Yamaha DX21 - Manual (Page 26)

Operators do not have to be connected “vertically” in a modulator-carrier re-
lationship, as shown above. The outputs of two operators can also be mixed—just
as the stops in an organ are mixed. In this case the sounds are simply added together
with no modulation effect.
ALGORITHMS
We have seen two different ways that two operators may be combined. The DX21
uses four operators, offering a lot of potential connection possibilities. These dif-
ferent configurations of operator relationships are called “algorithms”, and the DX21
offers 8 algorithm choices. These are all printed right on the DX21 panel. In the
algorithm diagrams on the panel the small boxes numbered 1 through 4 are the
operators.
HOW ALGORITHMS AFFECT THE SOUND
By changing the relative frequencies between operators in a modulator-carrier re-
lationship, you change not only the fundamental pitch of the note, but also the
frequencies present in the harmonic structure. Thus, the timbre of the voice can
be precisely controlled. In addition, since each operator has its own envelope
generator (and a sophisticated one, too!), the harmonic structure of a note can
be programmed to vary over time, just as a plucked string changes its overtones
as the note decays.
Depending on the selected algorithm, operators can be stacked vertically, connected
horizontally, or both. In the vertical arrangement, when the output of one operator
is connected to the input of another the result is modulation. By convention, the
operator at the bottom—or “output” —of a stack of operators is known as a “carrier”.
All operators in the same stack above the carrier are “modulators”. By increasing
the output level of one or more modulators feeding a carrier, the number of harmonics
in the resultant sound is increased (its “bandwidth” is increased), making it more
brilliant.
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