ≦ C ・ R (Ω) Formula (12)
If it is detected as a period in which many echo components are included, the instantaneous echo suppression gain g _E (Ω) in that band is set to an echo suppression amount D set in advance as a fixed value. However, the echo suppression amount D takes a value of 0 ≦ D ≦ 1, for example, and the smaller the value, the more the echo suppression amount increases, but the deterioration of the near-end speaker voice during double talk increases. Next, when it is not detected as a period in which many echo components are included, since the echo components are small, the instantaneous echo suppression gain coefficient g _E (Ω) is set to 1, for example, and the microphone sound reception signal is passed as it is. If this gain control is expressed by an equation, equation (13) is obtained.
g _E (Ω) = D for S (Ω) ≦ C ・ R (Ω)
g _E (Ω) = 1 for S (Ω)> C ・ R (Ω) Equation (13)

Then, if it contains many noise components in microphone received sound signals, the estimated noise level N _{S (Ω)} and the estimated microphone level S (Omega) takes a value close, predetermined on the estimated noise level N _{S (Ω)} fixed value, for example, than a value obtained by multiplying one or more fixed coefficients C _N, when the estimated microphone level S (Omega) is small is detected as a period that includes many echo component. This condition is expressed by equation (14).
S (Ω) ≦ C _N · N _S (Ω) Equation (14)
When it is detected as a period that includes many noise components, the bandwidth of the instantaneous noise suppression gain factor g _E a _(Omega), it sets the noise suppression quantity D _N set in advance as a fixed value. However, the noise suppression quantity D _N takes a value of 0 ≦ D ≦ 1, although the noise suppression amount is increased enough to lower the value, increases the deterioration of the near-end speaker's speech. Next, when it is not detected as a period in which many noise components are included, the noise components are small, so the instantaneous noise suppression gain coefficient g _N (Ω) is set to a predetermined fixed value, for example, 1, and the microphone The received sound signal is passed as it is. If this gain control is expressed by an equation, equation (15) is obtained.
g _N (Ω) = D _N for S (Ω) ≦ C _N・ N _S (Ω)
g _N (Ω) = 1 for S (Ω)> C _N · N _S (Ω) Equation (15)
The smaller one of the instantaneous echo suppression gain coefficient g _E (Ω) and the instantaneous noise suppression gain coefficient g _N (Ω) obtained as described above is set as the instantaneous noise gain coefficient g (Ω). This is represented by equation (16).
g (Ω) = MIN {g _E (Ω), g _N (Ω)} Equation (16)
However, MIN {A, B} means that the smaller one of A and B is selected.

