Development of a novel subband based acoustic echo cancellation for teleconferencing

Includes bibliographical references (pages [122]-126)In teleconferencing, the use of a speaker-phone system has a troublesome problem associated with it — the acoustic echo. Traditionally, acoustic echoes have been reduced by a very high order adaptive filter to compensate for the long delay of the acoustic echo path. Such a long length adaptive filter results in a high computational complexity and slow convergence of the canceler, making it very difficult to implement in real time. Recently, multirate techniques have been introduced to overcome these difficulties by adapting several shorter filters in subbands at a reduced rate. However, the down sampling process introduces aliasing version of the original signals, especially when signals are critically decimated. A novel subband acoustic echo canceler is proposed to combat the above problems. The new canceler employs non-overlapping main filter banks with decimated auxiliary subbands to alleviate distortion due to aliasing as well as spectral gaps, while the computational simplicity is maintained. The new canceler is implemented in TMS320C30 by both SPOX and assembly language. The real-time and simulation results confirm that the new canceler is both practical and successful. The basic ideas and concepts of multirate signal processing are also included and several filter bank design techniques are discussed in this thesis.M.S. (Master of Science