In May 2009 I was lucky enough to be invited by Rob Mullender for a look around the Oramics machine, which at the time was being stored in his workshop in Brixton. I saw it a few days before it was collected by the Science Museum, who would go on to make a lovely job of restoring it.
There are plenty of sites describing how the machine works, and so I won't go in to much detail here, but basically the machine is a fascinating early synthesiser that has audio parameters controlled and sequenced by drawing on strips of clear film. The film is wound across a horizontal bed, with the graphical elements interpreted by light sensors.
Another particularly fascinating element is the wave-generating section. A shape is drawn on a glass slide, and then placed between a cathode ray tube and some light detecting components. An oscilloscope starts its cycle on the CRT, i.e. a dot traveling along the x-axis, and the y-axis is also increased at a certain rate. The dot continues along the y-axis until the light sensor detects that it has started to clear the painted area on the slide. Once this has happened the y-axis is decreased again, resulting in the path of the oscilloscope tracing the contour of the painted area. This process happens many times a second, in the audio frequency range. The rate of the x-axis gives the frequency of the note, and the y-axis gives the shape of the wave. If you drew a triangle on the slide, you would hear a triangle wave, and so on.
This system was implemented by Graham Wrench, who used technology previously developed for displaying coastlines on radar screens. There is a fascinating Sound on Sound article about it here.
The red label says 'Beware - High voltage'. Another handwritten label says simply 'This one'.
A slide with various waveforms placed above a CRT.
What does a dinosaur wave sound like?
Rob said that the blue broom handle has a mysterious but specific function within the system...
The Oramics machine about 50 years ago.
2013 update: The Oramics machine has now been restored and is on display at the Science Museum. Great to see it returned to such beautiful condition!