3aEA3. Low cost methods for mitigating hands-free acoustics problems.

Session: Wednesday Morning, May 15

Time: 9:05

Author: Peter L. Chu
Location: PictureTel Corp., 222 Rosewood Dr., Danvers, MA 01923


Key problems in hands-free acoustics for teleconferencing are acoustic echo cancellation, reverberation, noise, varying amplitude, and restricted audio bandwidth. None of these problems can be completely solved via low-cost methods, but their nuisance can be significantly reduced. For acoustic echo cancellation, a sub-band approach has been found to work well, where the speech is divided up into many bands and echo cancellation occurs individually on each band. Reverberation in speech pickup may be significantly reduced via a simple two dipole, automatically steered array which forms a dipole pattern which may be electronically rotated a full 360 deg. Background noise from fans may be suppressed using spectral subtraction techniques. Varying amplitudes of speech may be addressed by means of a voice-activated AGC (automatic gain control), where the voice detector eliminates pumping artifacts usually found in agressive AGC schemes. Finally the use of 7-kHz digital audio compression schemes alleviates the problems of muffled sounding speech due to the 3.4-kHz restricted audio bandwidth found on telephones.

from ASA 131st Meeting, Indianapolis, May 1996