The MASTER Mode is the mode that allows you to organize everything you need to do. It lets put the various programs you wish to use in a single bank of 128. Say you are on stage, you need an acoustic piano for the first composition, then you need an electric piano layered with strings, followed by setup where you have a bass in your left hand, organ and brass in your right, and you end the set by playing back a multi Part sequence from your computer where there are 12 Parts pre-recorded and lastly you return to a solo flute sound to end the set.

This means you might have to move from Voice mode to Performance mode, then to a Multi and finally back to Voice mode... Or you can put these various programs in order so all you need to do is press a foot switch to advance through MASTER mode. It allows you to place Voices, Performances, Multi setups together in a single easily accessible bank. Rather than jumping all over the place. It organizes your favorite things to do into a single list of programs. It also helps you, as the name implies organize external keyboards and modules too. When you call up a Master program 001-127, it can not only organize your internal setups but can do the same thing to external devices via MIDI. MASTER 001 might recall a piano Voice internally and shut off your external devices OUT via midi. The next MASTER 002 might recall and internal electric piano, while externally recalls a string sound on your external Midi module. Etc. Master mode - a single mode to organize your setups be they simple or very complex. It organizes Voices, Performances, and Multi Part setups into a single Bank.

MULTI mode lets the S90 XS receive on as many as 16 different Midi channels simultaneously in one setup. Normally, you play on one Midi channel at a time. But when you work with a sequencer you want to build up your composition one track at a time. So Multi mode, as the name implies, allows the S90 XS to receive via MIDI on 16 separate MIDI channels - from your external DAW (digital audio workstation) software, like Cubase. Each Multi setup could represent the instrumentation for a different ensemble of instruments. The S90 XS is said to be 16 Part multi-timbral, because on each of the 16 Midi channels you can put a different instrument. Used for recording sequences. You might put drums on 1, bass on 2, piano on 3, flute on 4, guitar on 5, strings on 6, brass on 7, percussion on 8, etc, etc., etc.

VOICE mode (a single sound).
PERFORMANCE mode a single program where you access as many as four Voices at once for real time play; splits, layers, split/layer combinations.
Both Voice and Performances are accessed on just one Midi channel.
Multi mode is 16 Midi channels.

oh I can finally understand something! thank you you're the best! I just want to understand a little 'more about the multi .. I did not understand what play the 16 voices that I imposed ...