CSIRAC on display. Photo courtesy of John O'Neill, via Wikipedia Commons.

A mid-20th-century computer, generally believed to be the first digital computer in the world to produce electronic music. The computer, originally dubbed the CSIR Mark I, was designed and built by the Australian government organization then known as the Council on Scientific and Industrial Research, which was renamed the Commonwealth Scientific and Industrial Research Organization (CSIRO) during the computer's construction. The CSIR Mark I was the first electronic digital computer to be built in Australia, and one of the first anywhere in the world. It was constructed using vacuum tubes (valves), and it ran its first program in 1949.

Geoff Hill, one of CSIRAC's first programmers, was an amateur musician. One of the diagnostic tools CSIRAC had was a loudspeaker that was driven directly by binary pulses from one of the computer's serial data busses. A series of 20-bit data words could be sent to this bus, and the positive and negative pulses would cause the loudspeaker's diaphragm to move. (The computer did not have a D/A converter.) At a 1000-Hz instruction cycle, these data words clocked the loudspeaker at a 20 kHz rate; by varying the contents of the data, it was possible to generate a number of pulse-type waveforms at various subjective pitches. Hill began to program the computer so the loudspeaker would output crude-sounding but recognizable melodies. This was first publicly demonstrated in 1951, and Hill was able to program a variety of popular tunes to be played by the computer.

CSIRO transferred the computer to the University of Melbourne in 1955, where it received the moniker "Commonwealth Scientific and Industrial Research Automatic Computer", or CSIRAC. A group led by Sir Thomas Cherry expanded on the techniques Hill had pioneered, and created a sort of music programming language that allowed a non-computer-trained person to program basic melodies without having to do any of the hardware-level coding, somewhat like Max Mathews' MUSIC. Unfortunately, the machine's capabilities were always hamstrung by the audio output being driven directly from the data bus, which limited the available timbres and caused unpleasant aliasing when certain frequencies clashed with the 20 kHz clock frequency. Still, a rather extensive library of music was created. However, rapid improvement in computer designs had made CSIRAC obsolete by the early 1960s, and it was shut down for the final time in 1964. Unfortunately, no original recordings of CSIRAC playing music are known to have survived.

In the 2000s, a group consisting of former CSIRAC engineers Ron Bowles, John Spencer and Jurij (George) Semkiw, set about building a machine to re-create CSIRAC music by reading the original program paper tapes. Here is a reconstructed sample of CSIRAC music. The CSIRAC itself still exists (in non-running condition), and is on display at the Scienceworks museum in Melbourne.

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