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Abstract

A noise suppression circuit for a communications channel (10) comprises a hybrid device (11) coupled to the channel for providing a differential output signal corresponding to a received signal. A delay unit (12) delays the differential signal by a suitable amount to allow for the generation and subtraction of a noise estimate. A summing device (13) extracts a digital common mode signal from the channel, and a noise estimation unit (16) provides a common mode noise estimate signal in dependence upon a history of the common mode signal over a predetermined period of time and over a plurality of frequency bands. The common mode noise estimate signal is combined subtractively (19) with the delayed differential signal to cancel common mode noise elements of the delayed differential signal. The noise estimation unit may comprise an analysis filter bank (20) for producing a plurality of subband signals (S.sub.1 -S.sub.M), each at a different one of a plurality of different frequencies, a plurality of noise detection circuits (23.sub.1 -23.sub.M), each for processing a respective one of the plurality of subband signals to provide a component of the common mode noise estimate signal, and a synthesis filter bank (24) for processing the common mode noise signal components to provide the noise estimate signal.

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