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Abstract

In an acoustic echo canceler of a loudspeaking telephone apparatus, a sequence of successively delayed tap signals of a remote speech signal from a transmission line are respectively weighted by filter coefficients and summed together to produce an acoustic echo replica of the speech signal. The filter coefficients are updated with a residual echo and restricted to those which correspond to an echo component of the speech signal, or peak impulse response of the acoustic feedback path between the loudspeaker and the microphone. The tap signals are also restricted to those corresponding to the restricted filter coefficients. The output of the microphone is combined in a subtractor with the acoustic echo replica, producing the residual echo. After small amplitude components of the residual echo are suppressed in a first attenuator, the output of this attenuator is supplied through a second attenuator to the line. The magnitude of the restricted tap signals of the adaptive filter is compared with the output of the first attenuator. If the former is greater than the latter, the attenuation of the second attenuator is increased. Otherwise, the attenuation of the second attenuator is decreased.

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First Claim