Yamaha SY99 Owner's Manual page 84

The EGs of carrier operators determine how the volume will change over time,
and the EGs of modulator operators determine how the tone will change over
time. To see which operators are acting as carriers, press F8 (Alg) to get a
graphic display of the algorithm. The operators in the bottom row are acting as
carriers.
In the algorithm used by this AFM element, operators 1 and 4 are the carriers.
Press EXIT to return to the AFM operator EG display.
Move the cursor to R1 (rate 1) of the carrier operator(s), and decrease me
value while playing. Notice that as R1 decreases, the attack becomes slower.
Depending on how the modulator operators are being used, it may be neces-
sary to decrease R1 for modulator operators as well.
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