JPS61121625A - Echo signal erasing device - Google Patents

Abstract

PURPOSE:To expand the range of application by allowing an attenuation controller to give an echo signal cancelling amount suitable for surrounding noises while using S/N estimated from power for a short time and increasing the attenuation of an attenuator of an estimated band. CONSTITUTION:Echo cancellers 341-34n estimate an echo signal included in each bans signal of the 1st band splitter 32 based on each band signal of the 1st band splitter 32 and each band signal of the same band of the 2nd band splitte 33 and obtain each band signal erasing an echo signal by subtracting each estimated band signal of the echo signal from each band signal of the 1st band splitter 32. On the other hand, short-time power calculation devices 371-37n calculate a short-time power pj of a band signal xj at a time (j) obtained from the 1st band splitter 32 according to an equation I. An attenuation controller 38 controls the attenuation of the attenuators 351-35n based on the short-time power of each band signal obtained by the equation I.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used in teleconferencing systems and loudspeaker telephones to eliminate echo signals generated due to acoustic coupling between speakers and microphones, and to suppress howling. (No change in content) This relates to an echo signal canceling device that uses pressure.

Conventional technology In recent years, with the development of teleconferencing systems that connect remote points,
In the above system, a reverberant signal canceling device is attracting attention as a means for canceling a reverberant signal generated by acoustic coupling between a speaker and a microphone and suppressing howling. Conventionally, the example is ``Literature ``A Design of Canceller 7 O Broadband Acoustic/X Co.''
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P P, 232-239 (Mupri11984
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The conventional echo signal canceling device as described above will be described below with reference to the drawings.

FIG. 7 is a diagram showing a communication conference system using a conventional echo signal canceling device. In FIG.
8 is a speaker, 9 is a 10H microphone, 11 is a speaker, 12 is a speaker B, 13 is a conference room, and 14 is a conference room B.

The voice spoken by the speaker 110 in the conference room 13 is transmitted from the microphone 9 to the speaker 8 via the amplifier 3 and the amplifier 6. The audio signal output from the speaker 8 of the conference room B14 is transmitted to the speaker B12, and at the same time is transmitted to the amplifier 5. It returns to the speaker 11 through the amplifier 6 as a reverberation signal delayed by the propagation delay time of the signal from the speaker 7j. The return of such echo signals disrupts natural conference calls. Furthermore, since the audio signal output from the speaker 7 also goes around to the microphone 9, the audio signal spoken by the speaker M forms a loop. If this loop gain exceeds 1, howling will occur, which will greatly disturb the sound of a conference call. Therefore, in the communication conference system shown in Fig. 7, the echo signal canceling device 1, 2t is used.
- By using it, echo signals are canceled and howling is suppressed. That is, the echo signal of the speaker 11 is canceled by the echo signal canceling device 2 on the far end side of the speaker 11,
By canceling the echo signal of the speaker B12 with the echo signal canceling device 1 located on the far end side of the speaker B12, it is possible to realize a communication conference system that allows two-way conference calls with natural sound quality.

An example of an echo signal canceling device used in such a teleconferencing system is a device with a sampling frequency of 161C2,
Considering the case where the echo signal duration is 250 ms, the number of filter taps is required to be 4,000. In order to process a filter with such a large number of taps in real time, it is necessary to divide the processing, and a band-splitting echo canceller is required. A similar echo signal cancellation device is proposed in the above-mentioned document. The advantage of using a band-splitting echo canceller is that it divides the input signal into frequency bands and then converts it to a lower frequency, making it possible to perform the same processing on signals in each band. be.

