Combinations Of Two Operators - Yamaha PLG150-DX Owner's Manual

Combinations of Two Operators

Although the six operators can be combined in a wide variety of ways for many different sounds, here
we'll look at the fundamental combinations of just two operators, to help you understand the basics of
FM synthesis.
Two sine wave operators (labelled "A" and "B" here) can be combined in one of two ways: horizon-
tally or vertically.
(1) Horizontal Combination
When the two operators are combined horizontally, the sounds of the two are simply mixed together.
This combining of two or more different sounds is called additive synthesis.
(2) Vertical Combination
When the two operators are combined vertically, the sound of the top operator (B) "modulates" that of
the lower operator (A). In this situation, operator B produces no sound, but alters the sound of opera-
tor A, producing a sound of greater harmonic complexity. This "stacking" of operators is called Fre-
quency Modulation (FM) synthesis.
To sum it up, when two operators are combined horizontally, both operators generate the sound; when
combined vertically, one operator changes the sound, the other produces it.
A B
Mixed sound of A and B
Operator B changes or modulates the sound
B
of A (but produces no sound itself).
Operator A produces the actual sound, as
A
modulated by B.
FM Tone Generation
7