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4.12
The Sample & Hold Module (S/H)
The Sample & Hold Module produces stepped output signal levels, by sampling the instantaneous value of
any signal at its input. The stepped levels produced in this manner are useful for controlling oscillator and filter
frequencies and—occasionally—VCA gain.
The S/H circuit has a signal input (the waveform to be sampled), a trigger input, and an output giving the result of
the sampling operation. The trigger input is defaulted from the internal clock, but any square or pulse wave, or
the keyboard gate or trigger signals, will work.
Upon being triggered, the S/H sets its output level to the same value as the input signal at that instant. After the
trigger, the output signal will hold that level until the next trigger pulse.
Any signal whatsoever may be sampled. The default input is from the Noise Generator, so that the step sequence
is random. The accompanying diagrams show how, when the signal being sampled is random noise, the output
voltages are correspondingly unpredictable. An infinite variety of cyclical output patterns may be obtained, on the
other hand, by sampling a periodic waveform. Different ratios of the sampling frequencies to the frequency of the
waveform being sampled create different melodic patterns (if the output level is controlling a VCO).
The level control attenuates the input signal before it is fed to the S/H circuit. The rate control actually belongs to
the internal clock; when that is disconnected from the S/H circuit, the rate control has no effect on the operation
of the S/H circuit.
4.13
The Internal Clock /Electronic Switch
The Internal Clock is a manually controlled low-frequency square wave oscillator. It is the default trigger source for
the S/H device. It is also hardwired as the clock source for the Electronic Switch.
Under MIDI control, the Internal Clock may be synchronized to incoming MIDI Beat Clocks; see section 4.1.11.4.
The Electronic Switch has two connections on one side and one on the other, as indicated by the panel graphics.
For clarity, let’s call these three jacks A-1, A-2, and B. The switch alternates between connecting A-1 to B, and A-
2 to B. It doesn’t matter which side is the signal source and which is the destination; the switch works the same
regardless.
The switching rate is governed by the Internal Clock. This is a permanent feature of the switch.