FIG. 8 shows a configuration diagram of a conventional echo signal canceling device using the above-mentioned band division type echo canceller. In FIG. 8, 16 is a receiving side input signal terminal, 1e is a receiving side output signal terminal, 1 is a transmitting side input signal terminal, 18 is a transmitting side output signal terminal, and 19 is a plurality of (n) transmitting side input signals. 2o is a second band divider that divides the receiving side input signal into n frequency bands having the same characteristics as the first band divider; 211 to 11n are Each band obtained by the first band splitter based on each band signal obtained by the first band splitter and each band signal of the same band obtained by the second band splitter. echo canceller that cancels echo signals included in the signal;
Reference numeral 22 denotes a band synthesizer that synthesizes the respective band signals whose echo signals have been canceled by the echo canceller to create a transmitting side output signal in which echo signals have been completely canceled. FIG. 9 is an internal configuration diagram of the echo canceller. In Figure 9, 23
24 is a band signal terminal for the input signal on the receiving side, 26 is a band signal terminal for the output signal on the sending and receiving side, and 26 is the band signal terminal for the input signal on the receiving side and the human input signal on the sending side. 27 is an adaptive filter consisting of a variable coefficient transversal filter for creating an estimated band signal of the echo signal included in the band signal of the transmitting side input signal based on the band signal of the transmitting side input signal; This is a subtracter that creates a band signal of the transmitter output signal in which the echo signal has been eliminated by subtracting the estimated band signal of the echo signal from the subtracter.

The operation of the echo signal canceling device configured as above will be described below.

First, a transmitting side input signal and a receiving side input signal are divided into n frequency bands by a first band divider 19 and a second band divider 2°, respectively, to obtain band signals. Next, the echo canceller 211 estimates the echo signal included in each band signal of the input signal on the transmitting side, and estimates each estimated band signal of the echo signal from each band signal of the input signal on the transmitting side. By subtracting , each band signal of the transmitting side output signal with the echo signal canceled is obtained. Next, each band signal of the transmitting side output signal from which the echo signal has been removed is sent to a band synthesizer 22.
Create a transmitter output signal with the echo signal removed by combining the signals using

Next, using FIG. 9, echo cancellers 211 to 21
The internal operation of n will be explained. echo canceller 2
In steps 11 to 21n, an adaptive filter 26 is used to filter the signal between the speaker and the microphone (strictly speaking, the band signal of the receiving side input signal hlj (corresponding to the filter coefficient of the adaptive filter) between the terminal 23 and the band signal terminal 24 of the transmitting side input signal
(i = 1.2 +..., N, N is the number of impulse response samples), the estimated impulse response (△ represents the estimated value) and the receiving side input signal Convolve with the band signal of , as shown in Equation (1) (
(filtering using the filter coefficients) to create an estimated band signal 1j of the echo signal.

Next, the subtracter 27 is used to subtract the estimated band signal of the echo signal from the band signal of the human input signal on the receiver side as shown in equation (2), so that the band signal of the transmitter output signal from which the echo signal has been eliminated is ej(i-create.

'j = ”j −'j ”゛”°“−°−(
2) The impulse response is estimated when the input signal on the transmitting side is caused only by the echo signal of the human input signal on the receiving side, that is, when only the speaker at the far end is speaking as seen from the echo signal canceling device. Estimating the impulse response can be done, for example, at the first (
The impulse response is corrected for each sample period according to the Al-7' IJ rhythm of the learning identification method shown in Equation 31.

・・・・・・・・・(3) However, α is a constant of 0<α<2.

As described above, in a conference call system using the echo signal canceling device, it is possible to conduct a natural conference call in which echo signals are eliminated.

Problems to be Solved by the Invention However, the above configuration has the following problems.

In general, the indoor ambient noise level is high in the low frequency region and decreases in the high frequency region, as shown in FIG. 10 (&). In the algorithm based on the learning identification method, the amount of echo signal cancellation is when the signal-to-noise ratio is 1 s/N (dB). AN
C (dB) is given by Equation (41).

Mu CANC=S/N+1o1oq. (2/a-1)
(4) Ambient noise acts as noise, so the echo signal level in a room with the indoor noise characteristics shown in Figure 10 (al) is the same as before and when the echo signal canceller was operated. later 1st
The problem is that in the conventional configuration, the amount of echo signal cancellation varies depending on the frequency, and the howling margin is determined by the lowest amount of echo signal cancellation, so the howling margin cannot be large. There was a point.

Furthermore, in conventional echo signal canceling devices, howling may occur if the direction of the microphone is completely changed and the acoustic coupling characteristics between the speaker and the microphone are suddenly and significantly changed.

Conventionally, these problems have been dealt with by imposing restrictions on usage, usage environment, etc.

