JPH0964792A - Loud speaker information communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have excellent high speed and operation stability and high adaptive performance and to enable an acoustic control, always maintaining large acoustic echo canceling amount by inserting a low-pass filter into a transmitting signal output terminal and interrupting the high frequency component of a transmitting signal when howling is detected. SOLUTION: The device having the same constitution as an acoustic echo removing device 11 adopting a learning identifying method as an adaptive algorithm is composed of a howling detector 12, a band limit controller, a changeover switch 15 and a low-pass filter 16. When howling is detected by this howling detector 12, the band limit controller stops the successive update operation of a coefficient correction amount arithmetic circuit 7, operates the changeover switch 15, inserts the low-pass filter 16 and interrupts the high frequency component of a transmitting signal. Therefore, even if a communication line state is fallen into an unstable status, the generation of howling is suppressed without disconnecting the line and a speech state which is excellent in high speed and operation stability can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a communication line, a room sound field control device and a high quality voice communication conference device, and an acoustic echo in which a signal of a receiving path appears in a transmitting path through an acoustic echo path. The present invention relates to a loudspeaker information communication system using an acoustic echo canceller that removes components.

[0002]

2. Description of the Related Art Generally, an acoustic echo canceller is used in a long distance telephone line using a communication satellite and a submarine cable.
It can be roughly divided into one that removes reflection caused by impedance mismatch of the line-to-four-line converter and one that removes reverberation due to acoustic coupling of speaker's voice in a loudspeaker telephone such as a video conference system. It is composed of a variable coefficient filter and a subtraction circuit that generate pseudo-acoustic echo. The basic operation of the acoustic reverberation removing device will be described below.

FIG. 6 is a diagram showing the basic structure of an acoustic echo canceller. The reception signal input terminal 1 is connected to the reception signal output terminal 2, and the reception signal of the reception signal input terminal 1 is branched and supplied to the variable coefficient filter 3 to generate a pseudo acoustic echo. The transmission signal from the transmission signal input terminal 4 and the pseudo acoustic reverberation output from the variable coefficient filter 3 are input to a subtraction circuit 5, where the acoustic reverberation component in the transmission signal is removed, and the output of the subtraction circuit 5 is It is output to the transmission signal output terminal 6. The output of the transmission signal output terminal 6 and the signal of the reception signal input terminal 1 are input to the correction amount calculation circuit 7, and the filter coefficient of the variable coefficient filter 3 is corrected by the output of the coefficient correction amount calculation circuit 7. The reception signal is input to the reception signal input register 8 in the variable coefficient filter 3, and the sum of products of the reception signal of the reception signal input register 8 and the pseudo impulse response of the pseudo impulse response register 9 is obtained by the sum of products circuit 10. Sum of products circuit 10
Is output as a pseudo acoustic echo. The reception signal output terminal 2 and the transmission signal input terminal 4 are connected to a two-wire / four-wire converter for a long-distance telephone line, and to a speaker and a microphone for a loudspeaker system.

Assuming that the signal propagation characteristic of the acoustic echo path is linear and represented by an FIR type digital filter, if the impulse response h (t) and the input received signal x (t) are used, the sampling time interval is Is T, and the acoustic echo y _{k at} time kT is represented by y _k = h ^T x _k (1). However, h = [h ₁ , h ₂ , ..., H _n ] ^T (2) x = [x _K−1 , ..., x _Kn ] ^{T T} : transposition of vector
It is.

On the other hand, the estimated value of h at time kT is h
If s _k , the estimated value ys _k of y _k is given by ys _k = hs _k ^T x _k (3). In the acoustic reverberation removing device, when there is an audio signal at the receiving signal input terminal 1 and no acoustic signal exists at the transmitting signal input terminal 4 and only acoustic reverberation exists, the acoustic reverberation operation is performed as an adaptive operation state. This adaptive operation algorithm generally includes a learning identification method (Atsuhiko Noda, Jinichi Nagumo: “System Learning Identification Method”, Measurement and Control, 7, 9, pp. 597-605 (196
8)) is adopted. Successive correction of hs _k by the learning identification method is performed by _{hs k + 1 = hs k +} α (x k e k) / x k T x k (4). However, the e _k = y _k -ys _k, is 0 <α ≦ 1 (5) e k is referred to as residual acoustic echo. Such a calculation operation is performed in the coefficient correction amount calculation circuit 7. The contents of the pseudo impulse response register 9 include a variable coefficient series h.
_sk is stored. α is a coefficient updating gain for determining the sensitivity of estimation, and the closer the correction gain is to 1.0, the greater the amount of correction can be given, and high-speed acoustic reverberation can be removed. It is necessary to change and set according to the line condition. The actual situation is that the determination of the coefficient update gain α currently depends on empirical rules. The coefficient update gain α may be variably controlled according to the magnitude of the residual acoustic reverberation, or may be set according to the indoor characteristics (for example, Shoji Makino, Norio Koizumi: "Adaptive performance of the Eco-Canceller in the indoor sound field" On the improvement of ", IEICE (A), J71-A, 12, pp.2212-2214 (1988-12)).

