of Microprocessors

36 MUSICAL ApPLICATIONS OF MICROPROCESSORS
restricted set of key signatures that could be played. Another difficulty was
that the pressure of delivering continuous music to the subscribers already
signed up severely limited the amount of machine time available for practice
and further refinement.
Listeners' reactions to Teleharmonium music were interesting. The
initial reaction was quite favorable and understandably so. No one had ever
heard pure, perfectly tuned sine waves before and the sparkling clear unwavering
quality of the sound was quite a novelty. Over long periods of time,
however, the novelty was replaced by subtle irritation as the overly sweet
nature of pure sine waves became apparent. The limited harmonic mixing
technique that was later developed did little to remedy the situation, since
six harmonics are too few for the lower-pitched tones and even fewer were
provided for the higher-pitched ones due to generator limitations. A related
problem was the extremely poor loudspeakers available at the time. Bass
response was totally absent and the many sharp resonances of the metal horns
would frequently emphasize particular notes or harmonics many times over
their nominal amplitude.
For Cahill, the project was a financial disaster, its fate eventually sealed
by radio broadcasting. The basic concepts live on, however, in the Hammond
electronic organs. The "tone wheels" used in these instruments are
electric generators that perform exactly as Cahill's except that the power
output is only a few microwatts rather than many kilowatts. The needed
amplification is supplied by electronic amplifiers. Mixing, click suppression,
and harmonic amplitude control are performed by resistive networks requiring
only additional amplifier gain to overcome their losses. The eighth
harmonic, which is also on the equal-tempered scale, was added, skipping
the seventh altogether. Still, the Hammond organ has a distinctive sound not
found in any other type ofelectronic organ. Even if the reader has never heard
one live, he has probably heard a record of one--over a background music
system~
Soundtrack Art
Somewhat later, around 1930 after sound was added to motion pictures,
some work was done with drawing sound waveforms directly onto
film. Theoretically, this technique is infinitely powerful, since any conceivable
sound within the frequency range of the film equipment could be drawn.
The difficulty was in figuring out exactly what to draw and how to draw it
accurately enough to get the desired result.
The magnitude of the problem can be appreciated by considering how a
single, clear tone might be drawn. The clearness ofa tone depends to a great
degree on how accurately the waveform cycles repeat. Gradual variations
from cycle to cycle are desirable, but imperfections in a single cycle add
roughness to the tone. For even the simplest of tones, the waveform would