Moog Music Voyager Old School - Manual (Page 50)

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Voyager OS User’s Manual - Glossary
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Voyager User’s Manual - Glossary
Glossary
Here are a few key terms that cover the basics of sound generation as used in the Voyager OS synthesizer.
ADSR – Abbreviation for Attack, Decay, Sustain and Release, the four stages of an envelope control voltage .
Amplitude – The strength of a sound’s vibration measured in Decibels (dB). Amplitude corresponds to the
musical term Loudness.
Control Voltage – Control voltages (also called CVs) are used in analog synthesizers to affect changes in the
sound. In the case of pitch, pressing a key on the keyboard sends a control voltage that determines the
pitch of the oscillators. The keyboard CV is set to produce an equal tempered scale. As you play up the
keyboard, the CV is raised and the pitch increases. The pitch can also be affected by other CV sources,
like an LFO, often used to produce vibrato. Other major synthesizer components that respond to CV’s
include the fi lter (the higher the CV, the higher the fi lter cutoff frequency) and the amplifi er (the higher
the CV, the higher the gain, or volume).
Envelope – An envelope describes the contours that affect the characteristics of a sound (pitch, tone and
volume) over time. For example, when a string is plucked, its amplitude is suddenly very loud, but then
dies out gradually. This describes the Volume envelope of the sound. We observe that the initial part of
the plucked sound is very bright, but then the brightness fades away. This describes the Tonal envelope
contour. We also hear the frequency of the sound go slightly higher when the string is plucked, and then
drop slightly as the note fades. This is the pitch envelope contour. A synthesizer can create these kinds
of changes by applying electrically generated envelopes to oscillators (affecting pitch), fi lters (affecting
tone) and amplifi ers (affecting volume).
Envelope Generator – A circuit that generates an envelope signal. The envelope generator creates a time-
varying signal that can be applied to any voltage-controlled circuit. The Envelope Generators in the
Voyager have four adjustable segments: Attack, Decay, Sustain and Release, also sometimes referred to as
ADSR. The Attack, Decay and Release segments are specifi ed as time parameters, while the Sustain seg-
ment is a simply a level setting. Attack specifi es the onset time of the envelope. For example, the sound
of a plucked string starts suddenly, meaning its volume envelope has a fast attack time. Decay specifi es
how quickly the onset of the envelope fades into the sustained portion. Sustain is the level at which the
envelope sustains after the initial transient (the attack and decay portion). Finally, Release determines
how long the envelope takes to fade away. An Envelope Generator uses a trigger to start and stop the
ADSR envelope. This trigger is called a gate signal, and it’s produced whenever a key is pressed on the
keyboard. The gate signal turns on and stays on as long as a key is held down. When the key is released,
the gate signal turns off. When the gate is on, the Envelope Generator is triggered and the envelope
signal moves through the Attack and Decay segments and settles at the Sustain level as long as the gate
signal is on. When the gate goes off, the release segment of the envelope begins. A new gate signal
retriggers the Envelope Generator.