Further, when a voice signal of a certain level or higher is present at the transmission signal input terminal 4, it is judged that a normal two-way communication state has occurred, and the sequential update operation of the coefficient correction amount calculation circuit 7 is stopped. To do. When the howling detection device 12 detects that the input / output relationship between the reception signal input terminal 1 and the transmission signal output terminal 6 is abnormal, the line gain control device 13
Thus, the line gain is added to the transmission signal output terminal 6 to reduce the probability of howling.

[0007]

The adaptive operation algorithm based on the least-squares estimation method such as the learning identification method can exert the maximum estimation performance when the input signal is white noise. However, since the signal that is actually input is a voice signal that has a bias in the spectrum, the target system cannot estimate the acoustic characteristics here, and residual acoustic echo is mixed in the transmitted signal, which improves the communication quality. In addition to the deterioration, in the worst case, the loop gain of the communication line exceeds 0 dB, and the howling probability becomes extremely high. In other words, in a real environment where a loudspeaker system is used, howling always occurs. This is because the line gain control device operates frequently, a large amount of attenuation is inserted in the communication path, the voice call is cut off, and it becomes an extremely unstable operation state, and it is not possible to provide a high quality voice information communication space. .

The present invention has been made in view of the above points, eliminates the above problems, and is excellent in high speed and operational stability.
It is an object of the present invention to provide a loudspeaker information communication system using an acoustic echo canceller that has high adaptive performance and performs acoustic control while always maintaining a large acoustic echo cancellation amount.

[0009]

SUMMARY OF THE INVENTION The present invention is to solve these problems and comprises a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, and a transmission signal output terminal. A variable coefficient digital filter having a pseudo impulse response register that receives the reception signal of the reception signal input terminal, and the sound of the reception signal input from the reception signal output terminal to the transmission signal input terminal through an acoustic echo path. An acoustic echo canceling device in which a coefficient sequence is sequentially updated by a coefficient correction amount arithmetic circuit so as to minimize a residual signal obtained by subtracting a pseudo acoustic echo generated by the variable coefficient digital filter from an echo component; In a loudspeaker information communication system including a howling detection device using the received signal input from a received signal input terminal and the residual signal as an evaluation signal, the howling When the output device detects howling, the successive update operation of the coefficient correction amount calculation circuit is stopped, a low-pass filter is inserted at the transmission signal output terminal, and high-frequency components of the transmission signal are cut off to perform howling. Provided is a loudspeaker information communication system with a reduced probability of occurrence.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the acoustic echo canceller of the present invention. As shown in FIG. 1, according to the present invention, the conventional reception signal input terminal 1, reception signal output terminal 2, variable coefficient digital filter 3, transmission signal input terminal 4, subtraction circuit 5, transmission signal output terminal 6, coefficient correction. Howling is applied to a device having the same configuration as the acoustic echo canceling device 11 that employs the learning identification method as an adaptive algorithm, which is composed of the quantity calculation circuit 7, the reception signal input register 8, the pseudo impulse response register 9, and the product-sum calculation circuit 10. The configuration is such that a detection device 12, a band limitation control device 14, a changeover switch 15, and a low-pass filter 16 are added. The receiving signal input terminal 1 and the receiving signal output terminal 2
And the transmission signal input terminal 4 and the transmission signal output terminal 6
, The variable coefficient digital filter 3 having the pseudo impulse response register 9 which receives the reception signal of the reception signal input terminal 1, and the transmission signal input terminal from the reception signal output terminal 2 through the acoustic echo path. The coefficient correction amount calculation circuit 7 is used to minimize the residual signal obtained by subtracting the pseudo-acoustic echo generated by the variable coefficient digital filter 3 from the acoustic echo component of the received voice signal input to High-quality loudspeaker information communication including an acoustic echo canceller 11 for sequentially updating the received signal, a howling detection device 12 using the received signal input from the received signal input terminal 1 and the residual signal as evaluation signals. In the system 17, when howling is detected by the howling detection device 12, the band limitation control device 14 stops the sequential update operation of the coefficient correction amount calculation circuit 7 and switches the switching. By operating the switch 15 to insert the low-pass filter 16, by cutting off high frequency components of the transmission signal, the high quality public address information communication system 17, characterized in that was extremely reduce the probability of howling occurrence. In the space where the high-quality loudspeaker information communication system 17 is used, the distance between walls such as an office is approximated to infinity, boundary conditions are not treated as open, and the distance between walls is finite and closed. Treated as a thing. The reverberation characteristic in such a space is
The direct sound between the speaker 20 and the microphone 21 and the reflected sound through each wall are mixed and created. FIG. 2 shows a configuration example of a mounting system including the high-quality loudspeaker information communication system 17, a space state in FIG. 3, and a living room in which the high-quality loudspeaker information communication system 17 shown in FIG. 4 is used. The spatial frequency transfer characteristic, which is one index of the echo characteristic, is shown. To measure the characteristics of FIG. 4, a TSP waveform (for example, Yoichi Suzuki, Futoshi Asano, Toshio Sone: "Simulation of transfer function of acoustic system (2)", Journal of Acoustical Society of Japan, Vol. 45, No. 1, p.
p.44-50 (1989) was used. The room to be measured is a general conference room. As shown in FIG. 4, the high frequency side is higher than the low frequency side. Considering this conversely, in the case of a shaped room sound field such as a conference room, the effect of not becoming a diffuse sound field on the low frequency side appears, and it can be said that the transfer characteristic is lowered. However, in a general conference room or the like, such a transfer characteristic is likely to occur, and if it remains as it is, the probability of howling occurring in a high frequency region is extremely high. Therefore, when the howling detection device 12 observes the line state and detects howling,
By inserting the low-pass filter 16 in a part of the line to cut off high-frequency components of the transmission signal, it is possible to greatly reduce the probability of howling.

