INTRODUCTION
The WP-20 Sound Effects Synthesizer does
just what it's name implies. It creates sounds
synthetically by means of electronics. It comes
very close to imitating many real sounds and can
also create sounds that do not occur in real life.
It performs this magic through the use of an osc-
illator, bandpass filter, envelope generator, low
frequency oscillator, amplifier and a white noise
source.
The versatility of the WP-20 comes from the
fact that several of it's circuits are 'Voltage
Controlled'. The frequency of the oscillator, for
example, may be varied manually by turning one of
the oscillator control knobs on the front panel.
Turning the knob varies a voltage in the oscilla-
tor circuit, thereby changing it's frequency.
The frequency of the oscillator can also be
changed by applying a changing voltage directly to
the circuit. The higher the voltage, the higher
the resulting frequency of the oscillator. A low-
er voltage will produce a lower frequency. This
voltage is called 'Control Voltage' or 'Control
Signal'. A Control Signal of constantly changing
voltage, such as a sine wave will raise and lower
or 'Modulate' the frequency of the oscillator. If
the Control Voltage Signal frequency was slow
enough, the resulting sound would be similar to a
rising and falling police siren.
Control voltage signals can also be used to
control the Bandpass Filter and the Output Ampli-
fier. One source of control voltage is a special
oscillator called a 'Low Frequency Oscillator' or
LFO. The LFO can produce square waves, triangle
waves (somewhat similar to sine waves) and ramp
waves at a frequency range of about 1Hz to 1KHZ.
Another source of control voltage is the
'Envelope Generator' (also called Attack/Decay
Generator or A.D. Generator) . Two knobs on this
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