hiiii dis is vishva......i wanna know more bout speech coding.....

Speech coding

Speech coding is the application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream.
The two most important applications of speech coding are mobile telephony and Voice over IP.
The techniques used in speech coding are similar to that in audio data compression and audio coding where knowledge in psychoacoustics is used to transmit only data that is relevant to the human auditory system.

Speech coding techniques can be broadly divided into two classes:
waveform coding that aims at reproducing the speech waveform as faithfully as possible and vocoders that preserve only the spectral properties of speech in the encoded signal. The waveform coders are able to produce high-quality speech at high enough bit rates; vocoders produce intelligible speech at much lower bit rates, but the level of speech quality---in terms of its naturalness and uniformity for different speakers---is also much lower.

References:
http://cslu.cse.ogi.edu/HLTsurvey/ch10node4.html
http://en.wikipediawiki/Speech_coding