Oki Electric Industry Co., Ltd.

Hiroki Gouko

Yoshio Sakata

Hideki Kamoi

An adaptive digital filter () is adapted to generate a pseudo echo Se which is produced by imitating a noise, using part of receiving signals Si and to output it. An echo produced through an echo path () is mixed, as an echo noise, with a sending signal So and this sending signal is attenuated by a level attenuator (). The level attenuator (), in order to match the amplitude level of the echo noise of the sending signal So to that of the pseudo echo, attenuates the sending signal So and feeds it to a subtracter (). The subtracter () eliminates echo noises by subtracting the pseudo echo Se from the sending signal So. Even if the echo path is in the state of amplified system, the complete elimination of the echo can be achieved accordingly.

Echo canceller

An echo cancellor having a main tap coefficient holding section to renew a tap coefficient used to establish a pseudo transmission characteristic of an echo path and a sub tap coefficient holding section to make a copy of a tap coefficient held by the main tap coefficient holding section and to hold it. The copying is made each time an echo suppressing rate is increased. Accordingly, a tap coefficient having a high echo suppressing rate is held by the sub tap coefficient holding section. In this state, if an ambient noise such as an alarm of whistle of a vehicle is mixed, renewal operation of the main tap coefficient holding section is halted and a tap coefficient held by the sub tap coefficient holding section is used. Even in the case of a divergence of the main tap coefficient, normal operation can be maintained by the tap coefficient held by the sub tap coefficient holding section accordingly.

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Tokyo, Japan

Hiroki Gouko