JPS6154724A - Echo canceler - Google Patents

Abstract

PURPOSE:To prevent an increase in noise level by providing a means which detects and stores the background noise level in a room when there is no call made, applying a residual signal to an echo signal generating circuit through a gate circuit, and inhibiting the echo signal from being sent to the echo signal generating circuit when the residual signal falls below the background noise level. CONSTITUTION:A received signal to be radiated into a room is stored temporarily in an echo signal generating circuit 6 and processed in time series to generate and output an echo canceling signal. A signal collected by a microphone 4 is smplified by a microphone amplifier 5 and added by an adding circuit 7 to the echo canceling signal, and the sum signal is outputted from a transmission output terminal 8. Further, the output of the microphone amplifier 5 is led to a background noise detecting circuit 9 to perform constant processing during rectification, and a background noise level storage circuit 10 holds a DC voltage corresponding to the level of the background noise. The output of the adding circuit 7 is fed back to the echo signal generating circuit 6 through a gate circuit 13 as the residual signal after echo cancellation, and rectified and converted into a DC voltage by a residual signal rectifying circuit 11.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides an adaptive echo canceller that cancels echoes caused by acoustic coupling between a speaker and a microphone, which is used in a device for making calls in which a microphone and a speaker are placed in the same room. Regarding.

[Prior art]

Conventionally, in this type of echo canceller, when a received signal is input, the sound is amplified from the speaker, and the echo generation time due to the acoustic coupling ζ2 between the speaker and the microphone, that is, the direct sound and the reflected sound from the indoor wall are attenuated in the indoor space. The received signal is temporarily stored during the decay time until it becomes acceptable as an echo signal, and then time-series processing is performed using a pseudo echo cancellation function (hereinafter referred to as the cancellation function) to generate an echo cancellation signal. The echo component is removed from the transmitted signal by adding the collected sound signal from the microphone. However, the cancellation function does not become a constant function due to changes in the arrangement of speakers and microphones, movement of people in the room, changes in room temperature, etc. Therefore, in order to obtain this type of echo canceller with good performance, what is the result of adding the echo cancellation signals (hereinafter referred to as residual signal)? give feedback,
The echo cancellation function is adaptively configured to generate an echo cancellation signal that minimizes the addition result by changing the cancellation function.

[Problem that the invention seeks to solve]

However, the signal collected from the microphone naturally includes background noise in the room, and this background noise is also output as the residual signal. In the case of dogs, it does not have a large effect on the cancellation function.However, when the two components become approximately equal, the cancellation function changes due to the background noise component, and an incorrect echo cancellation signal is generated and added.

This results in an increase in the noise level.

In order to solve the above-mentioned drawbacks, the present invention provides an echo canceller configured to detect the indoor background noise level and stop the change response of the cancellation function based on this detection signal, thereby preventing the addition of noise. The objective is to improve the masking effect by focusing on the masking effect in which it is difficult to detect harmful echoes once the echo signal reaches the same level as background noise.

[Means for solving problems]

In other words, the present invention is an echo canceller used in a device for making phone calls in which a microphone and a speaker are placed in the same room, and which temporarily stores the received signal and processes it in time series in order to cancel the echo caused by the acoustic coupling between the speaker and the microphone. an echo signal generation circuit that generates an echo cancellation signal, adds the echo cancellation signal and the microphone output signal to remove an echo component, and
In an adaptive echo canceller in which the time-series processing function of the echo signal generation circuit is made variable by the residual signal, means is provided for detecting and storing an indoor background noise level when there is no call.

The residual signal is configured to be applied to the echo signal generation circuit via a gate circuit, and when the residual signal becomes equal to or lower than the background noise level.

This is an adaptive echo canceller that controls the residual signal not to be transmitted to the echo signal generation circuit.

〔Example〕

Next, an embodiment of the present invention will be described with reference to FIG.

In the embodiment of the present invention, when a reception signal is input from the reception input terminal 1, it is transmitted to the speaker amplifier 2 through the switching circuit 16. The sound is amplified into the room via the speaker 5. On the other hand, this reception signal is temporarily stored in an echo signal generation circuit 6 and subjected to time series processing 9 to generate and output an echo cancellation signal. The signal collected by the microphone 4 is amplified by a microphone amplifier 5, added to the echo cancellation signal by an adder circuit 7, and outputted from a transmission output terminal 8. Further, the output of the microphone amplifier 5 is led to a background noise detection circuit 9 where it is rectified and processed by a time constant, and a background noise level storage circuit 10 stores the background noise level (=corresponding DC voltage). The output is fed as a residual signal after echo cancellation to the echo signal generation circuit 6 via the gate circuit 16, and is rectified by the residual signal rectifier circuit 11 and converted into a DC voltage.This DC voltage is compared with the voltage held in the background noise level storage circuit 1o in the comparison/discrimination circuit 12, and when it is determined that the residual signal level is large, the gate circuit 13 is controlled to send the residual signal to the echo signal generation circuit 6. to communicate.

