11
Envelopes and Amplifier
Synthesis Tutorial
An Organ sound quickly attains
full volume when a key is
pressed. It stays at full volume
until the key is released, at which
point the volume falls to zero.
A Piano quickly attains full vol-
ume when a key is pressed and
gradually falls back down to
zero after several seconds, even
if a key is held.
A String Section emulation
attains full volume graduall when
a key is pressed. It remains at
full volume until the key is
released, when gradually, the
volume falls to zero.
A = Attack time.
Adjusts the time it takes when a key is
pressed for the envelope to climb from zero to full volume. It
can be used to create a sound with a slow fade in.
D = Decay time.
Adjusts the time it takes for the envelope to
decay from full volume to the level set by the Sustain control.
S = Sustain level.
Sets the level that the envelope remains at
while the key is held down.
R = Release time
. Adjusts the time it takes when key is
released from the Sustain level to zero. It can be used to cre-
ate sounds that slowly fade away in volume.
Envelopes and Amplifier
In earlier paragraphs, it was determined how the pitch and tim-
bre of a sound is synthesized. This final part describes how the
volume is controlled. The volume throughout the duration of a
sound created by a musical instrument varies greatly according
to the type of instrument.
The diagrams show how three instruments have very different
volume characteristics. These volume intensity curves are
referred to as volume
envelopes
.
In an Analogue synthesizer, an Envelope Generator circuit is
connected to an
Amplifier,
which controls the Volume of the
sound.
The envelope generators have four controls that are used to
adjust the shape of the envelope.
When controlling Volume, these controls adjust the following
phases of the Envelope as shown in the illustration.
