Back in about 1976, US synth kit manufacturer PAiA Electronics (started by John Simonton in 1967) introduced the Model 3790 Stereo Chord Egg or ‘Encephalo-Gratification Generator’.

It used a new-fangled chip called a ‘Top Octave Generator’ which produced multiple notes at high frequencies. Those high frequency notes could then be fed into frequency-divider chips to produce multiple octaves of lower frequency notes.

The chord egg fades notes in and out while sweeping a low-pass filter across the two channels. Or it generates several notes which it fades in and out at random while sweeping a mild band pass filter across the left and right channels.

Audio: Audio samples   3790 Manual  ( Website )

In 1975 Arp introduced the 49-polyphony ARP Omni keyboard synth — ’amongst the first available polyphonic electronic keyboard synthesizers’  —  which uses a Mostek MK50240 Top Octave generator IC. For better or worse, it was their best-selling model … probably because most polyphonic synths were -really- expensive (e.g. Prophet-5, CS-80) and had limited polyphony. You could play as many notes as you had fingers and toes when using the Omni’s String and Synthesizer sections.

Today you can buy one for $100-400. (The Omni-2 is an improved model.) You might wanna hear one on Kansas tune Dust in the Wind. Or not.
▷Omni resource page▹ Omni demo 

Rumor suggests that while TOG chips aren’t made any more, there is a supply of them ‘out there’.

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