The Voder was a manually driven speech synthesizer developed by Homer Dudley at Bell Telephone Laboratories. Details are described in US Patent 2,121,142 (filed 1937). The Voder was demonstrated at the 1939 World's Fair.
The voder was manually operated by trained technicians.G.6Pitch was controlled by a foot pedal, and ten fingers controlled the bandpass gains. Buzz/hiss selection was by means of a wrist bar. Three additional keys controlled transient excitation of selected filters to achieve stop-consonant sounds . ``Performing speech'' on the Voder required on the order of a year's training before intelligible speech could reliably be produced. The Voder was a versatile performing instrument having intriguing possibilities well beyond voice synthesis.
Dudley's Channel Vocoder