Yamaha SY99 Owner's Manual page 191

MULTI PLAY MODE
Multi mode allows the SY99 to function as sixteen completely independent synthesizers, each being con-
trolled on its own MIDI channel. Since the keyboard of the SY99 transmits only on one MIDI channel at a
time, multi mode is meaningful only when you are using a sequencer (either the SY99's built-in sequencer or
an external MIDI sequencer) to send two or more channels of MIDI data to the SY99's tone generator.
Note: If a multi contains many two-element or four-element voices, the response to Note-on messages may become
slightly slower. If this is a problem, either reduce the number of voices in the multi, or select voices which use
fewer elements.
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