Crumar Spirit - Modulation Sources; MOD X and SHAPER Y Functionality

Modulation
Modulation is a change - - typically a recurring, or repetitive change. Let's
consider the case of vibrato. Vibrato is a repetitive, smooth change above
and
below a "center" pitch . The VCO's make pitched sound; we simply
must find a source that makes smooth up-and - down voltage chang. es around
zero volts so we can control the VCO. What, not another oscill ator? Right.
An oscillator connected to the control input of a VCO. Of course we will
want this control signal generator to run very slowly - - at about 6 Hz for
vibrato speed! What we need is a "low frequency" oscillator, or LFO.
MOD X
Mod X is a source of control signals. Part of this section is our needed low
frequency oscillator - - LFO . The LFO part is represented by the triangle
and square waveforms on the MOO SOURCE switch. The frequency of t his
LFO is determined by the LFO/S + H RATE control.
When any MOO SOURCE is chosen, it is routed to t he MOO X wheel where
its size may be controlled (attenuated), and sent to the MOD X TO: switch
in the WHEEL DESTI NATIONS section. All Wheel Destinations are control
inputs . All MOD SOURCES are (controller) outputs . I n some cases (e.g.
OSCI LLATOR B). one section can be used as a sound source and/or a con-
troller.
SHAPER Y
Shaper Y is a simple envelope generator in every MODE except FREE. I n the
FREE mode Shaper Y becomes a low frequency oscillator. In either case the
symmetry or shape of the output signal is determined by the SHAPE control,
as panel graphics indicate.
ATTENUATORS
An attenuator reduces the size of a signal. It is easy to hear and understand
attenuation of an audio signal - - the sound gets quieter. As signals are
pictured traditionally, attenuation causes the height (vertical) of the signal to
be reduced . The Spirit has a number of attenuators . The most obvious are
the MASTER VOLUME control and the sliders in the AUDIO MIXER ,
which control audio levels (signal size).
The FI L TER ENVELOPE AMOUNT knob attenuates the envelope sent to
the filter control inputs, allowing more subtle (smaller) movements of the
cutoff frequency.
The MOO X and SHAPER Y wheel are attenuators that let you "play" the
site of modulation signals such as vibrato.
It is useful to know that attenuation always occurs "toward zero." That is,
signal size is attenuated toward "0" volts, whether the signal is presently a
negative
voltage or positive. This allows predictable attenuation of control
signals - - some of wh ich involve only positive voltage excursions (Loudness
Envelope); others both positive and negative excursions (Triangle position of
MOO SOURCE switch).
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