Patent ID: 7023986

Claim:
A terminal for processing an echo, the terminal being part of a communication system, the terminal comprising: a first transducer for receiving a signal, the signal including a part due to activity of a distant user; a second transducer for emitting a second signal, the second signal including (a) a useful part due to activity of a local user, (b) a background noise part, and (c) an echo part due to coupling between said first and second transducers; an adaptive echo cancellation device adapted to (a) calculate, from the first signal received by said first transducer, an estimate of the echo part of the second signal emitted by said second transducer, and (b) subtract the estimate of the second signal emitted by said second transducer to produce an output signal from the echo cancellation device; a device for processing the residual echo at the output of said adaptive echo cancellation device, said residual echo processing device comprising: a gain controller for modifying said output signal of the echo cancellation device, said gain controller including a first analyzer for distinguishing components which make up said echo part; a second analyzer for identifying components which constitute said background part; and a calculator for determining a gain variation law, so as to reduce to the maximum possible extent the levels of said components making up said echo part without substantially affecting said useful parts; and a compensator for compensating for the effects of gain variation law on said components making up said background noise part, said compensator being arranged for (a) applying a modified gain such that the output signal is at the level of said component making up said background noise if the level of the output signal as it should be after application of said gain variation law is less than the level of a corresponding component making up said background noise part determined by said second analyzer, and (b) keeping the gain as determined by said variation law if the level of the output signal as it should be after application of said gain variation law is not less than the level of a corresponding component making un said background noise part determined by said second analyzer.