JPH0638589B2 - Eco-Cancer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an echo canceller that cancels an echo signal that interferes with a call in a voice communication or the like.

(Prior Art) In loud-speaking communication, the sound that is amplified by a speaker is picked up by a microphone while being repeatedly reflected in the room, so that a phenomenon occurs in which the received signal mixes with the transmitted signal after a short delay, and often the The naturalness is impaired.

For this reason, an echo canceller is conventionally inserted in the line as shown in FIG. 1 to prevent this.

FIG. 1 is an explanatory diagram of an echo canceller.

In FIG. 1, an echo signal which is an obstacle to the speaker A is generated in the speaker / microphone system on the speaker B side.

The echo canceller uses the simulated echo path 101 response signal for the received signal x (t). Are sequentially corrected using x (t) and y (t) so that they become equal to the echo signal y (t) for the received signal x (t), Is subtracted from the transmission signal z (t) consisting of the echo signal y (t) and the transmission signal n (t) of the speaker B by the subtractor 102 to eliminate the echo signal y (t) and the transmission of the speaker B. Only the talk signal n (t) is sent to the speaker A.

FIG. 2 is a block diagram of a conventional echo canceller.

This echo canceller comprises a digital filter 201, an echo path estimation circuit 202, a reception signal level detection circuit 203, a simultaneous call detection circuit 204, a transmission signal level detection circuit 205, and a subtractor 102.

Digital filter 201 has k samples A non-recursive digital filter with N coefficients
The echo path estimation circuit 202 uses the sampled x (k), z
(k) ensures that the digital filter 201 matches the echo path characteristics. Determine.

this Amendments are generally sequential The following calculation is repeated and the correction term Δ (k) is sequentially added to bring the digital filter 201 closer to the true echo path characteristic.

There are various methods for calculating Δ (k) in the equation (2).
In the method called learning identification method, a sequence of sampled received signals And residual signal obtained by subtractor 102 Due to Is calculated.

The echo path is estimated by the above circuits, and finally when n (k) = 0 Becomes

Many estimation methods, including learning identification methods, use simultaneous calls (n ≠
In case of 0) The received signal level detection circuit 20
3. A simultaneous call is detected by comparing the sending / receiving signal levels obtained by the sending signal level detecting circuit 205 with the simultaneous calling detecting circuit 204. In this case, Δ (k) = 0 is set. Is prevented from being disturbed.

In this simultaneous call detection, the level of the echo signal y (k) in the transmission signal z (k) does not exceed the level of the reception signal x (k) unless the echo path has a gain. Only the transmission signal n (k) is added, and this level ratio is reversed.

The transmission / reception signal level detection circuits 203 and 205 are the norm of T samples in a certain section. However, Detect At the same time, the simultaneous call detection circuit 204 determines that the simultaneous call is in progress, and sets Δ (k) = 0 by the control signal to stop the estimation operation.

To prevent erroneous operations due to clicks and impulsive noise, and to accurately detect simultaneous calls, the number of samples T
Must be large enough.

For this reason, a delay of T samples occurs from the occurrence of the simultaneous call to the detection, the echo path estimation operation is disturbed during this time, and the disturbance remains even after the end of the simultaneous call, and there is a big problem that the echo signal canceling ability is deteriorated. .

(Object of the Invention) The present invention has been made in view of the above problems, and an echo canceller in which the canceling ability is maintained by replacing the echo path characteristic immediately after the detection of a simultaneous call with a normal value immediately before the occurrence of a simultaneous call. The purpose is to provide.

(Structure of the Invention) The present invention is characterized in that a delay circuit and an echo path characteristic storage circuit are used to give an echo path characteristic immediately before a simultaneous call occurs to a digital filter when a simultaneous call is detected, The feature is that the disturbance of the echo path estimation from the occurrence of the simultaneous call to its detection is not carried over thereafter.

FIG. 3 is an explanatory diagram of the detection of a simultaneous call, the disturbance of the echo path, and the change in the echo cancellation amount in the present invention.

As shown in FIG. 3 (a), when a simultaneous call occurs, the third
As shown in FIG. 3B, since T samples are required to detect the transmission / reception signal level, the occurrence and termination of simultaneous communication are detected with a delay of T samples.

In T sample from occurrence of simultaneous call to detection,
Since the echo path estimation is performed using the transmission signal n (t) in which the transmission signal n (t) is added to the echo signal y (t), the disturbance of the echo path estimation as shown in FIG. 3 (c). Occurs, and Fig. 3 (d)
As described above, the amount of echo cancellation decreases.

Furthermore, when simultaneous calls are frequently repeated, disturbances in echo path estimation are accumulated, and the amount of echo cancellation is greatly reduced.

