248 | 23 COmPUTER mUSIC
Naturally we wanted to uncover the true sound of Turing’s computer. These ‘impossible notes’
in the recording proved to be the key to doing so: using the differences in frequency between the
impossible notes and the notes that would actually have been played, we were able to calculate
how much the recording had to be speeded up in order to reproduce the original sound of the
computer.^61 It was a beautiful moment when we first heard the true sound of Turing’s computer.
To put our findings to some practical archival use, we restored the National Sound Archive
recording: this is now part of the National Sound Archive’s collection. We increased the speed
of the recording, and we filtered out extraneous noise and also removed the effects of a trouble-
some wobble in the speed of the recording. The wobble, most likely introduced by the disc-
cutting process, was another source of frequency distortion, and even caused notes to bend
slightly through their duration.
Nobody had heard the true sound of the computer since the early Ferrantis were scrapped
more than half a century ago. A German researcher David Link attempted to re-create the sound
by programming his marvellous emulation of the Mark II.^62 But an emulation is far from being
the real thing, and without the original physical components, including of course the hooter, an
emulation cannot recapture the actual sound. But now, thanks to an improbable meeting—in
New Zealand—of the 1951 recording and modern analytical techniques, we really can listen to
Turing’s Mark II. Our restoration is available at http://www.AlanTuring.net/historic_music_restored.mp3.