The Pro-One is a monophonic (one-voice) keyboard synthesizer. Its principal sound sources are two voltage-controlled oscillators (VCOs), referred to as OSC A and OSC B. OSC A, OSC B, and a white noise source can be mixed into the resonant low-pass filter (VCF). The filter modifies the voice timbre under control of its four-stage envelope generator. The filter may also serve as a sound source. This stage is followed by a voltage-controlled amplifier (VCA), which shapes the voice amplitude also under control of a four-stage envelope generator. The keyboard provides frequency control voltage (KYBD CV) for the oscillators and filter, and generates a GATE which controls the envelope generators.

In addition to this basic voice, the Pro-One has extensive modulation provisions. Three modulation sources are available: the filter envelope generator WILT ENV), OSC B, and a separate low-frequency oscillator (LFO). Each can be mixed and routed for either DIRECT or WHEEL-controlled modulation of five destinations: OSC A frequency (FREQ), OSC A pulse-width (PW), OSC B FREQ, OSC B PW, and filter frequency (FILTER).

This complement of analog synthesizer modules and the routings provided for their interconnection have been well-proven in the Pro-One's ancestors, the Prophet-5 and Prophet-10 polyphonic synthesizers. Besides allowing the synthesist to play up to five or ten notes at one time, these two instruments contain microcomputers which program all the control settings comprising a sound. The Pro-One is neither preset nor programmable: you always "patch" the precise sound you want with the knobs and switches on the control panel. But the Pro-One voice itself is identical to a single Prophet voice, so it is capable of as much range and expression.

Possessing the Prophet's sound and all standard monophonic synthesizer features, the Pro-One's own microcomputer makes possible innovations unheard of on a low-cost synthesizer; a 40-note sequencer, an arpeggiator, keyboard modes such as single- or multiple- triggering, and the unique automatic glide feature. An audio input with preamplifier and automatic GATE generator allows synthesizer processing of low-level inputs such as a microphone or electric guitar. The audio output can drive a monophonic or stereo amplifier, or stereo headphones. Of special interest to computer enthusiasts, the Pro-One readily interfaces for control by an external microcomputer.