Roland HP507 用户手册

You can play two tones simultaneously from each note of the keyboard. This feature is called “Dual Play.”
As an example, here’s how to layer piano and strings tones.

Both buttons will light.
When you play the keyboard, you’ll hear both the piano and the strings tones.

*  Dual play is not available if Split Play (p. 20) or Twin Piano (p. 24) are turned on.
*  For some combinations of sounds, the effect is not applied to tone 2, and this may affect how the tone sounds.
*  It’s not possible to layer Piano [Grand] and Piano [Early] tones together.

Left tone button

Press the [–] [+] buttons.

Right tone button

While holding down the tone button for Tone 2 (the right-most of the lit Tone buttons), and press the [–] [+] buttons.

Changing the pitch of tone 2 in steps of an octave: 

“Octave Shift” (p. 49)

Specifying the part(s) affected by the damper pedal: 

“Damper Pedal Part” (p. 49)

Adjusting the volume balance of the two tones: 

“Dual Balance” (p. 48)

Some of the tones provide a wide variety of other “effects” that can modify the sound in various ways.
The rotary effect is one of these effects.