JP4292374B2 - Echo canceller - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an echo canceller apparatus that suppresses and removes echoes caused by wraparound in a communication apparatus.
[0002]
[Prior art]
In a call device, an echo canceller device is mainly used as a technique for removing echoes caused by wraparound in a hybrid circuit that performs 2-wire to 4-wire conversion and wraparound from a speaker to a microphone in a hands-free call. This echo canceller apparatus reduces the amount of sneak by estimating the signal characteristic of the sneak path with an adaptive filter and subtracting the estimated echo signal from the input signal. (For example, see Patent Document 1)
[0003]
[Patent Document 1]
JP-A-9-307484 [0004]
[Problems to be solved by the invention]
However, since the adaptive filter estimation method is based on a linearly changing signal, if the signal is cut off by a wraparound path, an echo is generated by transient operation to reduce the estimated echo signal against silence. become. That is, for example, in the trunk circuit 20 including the hybrid circuit in the case of dial transmission, the reception sound of the wraparound path is blocked to prevent the transmission sound from wrapping around. When an echo canceller device is connected to such a circuit, a transient operation that generates an echo when dialing for the above reason or a howling occurs in a hands-free communication device occurs for the above reason. In general, the control information of the dial control unit cannot be obtained in many cases, so that the operation of the echo canceller device cannot be controlled normally.
[0005]
An object of the present invention is to provide an echo canceller that can prevent transient operation and suppress the occurrence of echo even when a sneak path to which the echo canceller is connected is interrupted.
[0006]
[Means for Solving the Problems]
To achieve the above object, the echo canceller device according to the present invention is a echo canceller apparatus for reducing the echo signal that goes around the four-wire side receiver path through the echo path from the four-wire side transmission path, said An echo canceller apparatus includes: an echo canceller that generates a pseudo echo signal; an adder that reduces the echo signal by subtracting the pseudo echo signal from an input signal to the 4-wire side receiving path; and the 4-line side receiving path A silence detection unit that detects whether the input to the voice is sound or silence, and an echo canceller control unit that controls the operation of the echo canceller based on the detection result of the silence detection unit.
When the input to the 4-line receiving path is sounded, the echo canceller determines the wraparound characteristic of the echo path by estimating the adaptive filter coefficient of the adaptive filter based on the control of the echo canceller control unit. Based on this estimation, the pseudo echo signal is output, and the echo signal that has entered the 4-line side receiving path is reduced.
In addition, when the input to the 4-wire side receiving path becomes silent, the output from the 4-line side receiving path is silenced based on the control of the echo canceller control unit, and the 4-line side receiving path is set. And the echo canceller stops the estimation of the adaptive filter coefficient and maintains the adaptive filter coefficient at the estimated value immediately before the cutoff, thereby receiving the 4-line side reception. When the input to the road returns to sound, a transient operation is prevented from occurring in the estimation of the adaptive filter coefficient of the adaptive filter, and a signal due to the transient operation of the echo canceller is reduced.
Furthermore, since the echo canceller control unit includes a silence detection protection unit, the silence detection protection unit detects that the silence detection by the silence detection unit is at least twice the sampling period of the input signal to the 4-wire reception path. When it is detected that the input has continued for a long time, it is determined that the input to the 4-wire side reception path has been silenced, so that the delay time to the echo canceller (the input to the 4-wire side reception path is silent) (The time delay for transmitting the fact to the echo canceller) can be shortened (transient operation of the echo canceller can be reduced).
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of echo canceller control. In FIG. 1, 1 is a silence detection unit that detects the interruption of the input signal y (n) to the 4-wire side receiving path, and 2 is a plurality of determination results when determining the output result from the silence detection unit 1. A silence detection protection unit that outputs a detection flag dm _- flg by performing detection protection with a confirmation function such as 3 is an echo canceller control unit that controls the operation of the echo canceller based on the detection flag dm _- flg, 4 is a pseudo An echo canceller 5 that outputs an echo signal s (n) outputs, for example, a logical value “0” for outputting silence in place of the pseudo echo signal s (n) that is the output of the echo canceller 4 when the wraparound path is interrupted. 6 is a dial control unit that controls dial transmission, 7 is a dial signal transmitter, 8 is a dial mute that cuts off a wraparound path by a hybrid when dial signals are transmitted, and 9 An adder for subtracting the pseudo echo signal s (n) from the force signal y (n) and outputting the error signal ef (n), H is a hybrid circuit, 3a is the output of the silence generator 5 or the output of the adder 9. One of these switches is a 4-wire receiving path output u (n). 1 to 5 and 9 constitute an echo canceller circuit 10, and 6 to 8 and H constitute a trunk circuit 20.
