JPH0758673A - Echo preventing circuit - Google Patents

Abstract

PURPOSE:To satisfy the echo preventing amount of approximately 10dB by lowering the volume gain of signals from a microphone even when an echo preventing function is available only from an echo canceller and is insufficient. CONSTITUTION:When the voice of an opposite party is received from a line, reception signals transmitted from the line are converted to four wires by a hybrid circuit 8 and converted into digital by and A/D conversion circuit 4. Then, they are amplified by a receiving speech amplifier circuit 9 and the voice is emitted by a speaker 10. The voice is fed back from the microphone 1 and is turned to echoes. The signals including the echoes passes through a transmitting speech amplifier circuit 2 and the A/D conversion circuit 3 and pseudo echoes generated in the echo canceller 12 are subtracted by a subtractor. The signals are detected in a level detection circuit 15, a digital control circuit 17 controls a volume gain adjustment circuit 16 so as to lower the gain only when the level is equal to or less than a prescribed value, the voice of the opposite party emitted from the speaker 10 is fed back to the microphone 1 and the voice to return to the opposite party is made small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo prevention circuit having an echo canceller.

[0002]

2. Description of the Related Art In the case of a short-distance call, since the delay of the speech from the speaker's mouth and the feedback to the ear are extremely short, the echo is hardly noticed and is not a problem. However, in the case of a long-distance call, since there is a considerably large delay between the voice signal and the echo generated corresponding to the voice signal, the echo becomes troublesome and is regarded as a problem. An echo suppressor is known as a method of removing this echo.
The echo suppressor is basically a voice-operated switch, and when one of them is busy, adds an attenuation amount of 35 dB or more to the path where the echo of the 4-wire line returns. However, when both speak at the same time, the switch works so that the speaker with the stronger signal at the echo suppressor can hear the echo suppressor, so the echo suppressor is sometimes cut off or in the case of simultaneous speakers a low voice. There is a problem of separating one.

Such problems can be overcome by an echo canceller. The echo canceller uses a signal correlation technique to calculate an estimated amount of echo, generate a pseudo signal, and remove the pseudo signal from the signal on the return path. A telephone device of recent years has been developed in which the function of an echo canceller is processed by a digital signal processor, and its basic configuration will be described with reference to the block diagram of FIG. Microphone 1, transmission amplification circuit 2, first analog / digital conversion circuit 3, second analog / digital conversion circuit 4, first digital / analog circuit 5, second digital / analog circuit 6, digital signal processor 18, a hybrid circuit 8, a reception amplification circuit 9, and a speaker 10. The digital signal processor 18 includes a first echo canceller 11, a second echo canceller 12, a first subtractor 13, and a second subtractor 14.
Consists of. The transmission amplification circuit 2 amplifies a signal from the microphone 1, the analog / digital conversion circuits 3 and 4 convert an analog signal to a digital signal, and the digital / analog conversion circuits 5 and 6 are digital signals. Is converted into an analog signal, the hybrid circuit 8 performs 2-wire to 4-wire conversion, and the reception amplification circuit 9 amplifies the reception signal for outputting to a speaker. The digital signal processor 18 controls a transmission signal and a reception signal by a digital signal and has an echo prevention function. The echo cancellers 11 and 12 calculate an estimated amount of echo and send a pseudo signal, and the subtractors 13 and 14 delete one signal from the other signal.

Echo prevention when the owner transmits from the microphone 1 will be described. The transmission signal input from the microphone 1 is amplified by the transmission amplification circuit 2 and converted into digital by the first analog / digital conversion circuit 3,
The first digital / analog circuit 5 converts the original analog. The hybrid circuit 8 converts it into two lines and sends a transmission signal to the line. At this time, an echo is generated in the hybrid circuit 8. The signal including the echo is converted into analog by the second analog / digital conversion circuit 4, and the pseudo echo generated by the first echo canceller 11 is subtracted by the first subtractor 13. This prevents the transmission signal input from the microphone 1 from being echoed by the hybrid circuit 8 and emitted from the speaker 10.

Next, the prevention of echo when the voice of the other party is received from the line will be described. The reception signal transmitted from the line is converted into four lines by the hybrid circuit 8 and converted into digital by the second analog / digital conversion circuit 4. It is converted to the original analog by the second digital / analog circuit 6 via the digital signal processor 7. It is amplified by the reception amplification circuit 9 and the speaker 10 emits a voice. This voice returns from the microphone 1 and becomes an echo. The signal including the echo is transmitted to the transmission amplification circuit 2 and the first
The pseudo echo generated in the second echo canceller 12 is subtracted from the second subtractor 14 via the analog / digital conversion circuit 3 of FIG. As a result, an echo caused by the voice of the other party coming out of the speaker returning to the microphone 1 and returning to the other party is prevented.