When the test switch 15 is operated, the switching circuit 16 is switched to the training signal generation circuit 14 side, and the memory control circuit 17 outputs data to the background noise level memory circuit 10 as if the background noise level was the minimum. Generate and apply control signals. When the test switch 15 is restored and the switching circuit 16 returns to the communication path side, the memory control circuit 17 generates a control signal as if the background noise level is at its maximum until the background noise level can be detected normally.

Furthermore, the method for detecting the background noise level will be explained in detail in 1.
Originally, it is desirable to detect background noise when there is no incoming signal or outgoing signal, that is, when both parties are not talking.

In such a communication device, the above-mentioned condition can hardly be expected. Therefore, in the present invention, the voice signal of the 0th call changes from moment to moment,
Taking advantage of the fact that background noise is usually at a constant level, the background noise detection circuit 9 uses a longer time constant for increases in level than for changes in audio level, and uses a shorter time constant for decreases in level. By configuring it so that the sound signal is removed and the background noise level is discriminated and detected. When the test switch 15 is operated, a training signal is output from the training signal generation circuit 14, amplified by the speaker 3, and input to the microphone 4. At this time, the background noise detection circuit 9 converts the training signal into a background noise signal. It was determined that there was an increase.

To be stored in the background noise level storage circuit 10 (2).

Therefore, in order to prevent the gate circuit 13 from being turned off, the memory control circuit 17 forcibly controls the background noise level to the minimum level. Moreover, test switch 15
When the background noise detection circuit 9 is restored, the actual background noise level cannot be detected due to the time constant processing of the background noise detection circuit 9. Therefore, during this period, a control signal is generated and applied as if the background noise was heavy. In this manner, the gate circuit 13 is turned off, and the time series processing function of the nine-echo echo generator circuit 6 is operated to maintain the training signal in the determined state and to break the feedback loop of the residual signal.

Note that in the present invention, the feedback system for changing the time series processing function is the gate circuit 13. As explained in the on/off section, it is also possible to implement a method in which the gain of the feedback loop is increased or decreased by using an amplifier that can control the gain in place of the gate circuit. Also included.

〔Effect of the invention〕

As explained above, the present invention prevents the deterioration of the S/N ratio by controlling the adaptability to time-series processing using means for detecting the background noise level in the room, and also makes it possible to realistically adapt to the indoor environment. This has the effect of providing an amount of echo attenuation.

[Brief explanation of drawings]

FIG. 1 shows in block diagram form an embodiment of the invention. 1...Reception input terminal, 2...Speaker amplifier, 3.
... Speaker, 4 ... Microphone, 5 ... Microphone amplifier, 6 ... Reverberation signal generation circuit, 7 ... Addition circuit. 8... Transmission output terminal, 9... Background noise detection circuit,
DESCRIPTION OF SYMBOLS 10... Background noise level memory circuit, 11... Residual signal rectification circuit, 12... Comparison discrimination circuit, 13... Gate circuit. 14... Training signal generation circuit, 15... Test switch, 16... Switching circuit, 17... Memory control circuit.

Claims (3)

[Claims] (1) A device that is used in devices that place a microphone and a speaker in the same room to make calls, and that eliminates echoes that occur due to acoustic coupling between the speaker and microphone, and that temporarily stores the received signal and processes it in time series to produce an echo. It has an echo signal generation circuit that generates a cancellation signal, adds the echo cancellation signal and the microphone output signal to remove the echo component, and varies the time series processing function of the echo signal generation circuit using the residual signal. The adaptive echo canceller includes means for detecting and storing a background noise level in a room when there is no call, and is configured to apply the residual signal to the echo signal generation circuit via a gate circuit, and The adaptive echo canceller is characterized in that the adaptive echo canceller controls to cut off the application to the echo signal generation circuit when the background noise level becomes equal to or lower than the background noise level. (2) In the echo canceller according to claim 1, the means for detecting the background noise level has a relatively long time constant for an increase in level compared to a change in audio level, and for a decrease in level, An echo canceller characterized in that it is configured to discriminately detect an audio signal and a background noise level using a short time constant. (3) The echo canceller according to claim 1, further comprising a training signal generation circuit for generating a training signal for determining an initial value of a time series processing function of the echo signal generation circuit, and generating the training signal. While the training signal is being applied as a reception signal from the circuit, the background noise level detection and storage means is forcibly stored as the minimum background noise level, and from the time when the application of the training signal is finished, the background noise level is 1. An echo canceller comprising control means for storing that the background noise level is at a maximum level until the background noise level can be detected.