Next, as in the first embodiment of the present invention, the instantaneous gain coefficient g (Ω) is time-smoothed to obtain the gain G (Ω).
Also, a plurality of echo suppression amounts and noise suppression amounts can be set in the same manner as in the first embodiment of the present invention. A fixed coefficient C for detecting a period in which a lot of echo components are included is set to K C _{1 to} C _K, and a value obtained by multiplying the estimated echo level R (Ω) by these coefficients C _{1 to} C _K and a microphone level By comparing the values of S (Ω), the echo suppression amounts D _{1 to} D _K are set to the instantaneous echo suppression gain coefficient g _E (Ω). If this is expressed by an equation, equation (17) is obtained.
g _E (Ω) = D _K for S (Ω) ≦ C _K・ R (Ω)
g _E (Ω) = D _K-1 for C _K・ R (Ω) <S (Ω) ≦ C _K-1・ R (Ω)
::
g _E (Ω) = D ₁ for C ₂・ R (Ω) <S (Ω) ≦ C ₁・ R (Ω)
g _E (Ω) = 1 ₁ for S (Ω)> C ₁ · R (Ω) Equation (17)
Likewise instantaneous noise suppression gain factor g _N (Ω), the coefficient fixed coefficients C _N for detecting the period that includes many noise components of the J D _{N, 1} ~D _N, the _J, instantaneous echo suppression gain Coefficient g _N (Ω) is set. If this is expressed by a formula, formula (18) is obtained.
g _N (Ω) = D _{N, J} for S (Ω) ≦ C _{N, J}・ N _S (Ω)
g _N (Ω) = D _{N, J-1} for C _{N, J}・ N _S (Ω) <S (Ω) ≦ C _{N, J-1}・ N _S (Ω)
::
g _N (Ω) = D _{N, 1} for C _{N, 2}・ N _S (Ω) <S (Ω) ≦ C _{N, 1}・ N _S (Ω)
g _N (Ω) = 1 for S (Ω)> C _{N, 1} · N _S (Ω) Equation (18)
However, each of the fixed coefficients C _{1 to} C _K and C _{N, 1 to} C _{N, J} takes a value of 1 or more, and the magnitude relationship between the coefficients is C ₁ > C ₂ >...> C _K or C _{N, A} fixed value is set in advance so that ₁ > C _{N, 2} >...> C _{N, J.} The echo suppression amounts D _{1 to} D _K and the noise suppression amounts D _{N, 1 to} D _{N, J} take values of 0 ≦ D _K ≦ 1, 0 ≦ D _{N and J} ≦ 1, respectively, and the magnitude relationship is D _1. > _D 2>...> _{D K} or _{D N, 1> D N,} 2>...> D N, sets a previously fixed value such that _J. Next, the smaller one of the instantaneous echo suppression gain coefficients g _E (Ω) is selected as the instantaneous gain coefficient g (Ω), and the instantaneous gain coefficient g (Ω) is time-averaged to obtain the gain G (Ω). Time smoothing is performed in the same manner as in the first embodiment. In this way, by setting multiple echo suppression amounts and noise suppression amounts, the echo or noise suppression amount can be changed according to the ratio of the echo component and noise component contained in the microphone received signal, and the suppression amount can Even if the echo or noise suppression amount is increased rather than setting in one step as in the technology, the call quality can be maintained.
Since other parts are the same as those of the first embodiment of the present invention, description thereof is omitted.
As described above, according to the second embodiment, in addition to the effects of the first embodiment of the present invention, it is possible to suppress stationary noise such as air conditioning and fan noise.

FIG. 3 is a block diagram of an echo suppression apparatus 300 according to the third embodiment of the present invention.
The echo suppression apparatus 300 of the present embodiment has a configuration in which a frequency characteristic smoothing unit 301 is added to the first or second embodiment of the present invention. In this embodiment, the frequency characteristics of the gain are smoothed on the frequency axis, thereby reducing the discontinuous frequency characteristics and realizing a more natural sound quality.
The frequency characteristic smoothing unit smoothes the gain G (Ω) set by the gain control units 108 _{1 to} 108 _N on the frequency axis. Smoothing is performed by, for example, equation (19).
G ′ (ω _i ) = α · G ′ (ω _j−1 ) + (1-α) · G (ω _j ) (19)
However, G ′ (ω _j ) is a gain after smoothing, α is a smoothing coefficient, and a fixed value is set in advance. α takes a value of 0 ≦ α <1, for example, and the closer to 1, the stronger the smoothing.
By smoothing the frequency characteristics, it is possible to reduce the discontinuous frequency characteristics of the gain that cause unnatural sound quality, and to improve the sound quality.
Since other parts are the same as those of the first or second embodiment of the present invention, description thereof will be omitted.
As described above, according to the third embodiment, in addition to the effects of the first or second embodiment of the present invention, discontinuous frequency characteristics can be reduced, and more natural sound quality can be realized. .

