Yamaha MU128 Owner's Manual page 41

Changing the Play Mode Display
The MU128 lets you view the Parts of the Performance in two ways, depending
on your preference.
Press the [PLAY] button repeatedly. Each press of the [PLAY] button switches
between the two displays below.
Performance number and name are indicated.
Voice names which make up the Performance are indicated.
MU128 Guided Tour
Selecting and Playing Individual Voices
41