Roland HP-1 Owner's Manual page 10

Main operations
Playing two sounds at a time ("Dual")
It is also possible to play two Tones simultaneously (something we like to call "Dual mode"). A popular combination is
piano with strings, but feel free to try out other combinations.
A
B
C
1. Hold down the Tone button of the first sound you
wish to use while pressing the Tone button of the
sound you want to add.
This only works for Tones that can be accessed via the
front panel (i.e. not for the "second" Tone set whose
names are printed below the keys).
You can also modify the balance of the two Tones:
2. Simultaneously press [Demo] and [Reverb] to
enter Function mode (both indicators flash).
3. Press the "G7" or "G#7" key.
10
Press the white "G7" key to increase the volume of the
Tone assigned to the "left button" ([Piano1] in the
above example).
Press the black "G#7" key to increase the volume of the
Tone assigned to the "right button" ([Strings] in the
above example).
4. Press [Demo] and [Reverb] again to leave the
HP-1's Function mode.
Note: You have to leave Function mode in order to hear
what you are playing.
Right sound louder
Left sound louder