[0011]

As described above, according to the present invention, the following excellent effects are expected.

(1) Even if the state of the communication line falls into an unstable state, howling can be suppressed and the call state can be maintained without disconnecting the line.

(2) Since it is not the continuous operation that interrupts the high frequency but the instantaneous operation, it is possible to normally have a conversation with a wide band voice and to realize a conversation with high quality.

(3) Since the fluctuation of the voice level is extremely low, it is possible to realize the voice communication which does not cause a feeling of strangeness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an acoustic echo canceller according to the present invention.

FIG. 2 is a block diagram showing an outline of a general voice communication system including a loudspeaker information communication system according to the present invention.

FIG. 3 is a diagram showing a loudspeaker system used to describe the present invention.

FIG. 4 is a diagram showing a spatial frequency transfer characteristic representing a sound field characteristic used for explaining the present invention.

FIG. 5 is a block diagram showing a basic configuration example of an acoustic echo canceller according to a conventional technique.

[Explanation of symbols]

 1 reception signal input terminal 2 reception signal output terminal 3 variable coefficient filter 4 transmission signal input terminal 5 subtraction circuit 6 transmission signal output terminal 7 correction amount calculation circuit 8 reception signal input register 9 pseudo impulse response register 10 sum of products calculation circuit 11 Acoustic echo canceller 12 Howling detector 13 Line gain controller 14 Band limiting controller 15 Changeover switch 16 Low-pass filter 17 High-quality loudspeaker information communication system 18 D / A conversion circuit 19 A / D conversion circuit 20 Speaker 21 Microphone

Claims (1)

[Claims] 1. A variable having a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, a transmission signal output terminal, and a pseudo impulse response register to which the reception signal of the reception signal input terminal is input. A coefficient digital filter and a pseudo acoustic echo generated by the variable coefficient digital filter are subtracted from the acoustic echo component of the reception signal input to the transmission signal input terminal from the reception signal output terminal through the acoustic echo path. An acoustic echo canceller in which a coefficient sequence is sequentially updated by a coefficient correction amount calculation circuit so as to minimize the obtained residual signal, the reception signal input from the reception signal input terminal, and the residual signal. In a loudspeaker information communication system including a howling detection device as an evaluation signal, when the howling detection device detects howling, the coefficient correction amount calculation circuit is sequentially updated. A loudspeaker information communication system characterized in that the new operation is stopped, a low-pass filter is inserted into the transmission signal output terminal, and the high frequency component of the transmission signal is cut off to reduce the probability of howling.