[0008]
Hereinafter, with reference to the block diagram shown in FIG. 1 and the operation flow shown in FIG. 2 and FIG. 3, the details of the operation of the device of the present invention will be described using the input signal y (n) sampled at the sampling frequency of 8 kHz as an example. To do.
FIG. 2 is a flowchart for explaining the outline of the operation in the echo canceller circuit 10. In the echo canceller circuit 10, in a normal state, the reference signal x (n) from the 4-line transmission path, the input signal y (n) to the 4-line reception path, and the error signal transmitted to the 4-line reception path. Based on ef (n), the adaptive filter in the echo canceller 4 is operated at regular intervals, and the pseudo echo signal s (n) is output from the echo canceller 4.
That is, in the echo canceller circuit 10, in normal times, the error signal ef (n) obtained from the difference between the immediately preceding input signal y (n) and the immediately preceding pseudo echo signal s (n) and the 4-wire side transmission path are used. The reference signal x (n) is controlled so that the pseudo echo signal s (n) is obtained from the echo canceller 4.
Therefore, when new input data y (n) arrives (S1), subtraction between the previously calculated pseudo echo s (n) and the new input data y (n) is performed by the adder circuit 9 and new input data y (n) arrives. Error signal e (f) is obtained (S2, S3).
Next, the silence detection unit 1 performs silence detection, and the silence detection protection unit 2 performs detection protection operation (S4). Details of this will be described later with reference to FIG.
[0009]
Next, a test of "whether dial mute is detected" is performed (S5).
When the test in step S5 is “no” and there is sound, the echo canceller 4 performs adaptive calculation (S6), and the echo canceller control section 3 switches the switch 3a as shown by the solid line in FIG. (N) is the output u (n) of the 4-wire receiving path (S7), and the operation for the input data y (n) is terminated.
When the output of step S5 is “yes” and it is detected that there is no sound, the adaptive operation of the echo canceller 4 is stopped (S9), and the operation for the input data y (n) is terminated.
[0010]
The silent detection / detection protection operation in step S4 will be further described with reference to FIG.
After the start of this operation (S40), a test of "whether the previous dial mute is not detected" is performed (S41).
When this test is “yes”, the silence determination at that time is performed (S42).
When the result of this determination is “no”, the count value of the protection time measurement counter is reset (S46), and the operation of step 4 is terminated.
When the test of step S42 is “yes”, a test of “whether the detection protection time has elapsed” is performed (S43). When the test is “no”, the count value of the protection time measurement counter is incremented. (S47), the operation of step 4 is terminated. If the test in step S43 is “yes”, the count value of the protection time measurement counter is reset (S44), dial mute detection [dm ₋ flg = 1] is performed (S45), End the operation.
If the test in step S41 is “no”, the silence is determined at that time (S48), and if the determination is “yes”, the operation in step 4 is terminated.
If the result of the test in step S48 is “no”, a test of “whether the non-detection protection time has elapsed” is performed (S49). If the result of the test is “no”, the protection time measurement counter The measured value is incremented (S52), and the operation of step S4 at that time ends.
When the result of the test in step S49 is “yes”, the measurement value of the protection time measurement counter is reset (S50), and “dial mute non-detection (dm ₋ flg = 0)” is set (S51). The operation of step S4 is terminated.
