Yamaha DX7 II FD Reference Manual page 31

Pbias The Pbias (pitch bias) parameter enables you to produce pitch bend effects using the
breath controller or aftertouch. The value of this parameter determines the pitch bend
range and direction.
-50 Application of BC or AT produces maximum pitch bend downward.
0 Application of BC or AT produces no pitch bend.
+50 Application of BC or AT produces maximum pitch bend upward.
This is handy when you are playing the keyboard with both hands and need to bend the
pitch.
Modulation wheel
This LCD display allows you
to
program the modulation wheel parameters. They are
identical
to
the breath controller and aftertouch parameters with the exception that there is
no Pbias. This means that you can program the modulation wheel
to
invoke pitch
modulation, amplitude modulation, and direct output level control. It cannot be
programmed to produce pitch bend; this is accomplished with the neighboring pitch bend
wheel.
In the descriptions of the Pmod, Amod, and EGbias parameters above, simply substitute
the words "modulation wheel" for "breath controller or aftertouch." These descriptions
will then relate to the modulation wheel.
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