Yamaha SY55 Product Manual page 21

Voice Numbers 63 and
Although most SY55 voices have a 1, 2 or 4-element configuration (we'll
64 are Drum-set Voices learn more about elements in the "EDITING VOICES" section, beginning on
page 35), voices 63 and 64 in any voice bank are special drum-set voices that
essentially have a 61-element configuration. Each element, in this case, corre-
sponds to a different key on a keyboard. A range of high-quality drum and
percussion waveforms can be assigned to the different elements/keys and
handled as a single voice — i.e. each key plays a different instrument within
that "drum set."
The drum-set voices are particularly useful with the SY55's MULTI PLAY
mode and sequencer, described in the following two sections.
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