If the volume level is too high, the sound may be affected by distortion or clipping.
Play a track and check the following:
1) Check the channel level indicator
Adjust the [TRIM] knob so the channel level indicator lights up with the peak level at around
 dB (so that the red light doesn't turn on).
2) Check the master level indicator
Adjust the [LEVEL] knob for MASTER so the master level indicator lights up with the peak level at around  dB (so that the red light doesn't turn on).
If distortion and sound clipping doesn't improve, the output level may exceed the allowable input level of the connected speaker or amplifier.
In this case, you'll need to lower the output level of [ATT.].
For details, see [UTILITY settings] in [Settings] in the Instruction Manual.
You can read the Instruction Manual [here].