Roland HP505 Owner's Manual page 29

Using the sound of a specific part as a "guide" (mute volume)
If desired, you can specify that the sound of a part will play at a reduced volume rather than going completely silent when you press a part button
and turn off its indicator.
This setting lets you play a specific part at a reduced volume and use it as a "guide" for your playing.
1.
While holding down the part button, press the [–] [+] buttons .
Screen Value Explanation
0–10
Higher values make the sound louder.
(default: 0)
1
Practicing
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