Full-duplex hands-free transparency circuit and method therefor

Abstract

A bi-directional hands-free communication device includes a microphone for transmitting a signal along a transmit path and a speaker receiving a signal transmitted along a receive path and outputting a corresponding output signal. An echo canceller, positioned in the transmit path and the receive path, cancels echo signals induced by the microphone from the speaker and outputs a corresponding cancelled signal along the transmit path, and a transparency circuit distributes state-dependent additional loss derived from the noise floor margin to the transmit path and the receive path to reduce residual echo signals output from the echo canceller. The transparency circuit measures a noise floor and inserts an artificial noise signal to the transmit path, and optionally to the receive path, at a predetermined level in relation to the measured noise floor, and dynamically adjusts the speaker to compensate for changing environmental conditions by dividing a range of an expected ambient noise power into adjacent consecutive bins, and controlling a volume of the speaker responsive to ambient noise changes only when measured noise power moves into an adjacent bin.