In view of the above-mentioned problems, the present invention provides a reverberant signal canceling device that can be used in a wide range of applications by easing restrictions on the usage environment by improving the howling margin against changes in the environment.

Means for Solving All Problems In order to solve the above-mentioned problems, the echo signal canceling device of the present invention has a first method that divides the input signal on the transmitting side into a plurality of frequency bands.
a second band divider that divides the receiving side input signal into a plurality of frequency bands having the same characteristics as the first band divider, and each band obtained by the first band divider. an echo canceler that cancels echo signals included in each band signal obtained by the first band splitter based on the signal and each band signal of the same band obtained by the second band splitter; an attenuator that attenuates each band signal from which the echo signal has been canceled by the echo canceller; and a band synthesizer that combines the band signals attenuated by the attenuator to create a transmitter output signal from which the echo signal has been canceled. and a short-time power calculator that calculates the total short-time power of each band signal obtained by the first band divider, and a short-time power calculator that calculates the short-time power of each band signal obtained by the short-time power calculator. and an attenuation amount controller that controls the amount of attenuation of the attenuator.

Effect of the present invention With the above-described configuration, the attenuation controller estimates the signal-to-noise ratio of each band signal from the short-time power of each band signal obtained by the first band divider, and calculates the estimated signal. By controlling the amount of attenuation of the attenuator based on the noise-to-noise ratio, the amount of echo signal cancellation adapted to the ambient noise level is provided. By estimating the occurring frequency and controlling the attenuator to increase the amount of attenuation in the estimated band, if howling occurs, it can be suppressed immediately, reducing the howling margin against environmental changes. can be improved.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of an echo signal canceling device in one embodiment of the present invention.

In FIG. 1, 28 is a receiving side input signal terminal, 29 is a receiving side output signal terminal, 30 is a transmitting side input signal terminal, 31 is a transmitting side output signal terminal, and 32 is a plurality of transmitting side input signals (n
33 is a second band divider that divides into n frequency bands having the same characteristics as the band divider 32 of the receiving side output signal terminal 1; 341 to 3;
4n is obtained by the first band divider 32 based on each band signal obtained by the first band divider 32 and each band signal of the same band obtained by the second band divider 33. an echo canceller for canceling echo signals included in each band signal; 361 to 35n are attenuators for attenuating each band signal from which the echo echo signal has been completely canceled in each echo canceller;
36 is a band synthesizer which synthesizes each band signal attenuated by each of the above-mentioned attenuators to create a transmission side output signal in which echo signals are eliminated; 371 to 37n are first band dividers 32;
A short-time power calculator 38 calculates the short-time power of each band signal obtained by the short-time power calculator, and 38 calculates the attenuation amount of each attenuator based on the short-time power of each band signal obtained by the short-time power calculator. This is an attenuation amount controller that controls.

The operation of the echo signal canceling device configured as above will be described below.

First, using the first band divider 32 and the second band divider 33, respectively, the input signal on the transmitting side and the human input signal on the receiving side are divided into n frequency bands as shown in FIG. 2 to obtain a band signal. . In FIG. 2, CHl to CHn represent n frequency-divided band signals.

FIG. 3 shows a diagram of the internal configuration of the first and second band splitters. In FIG. 3, 39 is an input signal terminal, 40 is a low-pass filter, and 41 is an analog-to-digital converter (hereinafter referred to as a MU/D converter).

421 to 42n are band pass filters, 431 to 43n are low frequency converters, and 441 to 44n are band signal output terminals. The internal operation of the band divider will be explained using FIG.

The input signal of the band divider is band-limited to a low frequency by a low-pass filter 4°, and then converted into a digital signal by a MU/D converter 41.

Next, the input signal converted into a digital signal is passed through n bandpass filters 421 to 42n having characteristics as shown in FIG.
Perform frequency band division by passing 'i,
By converting to a low frequency in the next low frequency converters 431 to 43n and then downsampling, all n band signals (more precisely, band signals converted to a low frequency) are obtained.

Next, the echo cancellers 341 to 34n generate the first signal based on each band signal of the first band splitter 32 and each band signal of the same band of the second band splitter 33 obtained as described above. Each band signal in which the echo signal contained in each band signal of the band divider 32 is estimated and the echo signal is eliminated by subtracting each estimated band signal of the echo signal from each band signal of the first band divider 32. get. The internal operation of the echo canceller is the same as that described in the prior art.

