Yamaha SY77 Operating Manual page 172

MULTI EDIT MODE
From multi play mode press EDIT to enter multi edit mode. Unlike voice edit mode, multi edit mode has only
a single job directory.
You can use the SEQUENCER control keys to playback sequencer song or sequencer pattern data while
editing a multi. It is especially helpful to play a sequencer song back while editing a multi, since you will be
able to hear the effect your modifications are having on each of the voices. For example you can edit multi
parameters to modify the "mix", or even edit a voice, all while the song is playing.
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