ADAPTIVE ECHO CANCELLER FOR VOICE MESSAGING SYSTEM

摘要

An apparatus and method for echo cancellation in voice-messaging and voice-response systems, to enhance recognition of received DTMF and voice signals, comprising an efficient software echo canceller using adaptive digital filtering techniques. The voice messaging system (1, fig. 1) includes analog telephone line interface modules (24) which provide digitized voice data to a digital signal processor (DSP) chip. A transmit data line (204, fig. 3) and a receive data line (202) are each coupled to a cancel module (208) with a cancel filter and an adapt/window module (220) with an adaptive digital filter. The cancel filter causes echo cancellation on the transmit data line; the adapt/window module monitors buffered transmit data in non-real time, without directly causing cancellation to occur, and selectively transfers an adjacent window of filter coefficients to the cancel filter under control of an adaptation control (230) coupled to the adapt/window module. The control identifies a plurality of frames meeting a power criterion and passes the frames to the adaptive filter, which adapts on taps in frame segments during all available DSP real time, using a "cycle steal" feature for testing whether additional DSP processor cycles are available to use for echo cancellation.