[0006]

As the functionality of telephone devices has increased, it has been desired to improve the function (hereinafter referred to as speakerphone) of making a call from the vicinity of the receiver without the receiver. The speakerphone is more likely to generate an echo due to the voice of the other party coming out of the speaker returning to the microphone and returning to the other party, as compared with the case of carrying out a call using a general receiver. In the speakerphone, the echo canceller alone may not be able to satisfy the echo prevention amount of about 10 dB due to the functional limit of the echo canceller processed by the digital signal processor and the influence of other hardware.

[0007]

In order to solve the above problems, the present invention provides an echo prevention circuit having an echo canceller for canceling an echo generated when a voice from a speaker returns to a microphone by canceling the estimated echo. The system further comprises a level detection circuit for detecting the level of the transmission signal, a volume gain adjustment circuit for adjusting the volume of the transmission signal, and a control circuit for controlling the volume gain adjustment circuit according to the signal of the level detection circuit. When the level of the speech signal is below a predetermined value, the volume gain of the transmission signal is controlled to be lowered.

[0008]

In particular, in the speakerphone, even if the echo canceling function by the return from the speaker to the microphone is not enough with the echo canceller alone, the echo prevention amount of about 10 dB is satisfied by reducing the volume gain of the signal from the microphone. You can

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a telephone will be described with reference to the drawings. FIG. 1 is a block diagram of the present invention, and a digital signal processor is different from that of FIG. 3 of a conventional example. The digital signal processor 7 of the present invention is obtained by adding a level detection circuit 15, a sound volume gain adjustment circuit 16, and a digital control circuit 17 to a conventional digital signal processor 18. The level detection circuit 15 detects the level of the transmission signal and outputs the signal to the digital control circuit 17, and the volume gain adjustment circuit 17 adjusts the volume of the transmission signal by the input from the digital control circuit 17. The digital control 17 controls the volume gain adjusting circuit 17 based on the information of the level detecting circuit 15.

The operation when the owner transmits from the microphone 1 is the same as the above-mentioned conventional example. The case where the voice of the other party is received from the line will be described. The reception signal transmitted from the line is converted into four lines by the hybrid circuit 8 and converted into digital by the second analog / digital conversion circuit 4. It is converted to the original analog by the second digital / analog circuit 6 via the digital signal processor 7. It is amplified by the reception amplification circuit 9 and the speaker 10 emits a voice. This voice returns from the microphone 1 and becomes an echo. The signal including the echo passes through the transmission amplification circuit 2 and the first analog / digital conversion circuit 3, and the pseudo echo generated in the second echo canceller 12 is subtracted from the second subtractor 14. This signal is detected by the level detection circuit 15, and the digital control circuit 17 controls the volume gain adjustment circuit 16 so as to reduce the gain only when this level is equal to or lower than a predetermined value, and the voice of the other party from the speaker 10 is output by the microphone. The voice returned to 1 and returned to the other party is reduced. This predetermined value is set to detect the state in which the owner is making a voice. FIG. 2 is a time chart showing the timing of the volume gain of the transmission signal. The speaker output indicates whether or not the other party is making a voice, and the microphone input indicates whether or not the owner is making a voice. In the volume gain of the transmission signal, "normal" indicates a normal transmission state in which the volume gain is not reduced, and "down" indicates that the volume gain is reduced to reduce the volume heard by the other party. A is a state where only the other party is making a voice, B is a state where both are making a voice, C is a state where only the owner is making a voice, and D is a state where neither is making a voice. The volume gain control of the transmission signal is set to the normal state when the owner is making a voice B and C, and is reduced when the owner is making no voice A and D.

As described above, when the other party is making a voice, the echo canceller cancels the estimated echo from the echo of the other party's voice coming out of the speaker 10 to the microphone 1, and the gain of the volume is further increased. By lowering it, double echo prevention is performed. If the owner utters, immediately return the volume gain to normal.

[0012]

As compared with the case where a speakerphone is used to carry out a call, the speakerphone is more likely to generate an echo due to the voice of the other party coming out of the speaker returning to the microphone and returning to the other party. Even if the echo canceller is not sufficient for this echo prevention, the echo prevention amount is reduced to about 1 by reducing the volume gain of the signal from the microphone.
It becomes possible to satisfy 0 dB.

[Brief description of drawings]

FIG. 1 is a block diagram in which an embodiment of the present invention is applied to a telephone.

FIG. 2 is a time chart of the present invention.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

 1 Microphone 7 Digital Signal Processor 10 Speaker 12 Second Echo Canceller 14 Second Subtractor 15 Level Detection Circuit 16 Volume Gain Detection Circuit 17 Digital Control Circuit

Claims (1)

[Claims] 1. An echo prevention circuit having an echo canceller for preventing an echo generated when a voice from a speaker returns to a microphone by canceling an estimated echo, and a level detection circuit for detecting a level of a transmission signal, A volume gain adjusting circuit that adjusts the volume of the speech signal, and a control circuit that controls the volume gain adjusting circuit according to the signal of the level detection circuit. When the level of the transmission signal is a predetermined value or less, the transmission signal An echo prevention circuit characterized by controlling to reduce the volume gain of.