An Echo Canceler for Workstation Audio

Remote conferencing using desktop workstations is becoming commonplace. Typical audio conferencing hardware consists of a room loudspeaker (often built into the workstation) and a stand-alone microphone. Because there can be strong coupling between the loudspeaker and mike, undesirable echo signals can result. We propose to eliminate these signals using well understood echo cancellation algorithms running on a vendor-supplied, off-board DSP coprocessor. We have extended the Ptolemy code generation domain to produce suitable output for the DECaudio 56001 DSP, and have used this system to implement an LMS echo canceler. We have built a 95 tap prototype which has achieved a meager echo return loss enhancement (ERLE) of 5dB. While this level is unsatisfactory, we argue from our simulations that a 10dB design will be realizable.