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.
