JPS61202532A - Howling suppression device - Google Patents

Abstract

PURPOSE:To obtain a device with stable operation by combining the echo canceller erasing an echos signal adaptively and a pitch controller changing the frequency component of a signal so as to absorb the howling produced due to deterioration in the echo erasure effect. CONSTITUTION:The pitch controller 6 increase or decrease the frequency of an input signal by, e.g., 2-5%. The echo canceller 5 simulates an echo signal, subtracts it from a signal entering at transmission side input terminal 3 to exclude the echo component. Thus, the echo signal component is erased by the echo canceller 5 and as to the echo signal not erased by the pitch controller 6, a howling loop is formed to reduce the scale of the hardware of the echo canceller. Further, the howling suppressing effect is high and a stable howling suppressing device is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a howling suppression device for controlling echoes and howling in teleconference systems and the like.

2. Description of the Related Art In recent years, clear and natural voice transmission has been desired as teleconferencing systems are put into practical use.

A reverberant signal is a signal generated by a speaker that is reflected by the receiver,
This is a phenomenon in which echoes return to the speaker side due to wraparound in the acoustic system, but the echoes that have returned to the transmitter side are further sent to the receiver side, forming a loop, and when this becomes an oscillation state... ringing occurs. As described above, echoes and howling significantly deteriorate call quality and become a cause of interfering with conversation. Recently, echo cancelers 2 that eliminate this echo, pitch controllers that prevent the formation of howling loops by manipulating the frequency of signals, and the like are being put into practical use.

However, in the case of the former echo canceller, when the reverberation path is an acoustic system such as in a teleconference, the reverberation time can extend to several hundred milliseconds, making it difficult to adequately suppress howling. To do this, large-scale hardware is required. for example,
Japanese Unexamined Patent Publication No. 68-3430 discloses a device that combines an echo canceller and a voice switch to reduce the scale of the hardware. However, the unnatural feeling caused by the disconnection of the voice switch remains. Furthermore, since the echo canceller estimates the echo path based on the voice of the far-end speaker, it must detect the presence or absence of the near-end speaker and stop estimating the echo path if there is a near-end speaker. At this time, the estimated echo path may be disturbed, resulting in an increase in echoes or howling.

In addition, with the latter pitch controller, the echoes are returned even though the frequency of the echoes only changes, which deteriorates the quality of the call.

In view of the above drawbacks, the present invention combines an echo canceller and a hitch controller, uses an echo canceller to remove the main component of the echo signal, and further uses a pitch controller to absorb howling caused by deterioration of the echo cancellation effect of the echo canceller. The present invention provides a howling suppression device that operates stably.

Means for Solving the Problems To achieve this object, the howling suppression device of the present invention is comprised of an echo canceller that adaptively cancels echo signals and a pitch controller that changes the frequency component of the signal.

Effect With this configuration, the echo signal can be canceled by the echo canceller, and furthermore, in order to maintain the stability of howling suppression, the frequency of the signal can be changed by the pitch controller to prevent the formation of howling loops. This makes it possible to suppress howling in a somewhat stable manner.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.
explain.

FIG. 1 shows a block diagram of a howling suppression device according to an embodiment of the present invention. In Figure 1, 1 is a receiving side input terminal, 2 is a receiving side output terminal, 3 is a transmitting side input terminal, 4 is a transmitting side output terminal, and 5 is a loop from the receiving side output terminal 2 to the transmitting side input terminal 3. 6 is a pitch controller that changes the frequency, that is, the pitch, of the received signal coming from the receiving side input terminal 1 and outputs it.

Regarding the howling suppression device configured as above,
The operation will be explained below.

First, a far-end speaker signal enters from the receiving side input terminal 1. The pitch controller 6 inputs the input signal from 2 to 6, for example.
Increase or decrease the frequency by about %. Next, the echo canceller 6 simulates the echo signal based on the estimated echo path characteristics and this received signal. Further, the receiving side output signal is inputted from the receiving side output terminal 2 to a speaker or the like and amplified. The amplified signal is collected by a microphone and returned to the transmitting side input terminal 3 as a reverberation signal. As mentioned above, the echo canceller 6 simulates this echo signal, and subtracts it from the signal input to the transmitting side input terminal 3.
Reverberation components are removed.

