Yamaha DX7 II FD Reference Manual page 30

Pmod The Pmod (pitch modulation) parameter adjusts the intensity ofLFO vibrato effect as it is
invoked by the breath controller or aftertouch. As the value of this parameter increases, so
does the range over which the pitch is modulated by the LFO whenever breath controller
or aftertouch are used.
0 BC or AT will not invoke pitch modulation at all.
99 Pitch modulation will be at maximum amplitude when BC or AT is applied.
Remember that the PMS parameter must be adjusted accordingly if you plan to use breath
controller or aftertouch to invoke vibrato.
Amod The Amod (amplitude modulation) parameter provides the same control over output level
modulation (tremolo or "wah-wah") as Pmod does over pitch modulation.
EGbias
0 BC or AT will not invoke level modulation at all.
9 9 Level modulation will be
at
maximum amplitude when BC or AT is applied.
Remember that the AMS parameter must be adjusted accordingly if you plan to use breath
controller or aftertouch to invoke tremolo, "wah-wah," or other output level modulation
effects.
The EGbias parameter provides direct breath or aftertouch control over the output level of
operators whose AMS parameter has been adjusted to a high value. This function does not
involve the LFO at all.
0 BC or AT have no effect on the output level of operators with appropriate AMS
values.
99 BC or AT have maximum effect on the output level of operators with appropriate
AMS values.
This parameter allows you to regulate changes in the volume or timbre of a voice with the
breath controller or aftertouch.
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