JP2933035B2 - Echo canceller device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller for canceling an echo signal in a voice conference.

[0002]

2. Description of the Related Art A conventional echo canceller apparatus gradually learns a transfer function of an echo path from a received signal by an estimation algorithm such as LMS, generates a pseudo echo signal identical to the echo signal, and converts the pseudo echo signal from the transmission signal. By performing the subtraction, an echo canceling operation is realized. Here, the operations necessary for the echo canceller are an estimation operation of the transfer function coefficient of the echo path and a product-sum operation for generating a pseudo echo signal.

[0003] Further, the residual echo signal which is left unerased in the echo canceling process is suppressed by adding a loss to the residual echo signal by an additional function called an echo suppressor after the process.

[0004]

In the above-described conventional echo canceller, when a received signal is present, a large amount of high-speed calculation is required because the pseudo echo generation calculation and the echo path estimation calculation are performed in real time. .

[0005] In a voice conference using the Internet,
Since the delay time of voice transmission is extremely large, the frequency of two-way communication in a conference is generally low in many cases.

[0006] In such an application, a large amount of real-time calculation of real tom required for a normal echo canceller is not required.

An object of the present invention is to provide an echo canceller device capable of realizing a large amount of calculation required for an echo canceller even with a low-speed arithmetic unit.

[0008]

According to the present invention, there is provided an echo canceller apparatus comprising: a memory for storing a reception signal and a transmission signal; and a current reception signal or a past reception signal stored in the memory as a reception input signal of the echo canceller. A first switch for selecting a signal, a second switch for selecting a current transmission signal or a past transmission signal stored in the memory as a transmission input signal of the echo canceller, and the echo canceller And a third switch for selecting a transmission signal before echo cancellation processing or a signal after echo cancellation processing as a transmission output signal, and a transmission signal and a transmission signal in the memory when there is a reception signal and no transmission signal. A received signal is stored, and when there is no received signal, the first switch and the second switch are switched to the memory side, and the stored data is stored from the memory. It reads out the previous received signal and the past transmitted signal and causes the echo canceller to perform an echo path estimating operation. When the received signal and the transmitted signal are both in the double talk state, the first switch and the second switch Switch the current reception signal and the current transmission signal respectively, perform echo cancellation with the echo canceller, select the signal after the echo cancellation processing, and select the signal before the echo cancellation processing when not in the double talk state. And a control circuit for switching the third switching device.

According to the present invention, the echo is canceled by the echo canceller only in the double talk section, and in other sections, that is, the section operated by the echo suppressor, the transmission / reception signals are stored in the memory, and the echo path estimation operation is performed. The echo canceling operation requires a real-time operation, but the echo path estimating operation does not require a real-time high-speed operation and can be performed gradually by a relatively low-speed arithmetic unit. Thus, the amount of real-time calculation of the echo canceller can be reduced.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an echo canceller device according to an embodiment of the present invention, and FIG. 2 is a timing chart showing the operation thereof.

The echo canceler of this embodiment comprises an echo canceller 1, a memory 2, and switches 31, 32, and 33.

A voice signal uttered by the other party arrives as a received signal 4. The received signal 4 is transmitted through a loudspeaker, a microphone, or other loudspeaker to an echo signal 7.
And wrap around to the sending side. The speech signal collected by a microphone or the like becomes a transmission signal 5 to be transmitted to the other party. The memory 2 stores the received signal 4 and the transmitted signal 5.

The switch 31 selects a current received signal 4 or a past received signal 4 stored in the memory 2 as a received input signal of the echo canceller 1. The switch 32 selects a current transmission signal 5 or a past transmission signal 5 stored in the memory 2 as a transmission input signal of the echo canceller 1. The switch 33 selects a transmission signal before echo cancellation processing or a signal after echo cancellation processing as a transmission output signal of the echo canceller 1.

The control circuit 6 stores the transmission signal and the reception signal 4 in the memory 2 when there is the reception signal 4 and there is no transmission signal 5, and when the reception signal 4 does not exist, the switch 31 and the switch 32 Is switched to the memory 2 side, the past received signal 4 and the past transmitted signal 5 accumulated from the memory 2 are read, and the echo canceller 1 performs an echo path estimation operation,
When the received signal 4 and the transmitted signal 5 are both in the double talk state, the switches 31 and 32 are switched to the current received signal 4 and the current transmitted signal 5, respectively. When the signal after the erasing process is selected and the state is not the double talk state, the switch 33 is switched so as to select the signal before the echo erasing process.

Next, the operation of this embodiment will be described with reference to FIG.