Next, the attenuators 351 to 35n attenuate each band signal whose echo signals have been completely canceled by the echo cancellers 341 to 34n, respectively, by an amount specified by the attenuation amount controller 38.

The band synthesizer 36 synthesizes the band signals attenuated by the attenuators 351 to 35H to create a transmitter output signal from which echo signals have been eliminated.

FIG. 4 shows an internal configuration diagram of the band synthesizer 36.

In FIG. 4, 451 to 45n are band signal input terminals;
461 to 46n are high frequency converters, 471 to 47n are band pass filters having the same characteristics as the band pass filter of the band divider, 48 is an adder, 49 is a digital to analog converter (hereinafter referred to as D/MUCO/verter), 6o is a low-pass filter, and 31 is a transmitting side output signal terminal. The internal operation of the band synthesizer will be explained using FIG.

First, each band signal input to the band synthesizer 36 is up-sampled by high-frequency converters 461 to 46n, then converted to a high frequency, and then passed through the next band pass filters 471 to 47n.
After extracting the necessary band signal components in the adder 48, the adder 48 adds the band signals, thereby synthesizing the transmitting side output signal.

The D/mu converter 49 converts the transmitting side output signal of the digital signal synthesized as described above into an analog signal, and after removing unnecessary high frequency signal components with the low pass filter 6o, the transmitting side output signal terminal 31 Output to.

On the other hand, the short-time power calculators 371 to 37n calculate the short-time power pj of the band signal X at time j obtained by the first band divider 32 according to equation (5).

However, M is the number of samples in the section in which the short-time power is calculated.

The attenuation amount controller 38 controls the attenuators 361 to 35n based on the short-time power of each band signal obtained as described above.
The attenuation amount is controlled.

The operation of the attenuation amount controller 38, that is, a specific method of controlling the attenuators 351 to 35n from the short-time power of each band signal will be described below.

Attenuators 361-35ni from the short-time power of each band signal
The first method of control is to estimate the signal-to-noise ratio of each band signal from the short-time power of the band signal, and then, based on the estimated signal-to-noise ratio, control the signal-to-noise ratio for the band signal with a low signal-to-noise ratio. This is to control the attenuators 351 to 35n'i so as to provide a larger amount of attenuation compared to a band signal with a high signal-to-noise ratio.

One method for estimating the total signal-to-noise ratio from the short-time power of a band signal on which noise is superimposed will be described with reference to FIG. In Figure 5, (&) is the short-term power level of noise, (bl is the short-term power level of voice, cl is the short-term power level of voice + noise, and the time of each band signal. FIG.

As shown in Figure 6(b), there are always silent intervals in speech, so when the noise level is steady as shown in Figure 5 (ILI), The average value of a certain number of short-term power levels of a voice signal with superimposed noise over a certain period of time (for example, from O, S seconds to 2 seconds) taken in order from the smallest. Estimated value of the short-term power level of total noise. PN, then the short-time power level Ps+ of the signal on which noise is superimposed, and the estimated value P3 of the short-time power level of the signal component is given by equation (6).

As described above, the signal-to-noise ratio of each band signal is estimated from the short-time power of each band signal, and for band signals with a low signal-to-noise ratio and a small amount of echo signal cancellation by the echo canceller, there is a large attenuation. Overall, by giving
It is possible to obtain an amount of echo signal cancellation that is substantially uniform with respect to frequency, and it is possible to improve the how-link margin.

Attenuators 351-35ni from the short-time power of each band signal
A second method of control is to estimate the frequency band in which howling occurs from the short-time power of each band signal, and control to increase the estimated attenuation amount of the attenuator.

One method of estimating the frequency band in which howling occurs will be explained with reference to FIG.

In FIG. 6, the horizontal axis represents frequency and the vertical axis represents short-time power level. When howling occurs, the short-term power level of each band signal has a large peak in the frequency band where howling occurs, as shown in FIG. Therefore, the short-time power level of one band and the short-time power level of the adjacent band are compared sequentially, and the threshold value at which the difference exists is determined. If it exceeds that band, it can be estimated that howling is occurring in that band.

