The VC-10 is a vocoder with a built-in microphone and a 2-1/2 octave, 32-note (F-C) keyboard. A vocoder, by definition, is a "device that continuously analyzes the frequency spectrum of on incoming signal (called the speech signal) and imparts analogous spectral characteristics to another (the carrier signal). The vocoder's output has the pitch of the carrier signal, with some or most of the timbral character and articulation of the speech signal."
[excerpted with permission from the book Vintage Synthesizers by Mark Vail, copyright Miller Freeman, Inc]
The microphone is connected via a goose-neck attachment to the vocoder and the keyboard. There is a VU meter above the keyboard so that you can tell the loudness of the "speech signal" (the signal coming from the microphone). Either you can use the built in synthesizer as your "carrier signal" or you can use the external signal inputs to input another instrument. There are controls for vibrato, depth, ensemble, and something called "accent bend".
Geoff Downes with Yes and Asia,
Steven Tyler of Aerosmith on "Prelude To Joanie" from Rock in a Hard Place,
Roger Waters of Pink Floyd,
Joe Zawinul of Weather Report
[Let us know if you have any further additions to this list.]