Importance

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Abstract

The device comprises: a circuit for picking up acoustic signals with the microphone (18); a circuit for playing back audio signals with an amplifier (30) and a loudspeaker (16); an interface circuit (20) for interfacing with a telephone network or a cell phone; and a circuit for digitally processing audio signals, which circuit includes means for reducing the acoustic echo that results from interaction of the loudspeaker with the microphone. These means comprise: an echo cancellation stage (40) with an adaptive linear filter suitable for subtracting from the signal picked up by the microphone a reference signal that is derived from the signal received at the output from the interface means; a gain control stage (42) for suppressing the residual echo, and a stage (44) for selectively reducing the background noise present in the signal received at the output from the echo suppression stage. There is also provided a stage (50) for selectively reducing the background noise present upstream in the signal received at the output from the interface means for application to the audio signal playback circuit, which stage comprises means for analyzing the time coherence of the signal and suitable for determining an a priori probability of the presence/absence of speech from respective energy levels in the spectral domain, and for using said probability to estimate a noise spectrum and to derive a de-noised estimate of the received signal.

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