8
Synthesis Tutorial
Envelopes and Amplifier
In earlier paragraphs, it was determined how the pitch and timbre of a
sound is synthesized. This final part of the Synthesis Tutorial describes
how the volume of sound is controlled. The volume throughout the
duration of a sound created by a musical instrument often varies great-
ly according to the type of instrument.
An Organ sound quickly attains full volume when a key on the keyboard
is pressed. It stays at full volume until the key is released, at which point
the volume level falls instantly to zero.
A Piano
quickly attains
full volume 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 gradually when a key is
pressed. It remains at full volume while the key is held down, but once
the key is released, the volume level gradually falls to zero.
On an Analogue synthesizer, changes which occur throughout the
duration of a note are controlled by a section known as an Envelope
Generator. The K-Station has two Envelope Generators. The circuit of
one of these is always connected to an Amplifier, which controls the
Volume of the sound when a note is played.
Note that on the K-Station, there are no controls in a section on the
front panel which deal with the Amplifier directly. The only way to hear
and control an audio signal passing through the Amplifier is to modu-
late it by using Amp Envelope controls.
Each envelope generator has four controls which are used to adjust
the shape of the envelope. The Envelope controlling the Amplifier uses
sliders.
When controlling Volume, these controls adjust the following phases of
the Envelope as shown in the illustration.
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 while a key is held down.
S = Sustain level.
Sets the volume level that the envelope remains at while the key is
held down, after the Decay time has expired.
R = Release time.
Adjusts the time it takes when key is released from the Sustain level to
zero. It can be used to create sounds that slowly fade away in volume.
A typical synthesizer will have one or more envelopes. One envelope is
always applied to the amplifier to shape the volume of each note
played. Additional envelopes can be used to dynamically alter other
sections of the synthesizer during the lifetime of each note.
The K-Station has a second Envelope Generator which may be applied
in various interesting ways. For example, it may typically be used to
modify the filter cut off frequency or change an oscillators pitch during
the lifetime of a note.
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