Vocoder

A vocoder is a speech analyser and synthesizer.

Originally developed as a speech coder for telecommunications applications, the vocoder has been used extensively as an electronic musical instrument.

A vocoder models the speech apparatus as an oscillator (to provide voiced sounds), a noise source (for unvoiced and plosive sounds) and a filter, modelling the vocal tract.

The filter is typically either a linear predictive filter or a sub-octave filter bank.

The analyser part detects voiced/unvoiced status, amplitude, and measures the spectrum of the signal to determine the coefficients for the synthesis filter.

The synthesizer part is an analog or digital model of the speech apparatus, as above. For musical applications, a source of musical sounds is used as the oscillator.