Editing Linear predictive coding (section)

==Overview==
LPC starts with the assumption that a speech signal is produced by a buzzer at the end of a tube (for [[Voice (phonetics)|voiced]] sounds), with occasional added hissing and popping sounds (for [[Voicelessness|voiceless]] sounds such as [[sibilant]]s and [[plosive]]s). Although apparently crude, this [[Source–filter model]] is actually a close approximation of the reality of speech production. The [[glottis]] (the space between the vocal folds) produces the buzz, which is characterized by its intensity ([[loudness]]) and [[frequency]] (pitch). The [[vocal tract]] (the throat and mouth) forms the tube, which is characterized by its resonances; these resonances give rise to [[formant]]s, or enhanced frequency bands in the sound produced. Hisses and pops are generated by the action of the tongue, lips and throat during sibilants and plosives.

LPC analyzes the speech signal by estimating the formants, removing their effects from the speech signal, and estimating the intensity and frequency of the remaining buzz. The process of removing the formants is called inverse filtering, and the remaining signal after the subtraction of the filtered modeled signal is called the residue.

The numbers which describe the intensity and frequency of the buzz, the formants, and the residue signal, can be stored or transmitted somewhere else. LPC synthesizes the speech signal by reversing the process: use the buzz parameters and the residue to create a source signal, use the formants to create a filter (which represents the tube), and run the source through the filter, resulting in speech.

Because speech signals vary with time, this process is done on short chunks of the speech signal, which are called frames; generally, 30 to 50 frames per second give an intelligible speech with good compression.