Owner`s manual

42
CHAPTER 4 -
Modular Components of the TimewARP 2600
CHAPTER 4 -
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  lter frequencies and
– occasionally –
VCA
gain.
The
S/H
circuit has a
signal
input (the waveform to be sampled), a
signal input (the waveform to be sampled), a signal
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 in nite 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
Internal Clock is a manually controlled low-frequency square-wave oscillator. It is the Internal Clock
default trigger source for the
S/H
device. It is also hardwired as the clock source for the
S/H device. It is also hardwired as the clock source for the S/H
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.