スピーカ出力信号の帯域分割数変換部４０２は、マイク受音信号の帯域分割数変換部４０１と同様の処理により、スピーカ出力信号の第２周波数領域変換部１０３の出力信号である周波数領域変換後のスピーカ出力信号Ｘ（Ω）の帯域分割数をＮからＮ’に変換する。
音響結合量推定部１０５_１〜１０５_Ｎ’と、エコーレベル推定部１０６_１〜１０６_Ｎ’と、マイクレベル推定部１０７_１〜１０７_Ｎ’と、ゲイン制御部１０８_１〜１０８_Ｎ’と、マイク雑音レベル推定部２０１_１〜２０１_Ｎ’と、受話雑音レベル推定部２０２_１〜２０２_Ｎ’は、変換後の帯域分割数Ｎ’と同数あり、それぞれ帯域分割数変換後の信号を入力として、本発明の第１〜３の実施例と同様の処理を行う。 FIG. 4 is a block diagram of an echo suppression apparatus 400 according to the fourth embodiment of the present invention. The fourth embodiment of the present invention is similar to the first to third embodiments of the present invention in that the first band division conversion unit 401 for the microphone sound reception signal, the band division conversion unit 402 for the speaker output signal, and the number of gain bands A conversion unit 403 is newly provided, acoustic coupling amount estimation units 105 _{1 to} 105 _{N ′} , echo level estimation units 106 _{1 to} 106 _{N ′} , microphone level estimation units 107 _{1 to} 107 _{N ′} , and gain control unit 108. _{1 to} 108 _{N ′} , microphone noise level estimators 201 _{1 to} 201 _{N ′} , and reception noise level estimators 202 _{1 to} 202 _{N ′} are the number of band division numbers N ′ after conversion.
The microphone reception signal band division conversion unit 401 changes the frequency division number of the microphone reception signal Y (Ω) after the frequency domain conversion, which is the output signal of the first frequency domain conversion unit 101 of the microphone reception signal, from N to N. Convert to '. However, N ′ is an integer less than N, and Y (Ω) after conversion is Y ′ (Ω ′).
The conversion is performed by combining a plurality of bands before conversion into one band. For example, when converting I bands in a range of Ω = ωn,..., Ωm into one band Ω ′, The average value of the amplitudes of a plurality of bands is set as the converted amplitude. The average value is calculated by equation (20) or equation (21).

The speaker output signal band division number conversion unit 402 performs processing similar to that performed by the microphone sound reception signal band division number conversion unit 401 after frequency domain conversion, which is the output signal of the second frequency domain conversion unit 103 of the speaker output signal. The number of band divisions of the speaker output signal X (Ω) is converted from N to N ′.
Acoustic coupling amount estimation units 105 _{1 to} 105 _{N ′} , echo level estimation units 106 _{1 to} 106 _{N ′} , microphone level estimation units 107 _{1 to} 107 _{N ′} , gain control units 108 _{1 to} 108 _{N ′} , and microphone noise level estimating unit _'and, receiving the noise level estimator _{202 1 ~202 N' 201 1 ~201} N is located the same number as the number of subbands N 'after the conversion, as an input signal after band-dividing number conversion respectively, the present invention The same processing as in the first to third embodiments is performed.

The gain band division number conversion unit 403 converts the gain of the N ′ band, which is the output of the gain control units 108 _{1 to} 108 _{N ′} , into the gain of the band division number N of the frequency domain conversion unit. The conversion is performed by dividing one band before conversion into a plurality of bands. For example, when the band Ω ′ is divided into I bands of Ω = ωn,..., Ωm, the gain value of the band Ω ′ before conversion is set to the gain of the I bands Ω = ωn,. Value.
When applied to an embodiment that does not have the frequency characteristic smoothing unit 301, the gain multiplication units 104 _{1 to} 104 _N receive the gain values obtained by converting the band division number by the gain band division number conversion unit 403. And the same processing as in the first to third embodiments of the present invention is performed.
When applied to the embodiment having the frequency characteristic smoothing unit 301, the frequency characteristic smoothing unit 301 receives the gain value obtained by converting the band division number by the gain band division number conversion unit 403 as an input, and The same processing as in the first to third embodiments is performed.
Since other parts are the same as those in the first to third embodiments of the present invention, description thereof is omitted.
As described above, according to the present embodiment, in addition to the effects of the first to third embodiments of the present invention, the amount of calculation can be reduced by reducing the number of band divisions in some processes. Can do.

