Echo is the repetition of a wave due to reflection from points where the characteristics of the material through which the wave propagates changes. Acoustic echoes are due to reflection of the sound waves from walls, floors, ceilings, windows and other objects. Telephone line echoes result from impedance mismatch at the telephone exchange hybrids where the subscriber’s two-wire line is connected to a four-wire line. Echoes can also result from a feedback path set up between the speaker and the microphone in a teleconference or hearing aid system. The perceptual effects of an echo depends on the time delay between the incident and the reflected waves, the strength of the reflected waves and the number of paths through which the waves are reflected. Acoustic echo is usually reflected from a multitude of different surfaces and travels through different paths. If the time delay is not too long then the acoustic echo may be perceived as a soft reverberation, and it may even add to the artistic quality of the sound. Concert halls and church halls with desirable reverberation characteristics can enhance the quality of a musical performance. Telephone line echoes, and acoustic feedback echoes in teleconference and hearing aid systems, are undesirable and annoying and can be quite disruptive. In this chapter we study the methods of removing line echoes from telephone and data telecommunication systems, and the acoustic feedback echoes from microphone-loudspeaker systems.
Unable to display preview. Download preview PDF.
- Allen J., Berkley D., Blauret J. (1977), Multi-microphone Signal Processing Technique to Remove Room Reverberation from Speech Signals, J. Acoust. Soc. Am., Vol. 62, No. 4.Google Scholar
- Armbruster W. (1992), Wideband Acoustic Echo Canceller with Two Filter Structure, Proc. EUSIPCO-92, Vol. 3, Pages 1611–17.Google Scholar
- Flanagan J. L. et al., (1991), Autodirective Microphone systems, Acoustica Vol. 73, Pages 58–71.Google Scholar
- Gao X. Y., Snelgrove W. M. (1991), Adaptive Linearisation of a Loudspeaker, ICASSP-91 Vol. 3, Pages 3589–92.Google Scholar
- Gilloire A., Vetterli M. (1994), Adaptive Filtering in Sub-bands with Critical Sampling: Analysis, Experiments and Applications to Acoustic Echo Cancellation, IEEE. Trans. Signal Processing, Vol. 40, Pages 320–28.Google Scholar
- Hart J. E., Naylor P. A., Tanrikulu O. (1993), Polyphase Allpass IIR Structures for Subband Acoustic Echo Cancellation, EuroSpeech-93, Vol. 3, Pages 1813–16.Google Scholar
- Kellermann W. (1988), Analysis and Design of Multirate Systems for Cancellation of Acoustical Echoes, IEEE Proc. ICASSP-88, Pages 2570–73.Google Scholar
- Knappe M. E. (1992), Acoustic Echo Cancellation: Performance and Structures, M. Eng. Thesis, Carleton University, Ottawa, Canada.Google Scholar
- Martin R., Altenhoner J. (1995), Coupled Adaptive Filters for Acoustic Echo Control and Noise Reduction, IEEE Proc. ICASSP-95, Vol. 5, Pages 3043–46.Google Scholar
- Oslen H. F. (1964), Acoustical Engineering, Toronto, D. Van Nostrand Inc.Google Scholar
- Sondhi M. M., Morgan D. R. (1991), Acoustic Echo Cancellation for Stereophonic Teleconferencing, IEEE Workshop on Applications of Signal Processing to Audio And Acoustics.Google Scholar
- Sondhi M. M. (1967), An Adaptive Echo Canceller, Bell Syst. tech. J. Vol. 46, Pages 497–511.Google Scholar
- Tanrikulu O., et al. (1995), Finite-Precision Design and Implementation of All-Pass Polyphase Networks for Echo Cancellation in subbands, IEEE Proc. ICASSP-95, Vol. 5, Pages 3039–42.Google Scholar
- Zelinski R. (1988), A Microphone Array with Adaptive Post-Filtering for Noise Reduction in Reverberant Rooms, IEEE Proc. ICASSP-88, Pages 2578–81.Google Scholar