Yamaha DX7 II FD Reference Manual page 37

Dual detune
Split point
This parameter appears only in dual voice mode. Its function is similar to that of the
oscillator detune parameter. Instead of affecting the frequencies of the operators within
one voice, the dual detune parameter shifts the pitch of the two voices away from each
other.
0 Voices A and B are not detuned with respect to each other.
7 Voices A and Bare detuned by Y4 of a semitone (25 cents).
This parameter is used to achieve a richer sound and chorus effects, particularly with
ensemble voices such as brass, strings, and electric organ.
Effective only in the split voice mode, this parameter determines the key which divides
the keyboard between voices A and B. Voice A is always controlled by the lower half of
the keyboard, including the split point key.
C-
2
Set split point at C-2.
G8 Set split point at G8.
Setting this parameter can be accomplished using the + 1/-1 buttons or the data entry
slider. In addition, it can be set using the keyboard itself. With the split point parameter in
the LCD display, simply play the key you wish to be the split point.
To change the split point in the same way after selecting it in this manner, you must cycle
through the LCD displays by repeatedly pressing the voice mode button (#28) until the
split point display appears again. A new split point can then be selected by playing any
key on the keyboard. The+ 1/-1 buttons and the data entry slider can be used to change the
split point at any time.
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