JPS60197025A - Echo canceller - Google Patents

Abstract

PURPOSE:To set freely a relative position of a loudspeaker and a microphone by providing a normalized amplifying attenuator, and a variable amplifying attenuator which is attenuated and amplified in a reciprocal relation to the latter attenuator. CONSTITUTION:When the maximum absolute value of an impulse response inputted to a pseudo echo path 23 becomes larger than some normal quantity by >=3dB, normalized information (c) indicates 1/2. A normalized amplifying attenuator 21 is controlled by this information (c) and attenuated by 6dB, and a variable amplifying attenuator 22 is amplified by 6dB. On the contrary, when said value goes to small by >=3dB, the normalized information (c) indicates 2, the attenuator 21 is amplified by 6dB, and the attenuator 22 is attenuated by 6dB. In such a way, both the attenuators 21, 22 are amplified and attenuated so as to go to within + or -3dB centering around some normal quantity. Accordingly, the amplification and attenuation as the whole canceller become ''0''dB. As a result, the relative position of a loudspeaker and a microphone can be set freely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an echo canceller that cancels echoes caused by acoustic coupling in remote conference systems and the like.

[Prior art]

Teleconferencing systems connect distant conference rooms using video and audio, reducing the time and costs associated with participant travel. Since this system performs two-way audio transmission, it is necessary to place a microphone and a speaker in the same room, which causes acoustic coupling. Moreover, the conference rooms are located far away.

Particularly when using a satellite link, it takes a considerable amount of time for a participant's voice to travel from the microphone through the transmission path, from the speaker in the far-end conference room to the microphone, and back again through the transmission path. A delay occurs, that is, a phenomenon in which a so-called echo can be heard.

In order to attenuate this echo, echo cancellers used in telephone lines have conventionally been used.

FIG. 1 is a block diagram showing the configuration of the above echo canceller. In the figure, transmission signal input terminal 1. Same output terminal 2. Transmission signal input terminal 3. And the inner side of the output terminal 4 is an echo can 1o, and an A/D converter 11. Input value setting circuit 12. Subtractor 33. Output value setting circuit 14. D
/A converter 15° A/D converter 16. Memory circuit 17. Pseudo-echo path 18 for emitting a pseudo-echo path signal. and a product-summer which calculates the product and sum of the output of this path 18 and the output of the storage circuit 17 and outputs a pseudo echo signal a] 9. 20 is a graphical representation of the acoustic coupling described above in the form of a circuit. This echo canceller is well known and has many parts that are the same as those described in the present invention, so a detailed explanation of its operation will be omitted. This echo canceller has a maximum of -
It is possible to cope with 6 dB of feedback, and this value of -6 dB was chosen because the echo of the telephone line is caused by an hybrid transformer. However, it is often experienced that echoes due to acoustic coupling occurring in a remote conference system have positive wraparound depending on the amplification degree of the speaker amplifier or microphone amplifier. In the conventional echo canceller shown in FIG. 1, the amount of feedback that can be processed is determined by the range of a memory (not shown) in the pseudo echo path 19. Therefore, the positions of the speaker and microphone are fixed, and the amplification degree of each amplifier is limited to the recirculated fluorescence that can be processed by the echo canceller. Therefore, the positions of the speaker and microphone are restricted, and the amplification degrees of the speaker 1 amplifier and microphone amplifier cannot be freely set.

[Purpose of the invention]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to eliminate the above-mentioned drawbacks and to free up the placement of loudspeakers and microphones.

To provide an echo canceller that allows a user to freely set the amplification degrees of a speaker amplifier and a microphone amplifier.

[Structure of the invention]

According to the present invention, there is provided a first amplification/attenuation device that amplifies and attenuates a signal to be transmitted based on normalization information, and a subtractor that calculates the difference between the output from the first amplification/attenuation device and a pseudo echo signal. a storage circuit that stores the received signal; a pseudo echo path that receives the output from the subtracter and outputs the pseudo echo path signal and the normalization information; and convolves the storage circuit and the pseudo echo path signal. , a product-summer that creates the pseudo-echo signal, and a second amplification-attenuator that attenuates and amplifies the output from the subtracter based on the normalization information in a reciprocal relationship with respect to the first amplification-attenuation device. An echo canceller having the following characteristics is obtained.

〔Example〕

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. In this figure, the same components as in FIG. 1 are given the same reference numerals.

The difference from FIG. 1 is that in place of the input/output setting circuits 12 and 14, normalization is performed which is controlled by a normalization signal C (described later) and is amplified or attenuated so as to generate an output suitable for the operation of the device. The path that is also controlled by the normalization signal C and that attenuates or amplifies the amplification or attenuation device 21 in a manner that compensates for the amplification or attenuation of the normalization amplification attenuation device 21, that is, in a reciprocal relationship, is a multiplier-summer. However, in the present invention, normalization information C determined by the range size of the internal memory is sent to the two amplification/attenuation circuits 21 and 22. with the reference numeral 23.

In this embodiment, initially the two amplification attenuators 21 and 22 are
dB. At this time, if the absolute value of the in/out response stored in the internal memory (not shown) of the pseudo echo path 23 exceeds the maximum normal value by 3 dB or more,
Each part of the in-wave response is halved and the normalization information C instructs 1/2, and under the control of this information C, the normalization amplification attenuator 21 has a variable amplification attenuation of 6 dB. Device 22 provides 6 dB amplification.

Conversely, when the maximum absolute value of the impulse response becomes 3 dB or more smaller than a certain normal value, all parts of the impulse response are doubled, and the normalization information C indicates 2.

9. The normalization amplification attenuator 21 has a 6dB amplification. The variable amplification/attenuation device 22 has an attenuation of 6 dB. From then on, each amplification attenuation device 2
1 and 22 are amplified and attenuated so that the maximum absolute value of the in-res response is within ±3 dB around a certain normal amount. Therefore, the amplification (attenuation) of the entire canceller is OdB.

〔Effect of the invention〕

As explained above, in the present invention, regardless of the amount of input from the received signal output terminal 3 to the transmitted signal input terminal 2,
Since the amount of feedback seen from the echo canceller unit 5 is made constant, there is an effect that the religions of the echo path can be determined independently of the echo canceller. Therefore, the relative positions of the speakers and microphones can be freely set within the conference room.

Further, the amplification degree of both can be freely selected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional echo canceller, and FIG. 2 is a block diagram showing an embodiment of the present invention. Explanation of symbols: 11 is an A/D converter, 13 is a subtracter. 15 is a D/A converter, 16 is an A/D converter, 17 is a storage circuit, 18 is a pseudo echo path, and 19 is a product-summer. 20 is an acoustic coupling circuit, and 21 is a normalization amplification attenuator. 22 is a variable amplification attenuator, and 23 is a pseudo echo path. a is a pseudo echo signal, b is a pseudo echo path signal. C shows each normalization information.

Claims (1)

[Scope of Claims] 1. A first amplification/attenuation device that amplifies and attenuates a signal to be transmitted using normalization information, and a subtractor that calculates the difference between the output from the first amplification/attenuation device and a pseudo echo signal. , a storage circuit that stores the received signal, and a pseudo echo path that receives an output from the subtracter and outputs a pseudo echo path signal and the normalized information. A product-summer that convolves the output of the storage circuit with the pseudo-echo path signal to create the pseudo-echo signal, and the first amplification/attenuation device that uses the normalization information to output the output from the subtracter are in a reciprocal relationship. and a second amplification attenuator that attenuates and amplifies the echo canceller. Margin below