Reconstruction of the music played by CSIRAC

Ron Bowlse, John Spencer and Jurij Semkiw
Ron Bowles, John Spencer and Jurij Semkiw examining the Sydney music punched paper tape for the first time.

The music played by CSIRAC was never recorded onto any audio storage format. Little was known about the music, but several people who had heard from 1951 to the mid-1960s were still around to tell of it even though it could not be heard any more. A plan was developed to reconstruct the music. Three essential people who would be needed for this endeavour, Ron Bowles, John Spencer and Jurij (George) Semkiw, were currently involved with a project at the University of Melbourne to document CSIRAC. John Spencer was a programmer on CSIRAC who remains highly skilled with CSIRAC programs and he has also written a comprehensive emulator for CSIRAC. Ron Bowles and George Semkiw were CSIRAC maintenance engineers who have intimate experience and undocumented knowledge of the internal workings of the machine.

The music was to be reconstructed as exactly as possible, to within an accuracy of better than one percent of the waveforms that would have been heard at the time the pieces were originally played. The pulse shapes, as reproduced, are well within one percent accuracy of the CSIRAC pulse shape, but the pulse timing is at least 10 times more accurate than that. This waveform accuracy would ensure a listening experience faithful to the original and would also ensure that any technical analysis of the waveform would be valid. The best reconstruction of the music was achieved by separating the reconstruction of the timing of the pulses from the reconstruction of the pulse shapes. The course of action taken was; read the program and data tapes (and get them working, a non-trivial matter), use several programs John Spencer developed from his emulator to generate the speaker pulse timing data, build hardware (some with valve technology) to reproduce the pulse shapes that appeared at the speaker terminals, combine these to reproduce the pulse stream. This pulse stream could then be played through the original speaker and recorded.


  • Audio reconstruction of CSIRAC playing Colonel Bogey (c.1951) (84KB); and
  • CSIRAC plays In Cellar Cool with a simulation of CSIRAC’s room noises(360KB) .

NOTE: QuickTime is required for playing the music.

Acknowledgements, sources and links