A form of signal processing which enables the timbre of one signal to be modified by that of another. The original vocoder (the word is derived from ’voice coder’) was developed in 1936 at Bell Laboratories by Homer Dudley as a method for encoding, and thus reducing the bandwidth of speech signals. (The term ’bandwidth’ here signifies the amount of information either in a signal or which can be carried by a communications channel.) The classic musical application of the vocoder is to impose the formant characteristics of the voice on some other signal, perhaps from a synthesizer. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)
Bibliography: Moles, Abraham A. (1957). Machines à musique. L’apport des machines électronique et électroacoustiques à la nouvelle sensibilité musicale.