Kawai Novus NV10 Owner's Manual page 66

Concert Magic
 Adjusting the Concert Magic song balance
It is also possible to adjust the volume balance between the right-hand and left-hand parts of the current Concert Magic song,
allowing each hand to be practiced separately when using the playback function.
1. Tap the [Menu] button to show the Concert Magic settings
menu.
2. Long press and drag the Balance slider to the left-most
position (9-1).
The right-hand part of the selected Concert Magic song will
be muted, allowing this part to be practiced.
3. Long press and drag the Balance slider to the right-most
position (1-9).
The left-hand part of the selected Concert Magic song will be
muted, allowing this part to be practiced.
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Balance slider