[0011]
In the trunk circuit 20, when a dial signal is sent out by the dial control unit 6, the wraparound path is blocked by the dial mute 8 in synchronization therewith. At this time, the input y (n) to the 4-line receiving path of the echo canceller circuit 10 changes nonlinearly and becomes silent. The silence detection unit 1 determines silence based on the amplitude of the input signal y (n) and notifies the silence detection protection unit 2 of the silence. The silence detection protection unit 2 outputs a silence detection flag dm _- flag = 1 to the echo canceller control unit 3 after the set protection time has elapsed. In the normal state, the audio signal never crosses “0” continuously for two samples, so that the detection protection time should be 2 to 3 samples or more. In the embodiment, the echo canceller 4 from the input of the silence detector 1 is sufficient. 1 msec (8 samples) was set in consideration of the delay time until the input.
[0012]
The echo canceller control unit 3 connects the adaptive operation of the echo canceller 4 when the detection flag dm _- flag = 0 (sound), and connects the error signal ef (n) to the output u (n). On the other hand, when the detection flag dm _- flag = 1, the adaptive operation of the echo canceller 4 is stopped, and the silence generator signal is connected to u (n) to forcibly output silence.
[0013]
As described above, the adaptive operation of the echo canceller 4 is stopped and the adaptive filter coefficient before the dial mute operation is held, thereby preventing a transient operation with respect to the blocked path. After the dial signal transmission is completed and the dial mute is canceled, the state adapted to the route before the mute is maintained, so that normal echo cancellation can be immediately performed.
[0014]
In the embodiment, the maximum time required for the echo canceller 4 to stop adaptation is 1 msec at maximum, but the adaptive operation of the echo canceller 4 takes 2 to 3 seconds. On the other hand, the echo canceller 4 does not perform an unnecessary adaptive operation to generate echo or howling.
[0015]
In the present embodiment, the silence generator 5 forcibly outputs silence, but the echo canceller may be bypassed and the input signal y (n) may be output u (n).
[0016]
【The invention's effect】
As is apparent from the above, according to the present invention, silence is determined based on the amplitude of the input signal, thereby detecting the interruption of the sneak path due to dial mute when dialing, and stopping the adaptive operation of the echo canceller and the echo. By forcibly outputting silence instead of the output of the canceller, the occurrence of echo can be avoided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a flowchart showing the operation of the embodiment of FIG.
FIG. 3 is a flowchart showing the operation of the embodiment of FIG. 1;
[Explanation of symbols]
1 silence detector 2 silence detection and protection unit 3 echo canceller controller 3a switches 4 echo canceller 5 silent generator 6 dial controller 7 dial signal sender 8 dial muting 9 adder 10 echo canceller circuit 20 trunk circuits H hybrid circuit

Claims (2)

In an echo canceller that reduces echo signals that have passed from the 4-wire transmission path to the 4-wire reception path via the echo path,
The echo canceller device
An echo canceller that generates a pseudo echo signal;
An adder for reducing the echo signal by subtracting the pseudo echo signal from an input signal to the 4-wire receiving path;
A silence detector for detecting whether the input to the 4-wire side receiving path is voiced or silent;
An echo canceller control unit that controls the operation of the echo canceller based on the detection result of the silence detection unit;
When the input to the 4-wire receiving path is sound,
Based on the control of the echo canceller control unit, the echo canceller obtains the wraparound characteristic of the echo path by estimating the adaptive filter coefficient of the adaptive filter, and outputs the pseudo echo signal based on this estimation, Reduce the echo signal that wraps around the listening path,
When the input to the 4-wire receiving path is silent,
Based on the control of the echo canceller control unit, the output from the 4-wire side receiving path is silenced, the wraparound path to the output of the 4-wire side receiving path is blocked, and the echo canceller is By stopping the estimation of the adaptive filter coefficient and maintaining the adaptive filter coefficient at the estimated value immediately before the cutoff,
When the input to the 4-wire side receiving path returns to voice, a transient operation is prevented from occurring in the estimation of the adaptive filter coefficient of the adaptive filter, and a signal due to the transient operation of the echo canceller is reduced. Echo canceller device. The echo canceller control unit
It further has a silence detection protection part,
When the silence detection protection unit detects that the silence detection by the silence detection unit has continued for more than twice the sampling period of the input signal to the 4-wire receiving path,
2. The echo canceller according to claim 1, wherein it is determined that the input to the four-wire side receiving path has become silent .

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