of Microprocessors

604 MUSICAL ApPLICATIONS OF MICROPROCESSORS
ks/s sample rate), operates at a much lower clock rate, and can be easily
multiplexed. There is one serious problem that the variable sample rate
approach did not have and that is "harmonic overflow" or alias distortion
caused by generating frequencies beyond one-half the sample rate. This may
be controlled only by cutting back on stored waveform complexity when
high-frequency tones are being generated.
Multiplexed Digital Oscillator
Digital circuitry has the unique ability to be time multiplexed among
several, possibly unrelated, tasks. Although a large time-sharing computer is
the epitome of this concept, quite small amounts of very ordinary logic can
be multiplexed among several similar tasks and made to act like many copies
of itself. Probably the best way to illustrate time multiplexing is to describe a
specific example and then generalize from it. Since digital oscillators have
been under discussion, let's examine the design and implementation of a
multiplexed digital oscillator module having the following general specifications:
CLOCK
LOGIC
ACTIVITY
ACTIVE EDGES ~
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