SOUND SYNTHESIS
3.
SOUND
SYNTHESIS
A
synthesiser
is a set of modules or “building blocks” that
can be used together
to
create many different types of sounds.
In all synthesizers. there are three basic types of modules:
sound SOURCES, sound MODIFIERS, and sound
CONTROLLERS.
The basic sound SOURCES used in the Poiy-600 are eight
Digital Controlled Oscillators
(DCOs).
The
DCOs
produce the
actual pitches, and the selected
DC0
WAVEFORM (and selec-
lion of 2’. 4’ Harmonics etc.) has a large effect on the tonal
quality (timbre) of the sound. A NOISE source is also provided.
The sound MODIFIERS for the
Poly-800
are the Voltage Con-
trolled Amplifiers
(VCAs),
the Voltage Controlled Filter
(VCF).
and the Stereo Chorus. Sound modifiers take the basic sound
produced by the sound sources and shape or “line tune” the
sound into its final form
-
what you actually hear.
l The VCF modifies the blend of overtones (and
brightness) in the sound.
l The
VCAS
control the changes in volume ievel which
provide individual note articulation how each note
attacks, decays. etc.
l The Stereo Chorus provides extra warmth and
“thickness” for almost any sound.
The sound CONTROLLERS don’t produce or modify any
sounds directly
-
they tell the sources and
modifiers
what
to do. Controllers in the
Poly-800
include the Keyboard and
Key Assigner, advanced 6.stage Envelope Generators.
Modulation Generator, Programmer, Joystick and MIDI
interface
Without controllers, there would be no way
of coordinating
the different modules in the synthesizer to produce useful
sounds.
MIDI (Musical Instrument Digital Interface) is actually an EX-
TERNAL Controller, which allows different instruments and
equipment to be coordinated for a wide range of new
possibilities.
Each of the sources, modifiers and controllers described
above have several PARAMETERS (variable settings such as
Waveform,
Cutoff, Attack Time, etc.).
A
“Prcgram”.is
the particular collection of Parameter set-
tings that results in a specific desired sound.
On many
synthesizers.
knobs must be turned to adjust the
Parameters. and it’s hard to tell what the exact values are
-
especially when you’re editing an existing program. the most
common way
of
creating new programs.
On the
Poly-800.
each parameter and its value are express.
ed by a pair of numbers:
*
The PARAMETER NUMBER (middle two digits of the
six digit DISPLAY) identifies a particular Parameter,
which is like a single control knob on other synthesizers
(Filter Cutoff, for example, is Parameter
‘-:
/
on
the
Poly-800).
l The VALUE (righthand two digits) is like the current set-
ting of that control knob,
or
Parameter (e.g.. Filter Cutoff
can have a Value between
z
and
32
).
The eight Number Buttons (also used for Program Selec-
tion). UP and DOWN buttons and large LED Display make
it easy to adjust and DOWN button and LED Display make
it easy to adjust each program parameter precisely for the
exact desired result. T
O change any aspect of
a
programm-
ed sound, you simply:
l select a Parameter
Number
*
adjust its Value. using the UP and DOWN buttons
*
repeat above to change other Parameters. as needed
Further information is given in the section on “Creating
Sounds’:
Name of
parameter
Parameter number
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