FIG. 5 is a diagram showing an echo level estimator of an echo suppressor that is the fifth embodiment of the present invention.
In the echo suppression apparatus of this embodiment, the echo level estimation unit 106 _i (i = 1,..., N) included in the first to fourth embodiments of the present invention has a plurality of reverberations as shown in FIG. It is characterized by comprising echo level calculation units 106 _{i, 1 to} 106 _{i, M} corresponding to time. By assuming a plurality of reverberation times and estimating a plurality of echo levels R ₁ (Ω) to R _M (Ω), an echo suppression amount corresponding to the reverberation time can be set.
The echo level estimation unit 106 _i (i = 1,..., N) estimates the echo level in the same manner as the echo level estimation units 106 _{1 to} 106 _{N according} to the first to fourth embodiments of the present invention. However, M values (u _{1 to} u _M ) are set as coefficients u for adjusting the expected value of reverberation length (reverberation time), and each echo level calculation unit 106 _{i, 1 to} 106 _{i, M} The echo levels R ₁ (Ω) to R _M (Ω) are calculated when each reverberation time is assumed.
The gain control units 108 _{i to} 108 _N provided for each frequency band include echo levels R ₁ (Ω) to R _M (Ω) estimated by the echo level estimation units 106 _{i to} 106 _N and a microphone level estimation unit 107. and _i to 107 _N in the estimated microphone level S (Omega), the microphone noise level estimation unit ₂₀₁ i _~201 microphone noise level estimated by the _{N N S (Ω),} each band providing the microphone level received sound signal To control the gain. The instantaneous noise suppression gain coefficient g _N (Ω) is obtained in the same manner as in the first to fourth embodiments of the present invention. Instantaneous echo suppression gain coefficients are also obtained in the same manner as in the first to fourth embodiments of the present invention, but a plurality of estimated echo levels R ₁ (Ω) to R _M (Ω) assuming a plurality of reverberation times, For each, an instantaneous echo suppression gain coefficient g _{E, 1} (Ω) to g _{E, M} (Ω) is obtained. Among these instantaneous echo suppression gain coefficients and instantaneous noise suppression gain coefficients, the smallest gain value is selected by the minimum gain selection section 108-1, and the selected gain coefficient is set as the instantaneous suppression gain coefficient g (Ω). suppression gain factor g of (Omega) (as in examples 1 to 4) time smoothing unit time smoothing with 108-2, and outputs the gain multiplication unit ₁₀₄ 1 -104 _N.

Here, the set values D and D _{1 to} D _K of the echo suppression amount are set for each assumed reverberation time. In general, the magnitude of echo attenuates exponentially with time due to the reverberation characteristics of the room. Therefore, a higher echo suppression amount is set as the expected reverberation time is shorter, and the echo suppression amount is decreased as the reverberation time is shorter, so that a constant reverberation echo level can be obtained with respect to reverberation. This eliminates excessive cancellation of echoes and minimizes near-end speaker speech degradation.
Further, in this embodiment, the first frequency domain conversion unit 101, the reverse frequency domain conversion unit 102, and the second frequency domain conversion unit 103 of the speaker output signal are deleted without performing the frequency domain conversion. It is also possible to perform gain control for all bands at once. Also in this case, as in the first embodiment, by setting a plurality of echo suppression amounts as shown in the equation (9), the echo suppression amount can be changed depending on the ratio of the echo component included in the microphone received signal. As compared with the case where the suppression amount is set in one step as in the conventional echo suppression device, the call quality during double talk can be maintained even if the echo suppression amount is increased.

