Moog-music Slim Phatty User Manual download pdf (Page 72)

Page 74

Slim Phatty User’s Manual - Glossary

Page 75

Slim Phatty 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 efcient 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 lter 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 lter 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 SP’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 amplied, 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 ute generates high

pitches.

Pole (or poles) – A term referring to the design of a lter circuit. Each lter pole adds 6 dB/Octave of

attenuation to the lter response, so while a single pole lter has a 6dB/Octave response, a 4-pole lter (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.

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Moog-music Slim Phatty User Manual Page 72