Moog Music Little Phatty Stage II - Manual (Page 73)

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LP Stage II User’s Manual - Glossary
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LP Stage II User’s Manual - Glossary
Low Frequency Oscillator – Also called an LFO, this is a special type of oscillator that generates signals
primarily below the range of human hearing (generally below 20 Hz). LFOs are typically used as a
source of modulation. For instance, an LFO with a triangle waveform, set to about 6 Hz and modulating
the pitch of a VCO results in vibrato. Changing the LFO waveform to a square wave will result in a trill.
An LFO modulating a VCA with a triangle wave creates tremolo.
LUT (Lookup Table) – A Lookup Table is a type of software data structure used to provide basic reference
information to the operating system. In the Little Phatty, LUT’s store tuning values and other
parameters used by the operating system to provide precise and efficient operation.
Mixer – A circuit for combining multiple sound sources or signals.
Modulation – Modulation is the use of a control voltage to shape a tone. Modulation has a source, a destination,
and an amount. This could be as simple as the filter cutoff of a VCF (a modulation destination) being
changed by the front panel cutoff control (the source), or as complex as mixing multiple CVs together to
modulate filter cutoff. Modulation is used in synthesis to create complex sounds and add variation.
Noise – A random audio signal having no fundamental, and where all the harmonics have equal strength (more
or less). Noise can be used as either an audio or modulation source. When used as an audio source, noise
can be used by itself to synthesize explosions or wind noises, or can be mixed with other waveforms to
create noise artifacts, such as breath sounds. When used as a modulation source, noise can introduce
instabilities to a sound, such as a ‘pitch cloud’ effect when noise modulates an oscillator. In the Little Phatty,
noise is available as a modulation source only, but external noise sources (such as from the CP-251 Control
Processor) can be applied through the LP’s Audio Input.
Oscillator – A circuit that electronically “vibrates”. When used as a sound source, an oscillator is the electronic
equivalent of a vibrating reed, or string. When amplified, an oscillator produces a pitched sound whose
frequency is determined by one or more control voltages. Changes to these voltages correspond to
changes in pitch. An oscillator’s vibration can have different shapes or waveforms, such as a triangle,
sawtooth, or square wave. The Little Phatty has two oscillators for generating sounds.
Pitch – The subjective perception of sound. A bass guitar generates low pitches, while a flute generates high
pitches.
Pole (or poles) – A term referring to the design of a filter circuit. Each filter pole adds 6 dB/Octave of
attenuation to the filter response, so while a single pole filter has a 6dB/Octave response, a 4-pole filter (like
the one in the Little Phatty) has a 24dB/Octave response.
Sample and Hold (S&H) – A circuit that generates a random control voltage at regular intervals. Traditional
sample and hold circuits employ white noise as a signal source, taking periodic samples of this signal
and holding that sample (a voltage level) until the next sample is taken. Since the signal source is noise
(a random audio signal), the output of the S&H circuit is also random. The sampling interval is typically
controlled by a low frequency oscillator (LFO). By adjusting the speed of the LFO, the speed of the S&H
circuit can be varied. In the Little Phatty, digital circuitry is used to simulate an equivalent S&H circuit, and
the LFO Rate control sets the speed. The S&H output is available as a programmable modulation source.