Since other parts are the same as those in the first to fourth embodiments of the present invention, description thereof will be omitted.
As described above, according to the fifth embodiment, in addition to the effects of the first to fourth embodiments of the present invention, the near-end talk is performed while suppressing the echo sufficiently even in an environment with a long reverberation time. The voice degradation of the person can be minimized.
The echo suppressor according to the present invention described in each of the above embodiments is an echo suppressor described above by installing an echo suppression program described in a computer-readable program language in a computer and causing a CPU provided in the computer to decode the program. And the echo suppression method according to the present invention is executed.
The echo suppression program according to the present invention is recorded in a computer-readable recording medium such as a magnetic disk, CD-ROM, or semiconductor memory. The computer can be installed from these recording media or can be installed through a communication line.

  The echo suppression method and apparatus according to the present invention is utilized in the field of hands-free communication such as a video conference system or an audio conference system.

The block diagram for demonstrating the echo suppression apparatus which is the 1st Example of this invention. The block diagram for demonstrating the echo suppression apparatus which is the 2nd Example of this invention. The block diagram for demonstrating the echo suppression apparatus which is the 3rd Example of this invention. The block diagram for demonstrating the echo suppression apparatus which is the 4th Example of this invention. The block diagram for demonstrating the echo suppression apparatus which is the 5th Example of this invention. A is a diagram showing an inserted / received speech spectrum before passing through the echo suppressor, B is a diagram showing a transmitted speech spectrum after passing through the conventional echo suppressor, and C is a transmitted speech spectrum after passing through the echo suppressor of the present invention. FIG. The figure for demonstrating the usage of the echo suppression apparatus by this invention. The block diagram for demonstrating the conventional echo suppression apparatus.

Explanation of symbols

101 1st frequency domain transforming unit 102 Inverse frequency domain transforming unit 103 2nd frequency domain transforming unit 104 _{1 to} 104 _N gain multiplication unit 105 _{1 to} 105 _N acoustic coupling amount estimation unit 106 _{1 to} 106 _N echo level estimation unit
107 _{1 to} 107 _N microphone level estimation unit 108 _{1 to} 108 _N gain control unit 201 _{1 to} 201 _N microphone noise level estimation unit 202 _{1 to} 202 _N reception noise level estimation unit 301 frequency characteristic smoothing unit 401 to 403 Band division number conversion Part

Claims (16)

