Editing Vocoder (section)

===Linear prediction-based===
{{Further|Linear predictive coding}}

Since the late 1970s, most non-musical vocoders have been implemented using [[linear prediction]], whereby the target signal's spectral envelope (formant) is estimated by an all-pole [[Infinite impulse response|IIR]] [[digital filter|filter]]. In linear prediction coding, the all-pole filter replaces the bandpass filter bank of its predecessor and is used at the encoder to ''whiten'' the signal (i.e., flatten the spectrum) and again at the decoder to re-apply the spectral shape of the target speech signal.

One advantage of this type of filtering is that the location of the linear predictor's spectral peaks is entirely determined by the target signal, and can be as precise as allowed by the time period to be filtered. This is in contrast with vocoders realized using fixed-width filter banks, where the location of spectral peaks is constrained by the available fixed frequency bands. LP filtering also has disadvantages in that signals with a large number of constituent frequencies may exceed the number of frequencies that can be represented by the linear prediction filter. This restriction is the primary reason that LP coding is almost always used in tandem with other methods in high-compression voice coders.