Old school pitch tracking.  The Fairlight CMI Voicetracker:

I found some background on this device on the web.

“The Voicetracker can be used to “double” parts, either live or from tape. The original sound can be either enhanced with the doubling sound, or replaced completely by it. The Voicetracker can follow the original pitch exactly, or quantize it to semitone steps.

Like other Fairlight products, the Voicetracker was continually updated, so not all Voicetrackers have the same features. Within a year after its introduction, Fairlight added the capability to perform “intelligent harmonization” — up to seven note harmony in a designated scale. You can create six harmony setups and switch between them in real time. This capability allows one singer to provide the sound of an entire choir. This is particulary effective if the synthesizer is patched through a vocoder, which imposes the singer’s vocal characteristics on the synthesized sound.

Fairlight Voicetracker VT-5 connection diagram

Either microphone- or line-level sound sources can be fed into the Voicetracker. These signals are fed right back out unaltered, so that they can be sent to a mixing console. Also, an audio source can be fed into the Voicetracker’s voltage controlled amplifier.

The digital inputs and outputs include MIDI in, out, and through. The Voicetracker can send MIDI note messages, along with key velocity, pitch bend, and other controls. There are also patchable footswitch jacks and a serial port for connection to a computer.

The analog outputs (pitch, gate, envelope, brightness, and purity) run from 0 to +5V, with the pitch output at 1 volt per octave. The Voicetracker also contains a built-in synthesizer, with dual DCO and DCF, which is used primarily for practice.”

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Pretty cool

Sources:

Fairlight Voicetracker 1

Fairlight Voicetracker 2

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