A first frequency domain conversion process for converting a microphone sound reception signal into a frequency domain signal composed of two or more N frequency components;
A second frequency domain conversion process for converting the speaker output signal into a frequency domain signal composed of N frequency domain components;
From the ratio of the microphone sound signal converted to the frequency domain signal and the speaker output signal converted to the frequency domain signal, the acoustic coupling amount, which is the amplitude value of the transfer function between the speaker and the microphone, is determined for each frequency domain. Acoustic coupling amount estimation processing to be estimated;
The speaker output signal converted into the frequency domain signal is smoothed with a time constant corresponding to a preset reverberation time to obtain a time smoothing level, and this time smoothing level is multiplied by the acoustic coupling amount and included in the microphone sound reception signal. Echo level estimation processing for estimating the level of echo components to be generated for each frequency band,
A microphone level estimation process for calculating a time smoothing level of the microphone reception signal converted into the frequency domain signal and estimating a microphone level for each frequency band;
The estimated echo level is compared with the estimated microphone level, and a gain value with a large suppression amount is set as the estimated echo level increases. When the estimated echo level is sufficiently small, a preset fixed gain value is set for each frequency band. Gain control processing to be set to
Gain multiplication processing for multiplying the microphone sound signal converted into the frequency domain signal by the gain value set in the gain control processing for each frequency band;
An inverse frequency domain transform process for performing an inverse frequency domain transform on the output signal multiplied by the gain multiplication process, and outputting as a transmission signal;
Including an echo suppression method.   2. The echo suppression method according to claim 1, wherein the gain control processing performed for each frequency band compares a threshold obtained by multiplying the estimated echo level by a preset fixed coefficient and the estimated microphone level. When the estimated microphone level is smaller than the threshold value, a preset echo suppression gain is used as an instantaneous gain coefficient value. In other cases, a preset fixed value is used as an instantaneous gain coefficient value. An echo suppression method, wherein a time-smoothed value is set for each frequency band as a gain value used in the gain multiplication process.   The echo suppression method according to claim 1, wherein a plurality of threshold values obtained by multiplying the estimated echo level by a preset fixed coefficient are compared with the estimated microphone level, respectively, and the estimated microphone level is any threshold value. Is smaller than the estimated microphone level, a preset echo suppression gain corresponding to a threshold having a value closest to the estimated microphone level is determined as an instantaneous gain coefficient value, In this case, an echo suppression method characterized in that a fixed value set in advance is used as an instantaneous gain coefficient value, and a value obtained by time-smoothing these instantaneous gain coefficient values is set as a gain value used in the gain multiplication processing for each frequency band. The echo suppression method according to any one of claims 1 to 3, wherein a microphone noise is estimated for each frequency domain from a microphone reception signal converted into the frequency domain signal. Level estimation process,
From the speaker output signal converted into the frequency domain signal, a reception noise level estimation process for estimating the level of stationary noise included in the speaker output signal for each frequency band;
Estimating an echo component included in the microphone sound reception signal by multiplying the time smoothing level of the signal obtained by subtracting the stationary noise level included in the speaker output signal from the speaker output signal converted into the frequency domain signal by the acoustic coupling amount Echo level estimation processing for estimating the echo level for each frequency band;
A value obtained by multiplying the estimated echo level by a preset fixed coefficient and the estimated microphone level are compared. If the estimated echo level is large, a preset echo suppression gain is set as an instantaneous echo suppression gain coefficient value. In this case, a preset fixed value is used as an instantaneous echo suppression gain coefficient value, and a value obtained by multiplying a stationary noise level included in the microphone received signal by a preset fixed coefficient is compared with the estimated microphone level. If the level is high, the noise suppression gain is set to a preset instantaneous noise suppression gain coefficient value. Otherwise, the preset fixed value is set to the instantaneous noise suppression gain coefficient value, and the instantaneous echo suppression gain coefficient value and the instantaneous noise are set. The smallest value among the suppression gain coefficient values is used as the instantaneous gain coefficient value, and the gain obtained by using the time-smoothed value of the instantaneous gain coefficient value in the gain multiplication process. Echo suppressing method and setting for each frequency band as.   The echo suppression method according to any one of claims 1 to 5, further comprising: a frequency characteristic smoothing process for smoothing a gain value as an output of a gain control process performed for each frequency band on a frequency axis, The gain multiplication process performed for each frequency band is characterized in that the microphone sound signal converted into the frequency domain is multiplied for each frequency band by the gain value smoothed in the frequency characteristic smoothing process. Echo suppression method. 5. The echo suppression method according to claim 1, wherein a speaker signal having N frequency components converted into a frequency domain signal by frequency domain conversion processing of the speaker output signal is equal to or greater than 2 and less than N. 'Band division number conversion processing of speaker output signal to convert into speaker output signal of frequency components,