FIG. 3 (e) shows a change in the echo cancellation amount according to the present invention in comparison with the conventional method.

FIG. 4 is a diagram showing a configuration of an embodiment of the present invention, in which a T sample delay circuit 401 and an echo path characteristic storage circuit 402 are provided to always store the characteristic of the digital filter 201 before T sample, When the simultaneous call detection circuit 204 detects a simultaneous call, the coefficient of the digital filter stored in the echo path characteristic storage circuit 402 is transferred to the digital filter 201, and at the same time, the estimation operation is stopped by setting Δ (k) = 0. Let

Therefore, although the echo path characteristic of the initial T sample is disturbed, when the simultaneous call is detected, the digital filter 20
Since the coefficient of 1 is replaced with the coefficient immediately before being disturbed, the echo path characteristic after the simultaneous call detection becomes normal, and the echo canceller that maintains the canceling ability can be provided.

Note that the normal echo path estimation operation is restarted after the simultaneous call ends.

(Embodiment) FIG. 5 is a diagram showing a configuration of another embodiment of the present invention.

The digital filter 201 is a non-recursive digital filter having N coefficients, and each of the N coefficients is a data bus.
It is sent to a digital delay (delay circuit) 401 through 501.

A digital delay 401 adds a delay of T samples, and its output is sent to a memory 402 capable of storing N coefficients via a data bus 502.

When the simultaneous call detection circuit 204 detects a simultaneous call, the contents of the memory 402 are sent to the digital filter 201 through the data bus 503, and at the same time, a control signal is sent to stop the estimation operation by setting Δ (k) = 0.

Generally, the data transfer time of the data buses 501, 502, 503 is sufficiently short and can be ignored. If the data transfer time is long and cannot be ignored, the delay time of the digital delay 401 is set shorter by the time required for the data transfer, so that the coefficient can be always rewritten to a coefficient T samples before the digital filter 201. Disturbance of the echo path characteristics during the simultaneous call is limited to T samples required for the simultaneous call detection, and the echo path characteristics after the simultaneous call detection are normal.

Although the norm of T samples was used here to detect the level of the transmitted / received signal, the absolute value of the transmitted / received signal T'time average value (T ': time corresponding to T sample) and peak within T'time A method of detecting using a value may be used.

Further, although the level ratio of the transmission signal and the reception signal is used for the simultaneous call detection, the level ratio of the residual signal and the reception signal may be used.

Further, although the acoustic echo path between the speaker and the microphone is considered as the echo path, an electric echo path by a hybrid transformer may be considered.

Furthermore, although the explanation has been given as all digital processing, the reception signal level detection circuit 203, the simultaneous call detection circuit 204, and the transmission signal level detection circuit 205 may be analog circuits.

(Effects of the Invention) As described above, according to the present invention, the disturbance of the echo path characteristic at the time of the simultaneous call is limited to T samples required for the simultaneous call detection, and the echo path characteristic after the simultaneous call detection is normal. Therefore, an echo canceller that maintains the erasing ability can be provided.

Further, the amount of hardware added for the present invention can be realized by the data bus, digital delay, N-tap memory, some control functions, and the like, and the effect that it is extremely small can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a conventional echo canceller, FIG. 2 is a configuration diagram of a conventional echo canceller, and FIG. 3 is a diagram showing detection of a simultaneous call according to the present invention, disturbance of an echo path during this period, and change of echo cancellation amount. Explanatory drawing, FIG. 4 is a diagram showing a configuration of an embodiment of the present invention, and FIG. 5 is a diagram showing a configuration of another embodiment of the present invention. 101 ... Simulated echo path, 102 ... Subtractor, 103 ... Speaker, 104 ... Microphone, 201 ... Digital filter, 202 ... Echo path estimation circuit, 203 ... Received signal level detection circuit, 204 ... Simultaneous Call detection circuit, 205 ... transmission signal level detection circuit, 401 ... digital delay (delay circuit), 402 ... echo path characteristic storage circuit, 501, 502, 503 ... data bus.

Claims (1)

[Claims] 1. A reception signal and a transmission signal generated when this reception signal is added to an echo path are used to successively estimate echo path characteristics, and a simulated echo signal is generated based on the simulated echo path characteristics obtained and transmitted. An echo canceller that generates a residual signal by subtracting it from the signal, cancels the echo signal, monitors the levels of the received signal and the transmitted signal, and cancels the echo path characteristic estimation operation when a simultaneous call is detected. An echo canceller having a delay circuit and a circuit for storing the echo path characteristic, wherein when the simultaneous call is detected, the echo path characteristic immediately before the occurrence of the simultaneous call is continued from the storage circuit to rewrite the simulated echo path characteristic.