Linear predictive coding

Linear predictive coding (LPC) is a tool used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal in compressed form, using the information of a linear predictive model.

LPC coefficient representations

LPC is frequently used for transmitting spectral envelope information, and as such it has to be tolerant for transmission errors. Transmission of the filter coefficients directly (see linear prediction for definition of coefficients) is undesirable, since they are very sensitve to errors. In other words, a very small error can distort the whole spectrum, or worse, a small error might make the precition filter unstable.

More advanced representations are such as log area rations (LAR), line sprectrum pairs (LSP) decomposition and reflection coefficients. Of these, especially LSP decomposition has gained popularity, since it ensures stability of the predictior, and spectral errors are local for small coefficient deviations.

Applications

LPC is frequently used in many applications, such as GSM telephones.