Band division of microphone sound reception signal for converting microphone sound reception signal of N frequency components converted to frequency domain signal by frequency domain conversion processing of the microphone sound reception signal into microphone sound reception signal of N ′ frequency components Number conversion processing,
A gain band division number conversion process for converting the gain values of N ′ frequency bands, which are the outputs of the gain control process, into gain values of N frequency bands;
An echo suppression method characterized in that the processing performed for each of the N frequency bands is performed for each of N ′ frequency bands after the band division number conversion. The echo suppression method according to any one of claims 1 to 6, wherein the echo level estimation processing is performed by performing time smoothing with a time constant corresponding to preset M reverberation times to calculate an echo level. Echo level calculation processing unit,
The gain control processing provided for each frequency band compares the estimated microphone level with a value obtained by multiplying the estimated echo level corresponding to the M reverberation times by a preset fixed coefficient, and the estimated echo level is If it is large, the echo suppression gain set in advance for each reverberation time is used as the instantaneous echo suppression gain coefficient value. Otherwise, a preset fixed value is used as the instantaneous echo suppression gain coefficient value, and M instantaneous echo suppression gain coefficients are used. And comparing the estimated microphone level with a value obtained by multiplying the stationary noise level included in the microphone received signal by a preset fixed coefficient, and if the noise level is large, the preset noise suppression gain is set to the instantaneous noise level. In other cases, a fixed value set in advance is used as an instantaneous noise suppression gain coefficient value, and the M instantaneous echo suppression gains are set. The smallest value of the coefficient value and the instantaneous noise suppression gain coefficient value is set as an instantaneous gain coefficient value, and a value obtained by time-smoothing the instantaneous gain coefficient value is set as a gain value used in the gain multiplication processing for each frequency band. An echo suppression method characterized by the above. A first frequency domain converter that converts a microphone sound reception signal into a frequency domain signal composed of two or more N frequency components;
A second frequency domain converter that converts the speaker output signal into a frequency domain signal composed of N frequency domain components;
From the ratio of the microphone sound signal converted to the frequency domain signal and the speaker output signal converted to the frequency domain signal, the acoustic coupling amount, which is the amplitude value of the transfer function between the speaker and the microphone, is determined for each frequency domain. An acoustic coupling amount estimation unit to be estimated;
The speaker output signal converted into the frequency domain signal is smoothed with a time constant corresponding to a preset reverberation time to obtain a time smoothing level, and this time smoothing level is multiplied by the acoustic coupling amount and included in the microphone sound reception signal. An echo level estimator for estimating the level of echo components to be generated for each frequency band;
A microphone level estimation unit that calculates a time smoothing level of the microphone reception signal converted into the frequency domain signal and estimates a microphone level for each frequency band;
The estimated echo level is compared with the estimated microphone level, and a gain value with a large suppression amount is set as the estimated echo level increases. When the estimated echo level is sufficiently small, a preset fixed gain value is set for each frequency band. A gain control unit to be set to
A gain multiplier that multiplies the microphone sound signal converted into the frequency domain signal by a gain value set by the gain controller for each frequency band;
An inverse frequency domain transform unit that performs an inverse frequency domain transform on the output signal multiplied by the gain multiplier, and outputs the signal as a transmission signal;
An echo suppressor comprising:   9. The echo suppression apparatus according to claim 8, wherein the gain control unit provided for each frequency band compares a threshold obtained by multiplying the estimated echo level by a preset fixed coefficient and the estimated microphone level. When the estimated microphone level is smaller than the threshold value, a preset echo suppression gain is used as an instantaneous gain coefficient value. In other cases, a preset fixed value is used as an instantaneous gain coefficient value. An echo suppression apparatus, wherein a time-smoothed value is set for each frequency band as a gain value used in the gain multiplication unit.   9. The echo suppression apparatus according to claim 8, wherein the estimated microphone level is compared with a plurality of threshold values obtained by multiplying the estimated echo level by a plurality of coefficients having a preset value equal to or greater than a preset fixed value. When the estimated microphone level is smaller than any threshold, a preset echo suppression gain corresponding to a threshold having a value closest to the estimated microphone level among thresholds having a value equal to or higher than the estimated microphone level Is set as an instantaneous gain coefficient, otherwise a preset fixed value is set as an instantaneous gain coefficient, and a value obtained by time-smoothing these instantaneous gain coefficients is set as a gain value used in the gain multiplication processing for each frequency band. An echo suppressor characterized by. 11. The echo suppression apparatus according to claim 8, wherein a microphone noise for estimating a stationary noise level included in a microphone sound reception signal for each frequency domain from the microphone sound reception signal converted into the frequency domain signal. A level estimator;
