Paul on how Geoff Hill originally created the music:
‘Geoff Hill was not only the first software engineer, but also came from a very musical family and had perfect pitch. While working with the machine, to determine where the program was, or if it was stopped, he would have sent a few pulses to the speaker to make a noise.
‘Being musical and a programmer, he would have wondered; ‘Can I make this a steady note with any frequency?’ He would have then discovered that the pulses in memory were all at different times. So if he wanted to achieve a tone, that is an exact frequency, it would be far more difficult than producing any old note. He would have to regulate the pulse timing and send pulses regularly to the speaker.
‘I can picture him with a pencil and plenty of paper and tables of values. He would have tested multiple programs until finding one which made a steady tone. Then he would have thought, ‘Oh, that’s a bit out of tune, I’ll have to make a scale.’ Then he would have started the process of working out how to program the machine to play a scale, as in-tune as possible.’
Paul describes how CSIRAC’s music was recreated:
‘The reproduction of the music was undertaken through several steps. The music program tapes were read using a tape reader constructed to do the same job as the CSIRAC tape reader, but which put the digital information into a PC.
‘The programs were tested on a PC running the CSIRAC emulator. Electronic circuitry was built to accurately reproduce the pulse timing and shape. The timing of all of CSIRAC's instructions was documented and checked. Software was created from the emulator to read the music programs and output a file of information, about what pulses were sent to the speaker and precisely what times they were sent.
The pulse shapes were digitised then used as data in another program. This read the files of the pulse timing information and wrote a digital audio file with the appropriate pulses applied at the appropriate times. This file was then played through the speaker in the cabinet and the sound recorded to tape.’