An electronic device for analysing and resynthesizing sounds. The original Vocoder (‘voice coder’) was developed by Homer Dudley in 1936 at the Bell Telephone Laboratories in Murray Hill, New Jersey, for telephonic applications; it has also proved a valuable tool in speech research and has found applications in electroacoustic music. Speech, music or other sound is analysed by a set of filters, each covering a different band of frequencies, that subdivide the entire audio spectrum; the fundamental frequency of the input is used as the ‘programme’ in a Modulation (ii) process to control the frequency of an audio oscillator (which supplies ‘buzz’) and a noise generator (‘hiss’). The resulting signal is then passed through a second set of filters, each of which is ‘tuned’ by the amount of electrical information received by their counterparts in the first set, recreating the original signal electronically. A telephone line may intervene between the analysis and synthesis sections.
About 1960 a vocoder was incorporated into the Siemens Synthesizer, which probably offered the first opportunity for musicians to use the device. Since around 1970 several manufacturers, including Bode Sound, Moog, Korg, Roland, EMS, Sennheiser, Synton, Eventide and Doepfer, have produced vocoders (some of which are controlled from a keyboard) primarily for use in electronic music studios or in live performances of rock music; the ‘harmonizer’ is a similar device. Such vocoders permit the timbre and articulation of one sound source (usually a voice) to control another. Simpler devices for producing ‘talking (or singing) instruments’, particularly in films, include the Sonovox (c1938) and, from the early 1970s, various ‘voice boxes’ (‘voice tubes’) used in rock music, which impart vocal qualities with the larynx and mouth respectively. The ‘phase vocoder’ (1966) is a software program developed at Bell, which has found a role in computer music since the late 1970s, primarily for time compression or expansion.
In 1937 Dudley and others developed the speech synthesis section of the Vocoder to produce the Voder (‘voice operation demonstrator’), a successor to the keyboard-controlled speaking machines devised from the end of the 18th century onwards. The filters are controlled by two independent five-note keyboards. The right thumb also operates a ‘quiet’ key for fricative consonants and three central ‘stops’ for plosive ones, and there is a pitch-control pedal for inflection; a left-hand wrist-bar switches between ‘buzz’ and ‘hiss’ (also combinable) to give voiced and unvoiced qualities. In 1948 researchers at Bell developed the Visible Speech machine, using Drawn sound in the form of speech ‘notation’ to control the coder section of a Vocoder.
H. Dudley: ‘Synthesizing Speech’, Bell Laboratories Record, xv (1936), 98–102
H. Dudley, R.R. Riesz and S.S.A. Watkins: ‘A Synthetic Speaker’, Journal of the Franklin Institute, ccxxvii (1939), 739–64; repr. in Speech Synthesis, ed. J.L. Flanagan and L.R. Rabiner (1973)
H. Dudley: ‘The Vocoder Remakes Speech’, Proceedings of the Institute of Radio Engineers, xxviii (1940), 1–47
J.L. Flanagan and L.R. Rabiner, eds.: Speech Synthesis (Stroudsburg, PA, 1973)
T. Rhea: ‘Harald Bode’s Frequency Shifters and Vocoders’, Contemporary Keyboard, vi/2 (1980), 86 only
C. Roads and others: The Computer Music Tutorial (Cambridge, MA, and London, 1996), 148, 444–6, 549, 566–77, 1094–9
HUGH DAVIES