From the speaker output signal converted into the frequency domain signal, a reception noise level estimation unit that estimates the level of stationary noise included in the speaker output signal for each frequency band;
Estimating an echo component included in the microphone sound reception signal by multiplying the time smoothing level of the signal obtained by subtracting the stationary noise level included in the speaker output signal from the speaker output signal converted into the frequency domain signal by the acoustic coupling amount An echo level estimator for estimating the echo level for each frequency band;
A value obtained by multiplying the estimated echo level by a preset fixed coefficient and the estimated microphone level are compared. If the estimated echo level is large, a preset echo suppression gain is set as an instantaneous echo suppression gain coefficient value. In this case, a preset fixed value is used as an instantaneous echo suppression gain coefficient value, and a value obtained by multiplying a stationary noise level included in the microphone received signal by a preset fixed coefficient is compared with the estimated microphone level. If the level is large, it is set as a preset noise suppression gain instantaneous noise suppression gain coefficient; otherwise, a preset fixed value is set as an instantaneous noise suppression gain coefficient value, and the instantaneous echo suppression gain coefficient value and the instantaneous noise suppression The smallest value among the gain coefficient values is used as the instantaneous gain coefficient value, and a value obtained by smoothing the instantaneous gain coefficient value with time is used in the gain multiplication process. Echo suppressing apparatus characterized by setting for each frequency band by.   12. The echo suppression device according to claim 8, further comprising: a frequency characteristic smoothing unit that smoothes a gain value serving as an output of a gain control unit provided for each frequency band on a frequency axis, and the frequency The gain multiplication unit provided for each band multiplies the microphone sound signal converted into the frequency domain signal by the gain value smoothed by the frequency characteristic smoothing unit for each frequency band. Echo suppression device. 13. The echo suppression device according to claim 8, wherein N speaker components having N frequency components converted into a frequency domain signal by a frequency domain converter of the speaker output signal are equal to or greater than 2 and less than N. 'Speaker output signal band division number conversion unit for converting into speaker output signal of frequency components,
Band division of a microphone sound reception signal for converting a microphone sound reception signal of N frequency components converted into a frequency domain signal by a frequency domain conversion unit of the microphone sound reception signal into a microphone sound reception signal of N ′ frequency components A number converter,
A gain band division number conversion unit for converting the gain values of N ′ frequency bands, which are the outputs of the gain control unit, into gain values of N frequency bands;
An echo suppressor characterized in that the processing performed for each of the N frequency bands is performed for each N ′ frequency band after the band division number conversion. 14. The echo suppression device according to claim 8, wherein the echo level estimation unit calculates the echo level by performing time smoothing with a time constant corresponding to preset M reverberation times. Have echo level calculators,
The gain controller provided for each frequency band compares the estimated microphone level with a value obtained by multiplying the estimated echo level corresponding to the M reverberation times by a preset fixed coefficient, and the estimated echo level is If it is large, the echo suppression gain set in advance for each reverberation time is used as the instantaneous echo suppression gain coefficient value. Otherwise, a preset fixed value is used as the instantaneous echo suppression gain coefficient value, and M instantaneous echo suppression gain coefficients are used. And comparing the estimated microphone level with a value obtained by multiplying the stationary noise level included in the microphone received signal by a preset fixed coefficient, and if the noise level is large, the preset noise suppression gain is set to the instantaneous noise level. In other cases, a fixed value set in advance is used as an instantaneous noise suppression gain coefficient value, and the M instantaneous echo suppression gains are set. The smallest value among the numerical value and the instantaneous noise suppression gain coefficient value is set as an instantaneous gain coefficient value, and a value obtained by time-smoothing the instantaneous gain coefficient value is set as a gain value used in the gain multiplier for each frequency band. Echo suppression device.   An echo suppression program written in a computer-readable program language and causing the computer to execute the echo suppression method according to claim 1.   A recording medium comprising a computer-readable recording medium, wherein the echo suppression program according to claim 15 is recorded on the recording medium.

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