via Retro Thing where you'll find the full post. It's a good one so do check it out. You'll find a free mp3 of an album created with this system.The following is a small excerpt:
"In 1981, Hungarian musician and physicist Andras Szalay visited Sinclair in Cambridge where he bought a Sinclair ZX81 kit and built a computer at home. He designed an interface called the Composer, the first part of the powerful Muzix81 system, in 1982.
The Composer was a pre-MIDI sequencer software with a dedicated hardware interface for synthesizers and drum-machines. It used control-voltage."