As described above, the frequency band in which howling occurs is estimated from the short-time power of each band signal, and the attenuation amount of the attenuator for the estimated band is increased. Howling can be suppressed immediately by reducing the total gain of the band signal that is causing howling.

In addition, in the above embodiment, a rectangular window was used as the window when calculating the short-time power, but other windows may be used.
Alternatively, short-time power may be obtained by integrating with respect to time using a filter.

Effects of the Invention As described above, the present invention inserts an attenuator into the band output signal of each echo canceller of a band division type echo canceller, and calculates the short-time power of each band signal of the input signal on the transmitting side. By giving an echo signal cancellation amount that is adapted to the calculator and the previous noise level characteristics, if howling still occurs, it can be immediately suppressed, and the howling margin against environmental changes can be improved. Therefore, restrictions on usage and usage environment can be significantly relaxed, and the practical effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an echo signal canceling device in an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of the same band divider, FIG. 3 is a block diagram of the same band divider, and FIG. 4 is a block diagram of the same band divider. A block diagram of the synthesizer. Figure 5 is a characteristic diagram showing an example of temporal changes in short-term power levels of noise, voice, and voice + noise band signals. Figure 6 is a graph of each band signal when howling occurs. 7 is a configuration diagram showing a communication conference system using an echo signal canceling device, FIG. 8 is a block diagram of a conventional echo signal canceling device, and FIG. 9 is a characteristic diagram showing the short-time power level of
FIG. 10 is a block diagram of an echo canceller, and FIG. 10 is a diagram showing the ambient noise level characteristics in a room and the characteristics of the echo signal level when a conventional echo signal canceling device is used in the room. 28... Receiving side input signal terminal, 29...
- Receiving side output signal terminal, 3o... Transmitting side input signal terminal, 31...... Transmitting side output signal terminal, 32.
...First band divider, 33...Second band divider, 341-34n...Echo canceller, 351-35n...Attenuator, 36...
°゛Band synthesizer, 371 to 37n...--Short-time power calculator, 38... Attenuation amount controller. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure Kite Ball Release Figure 3 Figure 5 Time F4 Leap Figure 6 Figure 9 Liquid Figure 9 Figure 10 Station Freeze J Sho 6 Shiba, (k)/Z-n Procedure Amendment Form (Method) % Formula % [3 1 Indication of the case 1982 Patent Application No. 243848 2 Name of the invention Echo signal canceling device 3 Person making the amendment Relationship to the case Patent application Person in charge Place 1006 Bold Kadoma, Kadoma City, Osaka @ Place name
(582) Matsushita Electric Industrial Co., Ltd.
Toshihiko Yamashita 4 Agent 571 Address 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] (1) A first band divider that divides the transmitting side input signal into a plurality of frequency bands, and a second band dividing the receiving side input signal into a plurality of frequency bands having the same characteristics as the first band divider. a splitter, and a signal obtained by the first band splitter based on each band signal obtained by the first band splitter and each band signal of the same band obtained by the second band splitter. an echo canceler that cancels echo signals included in each band signal, an attenuator that attenuates each band signal from which the echo signal has been canceled by the echo canceller, and a synthesizer that synthesizes each band signal attenuated by the attenuator. a band synthesizer that generates a transmission-side output signal from which echo signals have been canceled; a short-time power calculator that calculates the short-time power of each band signal obtained by the first band divider; An echo signal canceling device comprising: an attenuation amount controller that controls an attenuation amount of the attenuator based on the short-time power of each band signal determined by a calculator. (2) The attenuation controller estimates the signal-to-noise ratio of each band signal from the short-time power of each band signal obtained by the first band divider, and attenuates the signal-to-noise ratio based on the estimated signal-to-noise ratio. 2. The echo signal canceling device according to claim 1, wherein the echo signal canceling device controls the amount of attenuation of the echo signal. (3) The attenuation controller estimates the frequency band in which howling occurs from the short-time power of each band signal obtained by the first band divider, and increases the attenuation of the attenuator in the estimated band. The echo signal canceling device according to claim 1, wherein the echo signal canceling device is controlled as follows.