Yamaha Loopfactory DX200 Owner's Manual page 117

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 synthe-
sis.
Two sine wave operators (labelled "A" and "B" here) can be combined in one of two ways: horizontally 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 operator A, pro-
ducing a sound of greater harmonic complexity. This "stacking" of operators is called Frequency Modulation
(FM) synthesis.
To sum it up, when two operators are combined horizontally, both operators generate the sound; when com-
bined 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.
Appendix
FM Tone Generation
117