As described above, according to this embodiment, the echo canceller 6 cancels the echo signal component, and the pitch controller 6 prevents the echo signal that could not be completely canceled from forming a howlin loop, so that the echo canceller's hardware The scale of the wear can be reduced, and a howling suppression device that has a high howling suppression effect and is stable can be obtained.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a howling suppression device showing a second embodiment of the present invention. In the figure, 1 is a receiving side input terminal, 2 is a receiving side output terminal, 3 is a transmitting side input terminal, 4 is a transmitting side output terminal, 6 is an echo canceller, and 6 is a pitch controller, and the above is the configuration of FIG. It is similar to 10.13 is a high-pass filter, 11 and 14 are low-pass filters that send only the low-frequency components of the signal to the echo canceller 6, and the high-frequency components are sent to the echo canceller 6.
3 and then added to the output of the echo canceller in an adder 12.16. Also, an echo canceller 6, low-pass filters 11, 14, high-pass filters 10, 13,
The adders 12 and 16 together form an echo canceller section 16.

The operation of the knock-down suppression device configured as described above will be described below. The far-end speaker's signal coming in from the receiving side input terminal 1 passes through the pitch controller 6 and enters the echo canceller section 16 as in the first embodiment. Here, as shown in FIG. 3, the signal is divided into two bands by a low-pass filter and a high-pass filter at the cutoff frequency f0.

Among these, the low frequency goes into the echo canceller 6 and is used for estimating the echo signal. After passing through the echo canceller 5, the low frequency component is added to the high frequency component in an adder 12 and output from the receiving side output terminal 2. As in the first embodiment, the signal returns to the transmitter input terminal 3 as a reverberant signal. Only the low-frequency components of this echo signal are extracted by the low-pass filter 14 and sent to the echo canceller 6. The echo canceller 6 cancels only echoes in the band below the cutoff fc.

The high-frequency component is passed through the high-pass filter 13e and i) is added to the residual signal whose echoes have been canceled by the echo canceller 5 and the adder 15. The output of the adder 15 is output from the transmitting side output terminal 4.

As described above, by arranging a low-pass filter and a high-pass filter in the echo canceller section and only reducing the band to be canceled by the echo canceller, the hardware scale of the echo canceller can be further reduced significantly. Furthermore, as shown in FIG. 4, since the main component of the audio spectrum is up to I KHz, the level of reverberation in the high frequency range is low and the reverberation is not noticeable in the low frequency range.

In addition, 1. In the second embodiment, the pitch controller is placed between the receiving side input terminal and the echo canceller, but it goes without saying that it may be placed between the echo canceller and the transmitting side output terminal.

Effects of the Invention As described above, the present invention combines an echo canceller and a pitch controller.The echo canceller cancels the main component of the echo, and the pitch controller changes the frequency of the canceled residual echo, thereby preventing the formation of howling looses. This combination allows the echo canceller to be scaled down, resulting in stable operation.
Its practical effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a howling suppression device according to a first embodiment of the present invention, FIG. 2 is a block diagram of a howling suppression device according to a second embodiment of the present invention, and FIG. 3 is a block diagram of a howling suppression device according to a second embodiment of the present invention. FIG. 4 is a frequency aa characteristic diagram of the low-pass filter and high-pass filter in the second embodiment, and FIG. 4 is a characteristic diagram showing the long-term average spectrum of speech. 6...Echo canceller, 6...Pitch control 0-7.10.13...High pass filter, 11゜14...Low pass filter, 12
．． 15...Adder. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 13 High 4r! IJ” envy ()lzl

Claims (4)

[Claims] (1) A pitch controller that changes the pitch of an input signal and outputs it, and an echo canceller unit that cancels an echo signal that wraps around from the receiving side output terminal to the transmitting side input terminal,
A howling suppression device comprising a receiving side input terminal and a transmitting side output terminal. (2) The echo canceller section includes a low-pass filter that extracts the low-frequency range of the transmitted/received input signal, a high-pass filter that extracts the high-frequency range, an echo canceller that cancels echoes in the passband of the low-pass filter, and an output of the echo canceller. 2. The howling suppression device according to claim 1, further comprising an adder that adds and synthesizes the outputs of the high-pass filter. (3) The howling suppression device according to claim 1, wherein the pitch controller is located between the receiving side input terminal and the receiving side input of the echo canceller section. (4) The howling suppression device according to claim 1, wherein the pitch controller is located between the transmitting side output and the transmitting side output terminal of the echo canceller section.