COPElAND & lONG | 235
to be emitted at the loudspeaker, but the sound lasted no longer than a tick, a tiny fraction
of a second: Turing described the sound as ‘something between a tap, a click, and a thump’.^10
Executing the hoot instruction over and over again resulted in this brief sound being produced
repeatedly, on every fourth tick: tick tick tick click, tick tick tick click.^11
If the clicks are repeated often enough, then the human ear no longer hears discrete clicks
but a steady note. Turing realized that if the hoot instruction is repeated not simply over and
over again but in different patterns the ear hears different musical notes: for example, if the pat-
tern ‘tick tick tick click, tick tick tick tick, tick tick tick click, tick tick tick tick’ is repeated, then
the note of C 5 is heard. (The subscript indicates the octave in which the note occurs.) Turing
described C 5 as middle C, as musicians sometimes do, especially if playing an instrument with
a very high register; although it is more usual to refer to middle C as C 4 , an octave below C 5.^12
Repeating the different pattern ‘tick tick tick click, tick tick tick click, tick tick tick tick, tick tick
tick click, tick tick tick click, tick tick tick tick’ produces the note F 4 , and so on. It was a wonder-
ful discovery.
Turing seems not to have been particularly interested in programming the machine to play
conventional pieces of music. The different musical notes were used as indicators of the com-
puter’s internal state—one note for ‘job finished’, others for ‘error when transferring data from
the magnetic drum’, ‘digits overflowing in memory’, and so on.^13 Running one of Turing’s pro-
grams must have been a noisy business, with different musical notes and rhythms of clicks
enabling the user to ‘listen in’ (as Turing put it) to what the program was doing. He left it to
someone else, though, to program the first complete piece of music.
figure 23.2 Turing at the console of the Ferranti Mark I computer, which he called the ‘Mark II’.
Reproduced with permission of the University of Manchester School of Computer Science.