Autonomous removable handsfree device for use with portable cellular telephone, has reduction unit with reduction stage to reduce background noise in signal received at output of interfacing unit for being applied to restoring circuit

摘要

The device (14) has a digital audio signal processing circuit including a reduction unit with an echo cancellation stage (40) having a linear adaptive filter to subtract a reference signal from a signal picked up by a microphone (18). A suppression stage (42) removes a residual echo and includes a gain control unit. A selective reduction stage (44) reduces background noise in the signal received at a suppression stage output. Another reduction stage (50) reduces the noise present upstream in the signal received at an output of an interfacing unit for being applied to a restoring circuit. The linear adaptive filter is characterized using an echo cancellation algorithm e.g. affin projection algorithm.