Yamaha SY99 Owner's Manual page 68

An algorithm is an
arrangement of six
Operators
How to change the tone
of an FM sound
In synthesizers, a device called an Envelope Generator (EG) is used to produce
a "shape in time" which can be used to control various aspects of the sound.
In Yamaha FM synthesizers, each oscillator has its own Envelope Generator
(EG) to vary its output level over time. This package of oscillator and EG is
called an Operator.
The FM tone generator of the SY99 uses six operators to produce sounds.
These six operators can be arranged in 45 different basic Algorithms (patterns
or combinations). Each operator acts either as a modulator or carrier depending
on its location in the algorithm. Only operators that appear at the bottom of an
algorithm are carriers.
For example algorithm 42 uses the six operators as three separate FM
pairs; operators 2, 4, and 6 (the modulators) are modulating operators 1, 3, and 5
(the carriers). On the other hand, algorithm 6 has only one carrier; operators 4,
5, and 6 are all modulating operator 3, which is modulating operator 2, which is
modulating operator 1.
We have learned that the output level of a modulator operator determines how
complex or bright the resulting sound will be. This means that changing the out -
put level of a modulator will affect the tone. The output of the carrier operator is
what we actually hear, so changing the output level of a carrier will affect the
volume.
Before you begin editing an FM sound, check the algorithm to see how the
operators are arranged. Notice which operators are acting as carriers and which
are acting as modulators. Then you can adjust the output levels of the various
operators to modify the tone or volume.
Each operator has its own EG to vary the operator output level over time.
Adjusting the EG of a modulator will modify how the tone will change over time.
Adjusting the EG of a carrier will modify how volume will change over time.
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