User Guide

10
Attack, measured in time, specifies the onset or transient of a sound. With Volume for instance, the
sound might start suddenly as does a plucked string sound, or fade in slowly like a bowed string
crescendo. Decay is also measured in time and specifies how quickly the onset of a sound fades
into the sustained portion. Sustain is the level at which a sound sustains after the initial transient.
Release is measured in time and determines how long a sound takes to fade away after a note
is released. These four components make up an ADSR envelope generator. An envelope control
signal has to be started and stopped. The start and stop is triggered by what is called a gate
signal. A gate signal is either on or off. When it goes on, the Envelope generator is started, when
the gate goes off, the release segment of the envelope begins. (figure 9)
Low Frequency Oscillator - Also called an LFO, this is a special type of voltage controlled oscillator
that oscillates primarily below the range of human hearing. LFOs are typically used as a source of
modulation.
For instance - an LFO with a triangle waveform at about 6 Hz modulating the pitch of a VCO
sounds like vibrato. The same LFO with a square wave will sound like a trill (figure 10). An LFO
modulating a voltage controlled amplifier will sound like a tremolo.