The state of the utterance of the other party and the state of the utterance of the own side in the audio conference are described as voiced / silent of the reception signal 4 and the transmission signal 5. That is, the sound of the transmission signal 5 is a state in which the sender on the own side is uttering, and the sound of the reception signal 4 is a state in which the utterance signal of the other side is arriving. .

In a voice conference using the Internet, since the delay time of voice transmission is extremely large, a speaker often makes a practical one-way call in which the speaker responds after confirming the content of the utterance of the other party. . For this reason, the frequency of two-way communication is lower than in a voice conference using a communication line with a small delay.

From this, most of the communication is one-way communication, and the echo suppression processing can be compensated for by the above-described echo suppressor function that causes a loss in a transmission signal or a reception signal.

The section that cannot be compensated by the echo suppressor function is
This is a section called a double talk state where both the transmission signal 5 and the reception signal 4 exist (an echo generation section in FIG. 2).

In this embodiment, only this section is echo-eliminated by the echo canceller 1 to realize a two-way communication without interruption.

That is, in other sections, communication can be performed without any problem by the echo suppressor function. Therefore, in the section operating with the echo suppressor, the echo path estimation calculation is performed.

The control circuit 6 receives and transmits signals 4,5.
Is determined, whereby the read operation and the write operation of the memory 2 are performed. The memory write accumulates a signal whose echo path can be estimated (received signal 4
And the absence of the transmission signal 5 and only the echo signal 7 is present). In the memory read, when the echo signal 7 does not exist, the previously stored transmission signal 5 is read from the memory 2 and an echo path estimation operation is performed (a section in the reception signal indicated by the echo canceller estimation operation). In the memory write and read sections, the switches 31, 32, and 33 are switched to the contact b side.
As the transmission signal 5 transmitted to the other party, a signal processed by the external echo suppressor is transmitted.

The echo canceller 1 performs an echo path estimation calculation and a pseudo echo generation calculation by using past transmission / reception signals accumulated in the read section. In this section, since the switch 33 has not selected the echo canceling signal, real-time high-speed operation is not required, and the operation can be performed gradually by a relatively low-speed operation unit.

In the section of double talk, the switches 31, 3
2 and 33 are switched to the contact a side, and perform only the echo canceling operation (simulation echo generation operation and subtraction from the actual echo signal). Although this echo canceling operation requires real-time calculation, it is a small amount of calculation compared to the calculation amount at the time of echo path estimation calculation, and is easy to realize.

Further, if there is a margin in the speed capacity of the arithmetic unit of the echo canceller apparatus, there is no problem even if the operation of the echo path estimation calculation is performed in the section indicated by the broken line in FIG.

[0027]

As described above, according to the present invention, in a voice conference having a long voice transmission delay, the amount of real-time calculation of the echo canceller can be reduced by accumulating transmission / reception signals in a memory and performing an echo path estimation calculation. With this reduction, a personal computer can be realized as a software echo canceller without requiring special hardware.

[Brief description of the drawings]

FIG. 1 is a block diagram of an echo canceller device according to an embodiment of the present invention.

FIG. 2 is a timing chart of the embodiment of FIG.

[Explanation of symbols]

 Reference Signs List 1 echo canceler 2 memory 31, 32, 33 switch 4 reception signal 5 transmission signal 6 control circuit 7 echo signal

Claims (2)

(57) [Claims] 1. An echo canceller device used for a voice conference, comprising: a memory for storing a received signal and a transmitted signal; and a current received signal or a past received signal stored in the memory as a received input signal of the echo canceller. A first switch that performs selection, a second switch that selects a current transmission signal or a past transmission signal stored in the memory as a transmission input signal of the echo canceller, and transmission of the echo canceller. A third switch for selecting a transmission signal before the echo cancellation processing or a signal after the echo cancellation processing as an output signal; and a transmission signal and a reception signal in the memory when there is a reception signal and there is no transmission signal. When there is no received signal, the first switch and the second switch are switched to the memory side, and stored from the memory. The echo canceller performs an echo path estimating operation. When the received signal and the transmitted signal are both in the double talk state, the first switch and the second Switches the current reception signal and the current transmission signal respectively, performs echo cancellation with the echo canceller, selects the signal after the echo cancellation processing, and when not in the double talk state, the signal before the echo cancellation processing. And a control circuit for switching the third switch so as to select the echo canceller. 2. The apparatus according to claim 1, wherein the echo canceller performs the echo path estimation operation not when there is no received signal but when there is the received signal and there is no transmission signal.