Yamaha MU80 Owner's Manual page 109

Mute Lock
This determines whether or not the Part Mute status of the MU80 is
reset when receiving a GM System On or XG System On message.
Generally, this message is automatically transmitted to the MU80 as
part of General MIDI song data. When Mute Lock is set to off, this
resets the Mute status of the Parts on the MU80. If you want to keep
the current Mute settings and disable this reset, set Mute Lock to on.
(For more information on the Mute function, see page 23.)
A/D Part Lock
This determines whether or not the current parameter values and
Variation effect settings of the A/D Parts are reset when receiving a
GM System On or XG System On message. If you want to keep
the current parameter values and Variation settings of the A/D Parts,
set Mute Lock to on. (This parameter has no effect in the Perform-
ance mode.)
UTILITY MODE
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