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Chapter 12: MIDI Functions
ANDROMEDA A6 REFERENCE MANUAL 251
Channel Messages: Mode Messages
There are four types of messages that determine the MIDI Mode of the instrument.
The “mode” of a device refers to how it will respond to incoming MIDI data.
The four possible modes are defined by the instrument’s Receive Status – Omni On or
Omni Off – and by it’s Voice Assignment – Poly or Mono.
The Omni On or Omni Off messages determine how many channels will be
recognized when the instrument or device is receiving MIDI data. Omni On means
that data from all channels will be received; Omni Off tells the receiving instrument
to respond to MIDI data on one channel only.
The Poly and Mono messages determine the voice assignment of the instrument. An
instrument’s voice is the most basic unit of sound generation. It can be an integrated
circuit chip (or chips) like the A6, or can be a sampled sound in the instrument’s
memory.
Each voice plays one note at a time, so the number of notes you can play at one time
will be limited by the number of voices. The A6 is a 16-voice instrument so you can
play up to 16 keys on its keyboard, receive up to 16 MIDI Notes, or a combination of
16 keyboard and MIDI Notes at one time.
So in Poly mode, the receiving instrument plays incoming MIDI notes
polyphonically up to the number of voices it has (16 maximum for the A6). In Mono
mode, the receiving instrument plays incoming MIDI notes monophonically: only
one voice at a time plays in response to incoming MIDI notes.
The MIDI Specification combines the two Receive Status modes with the Voice
Assignment modes and describes each as follows:
Mode 1: Omni On/Poly
The instrument responds to notes from all Channels and plays them polyphonically.
This is a popular mode for many musicians in that it makes the unit play via MIDI
regardless of what Channel other units in the MIDI system are set to. Most products
ship from the factory with this mode enabled so that they will respond to MIDI
polyphonically right out of the box.
Mode 2: Omni On/Mono
The instrument responds to notes from all Channels and plays them monophonically
on one voice. This mode causes the receiving instrument to be monophonic and is the
least used mode of the four.
Mode 3: Omni Off/Poly
The instrument responds to notes from one Channel only (which is set by the user)
and plays them polyphonically. This is possibly the most-used mode for the majority
of musicians. In most MIDI systems, each instrument is set to play polyphonically on
a specific MIDI Channel.
Mode 4: Omni Off/Mono
In this mode, the receiving device is, in essence, divided into a number of
monophonic instruments: each voice is assigned its own MIDI Channel and will play
only one note at a time when incoming MIDI Notes are recognized.