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11
FM Tone Generation
Although the six operators can be combined in myriad ways, here the fundamental combi-
nations that involve two operators will be explained.
Two operators can be combined in the following two ways (the two operators will be
called A and B respectively):
(1) Horizontal Combination
When the two operators are combined horizontally, the sound generated by each is mixed
with the sound from the other. The actual sound (sine wave) is produced by A and B acting
together.
Combinations of Two Operators
(2) Vertical Combination
When the two operators are combined vertically, the upper operator B works to change the
sound of the lower operator A, and a complex waveform with many overtones added to it
will be the output from operator A. In this situation, the B operator serves only to change
the sound of operator A, and does not generate the actual sound. Operator A generates the
actual sound as it undergoes changes caused by B. When the upper operator works to
change the sound of the lower operator in this way, it is called FM modulation (or simply
modulation).
When these are put together, it looks like this:
• Horizontal Combination The two operators both generate the sound.
• Vertical Combination One operator is for changing the sound of the other operator.
One operator is for making the sound.
When two operators are combined vertically in this way, they both work completely dif-
ferently.
A B
The actual sound is generated by
A and B together
B changes the sound of A (it generates no tone).
While A undergoes changes caused by B, it generates
the actual sound.
B
A
Mixed sound of A and B