The general function of all speech coding methods is to analyse the signal, remove the redundancy, and efficiently code the non - redundant parts of the signal in a perceptually acceptable manner.

Classification of speech coding schemes:

Speech coding at medium - rates and below is achieved using an analysis - synthesis process.
In the analysis stage, speech is represented by a compact set of parameters which are encoded efficiently. In the synthesis stage, these parameters are decoded and used in conjuction with a reconstruction mechanism to form speech.
Analysis can be open- loop or closed loop
Parametric representation can be speech or non - speech specific.
Non - specific coders : waveform coders
Speech specific coders: vocoders
Combination of waveform coders and vocoders: hybrid coders