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CHANNEL MODES

Synthesizers contain sound generation elements called voices. Voice assignment is the algorithmic process of routing Note On/Off data from the keyboard to the voices so that the musical notes are correctly played with accurate timing.

When MIDI is implemented, the relationship between the sixteen available MIDI channels and the synthesizer's voice assignment must be defined. Several Mode messages are available for this purpose. They are Omni (On/Off), Poly, and Mono. Poly and Mono are mutually exclusive, i.e., Poly Select disables Mono, and vice versa. Omni, when on, enables the receiver to receive Voice messages in all voice Channels without discrimination. When Omni is off, the receiver will accept Voice messages from only the selected Voice Channel(s). Mono, when on, restricts the assignment of Voices to just one voice per Voice Channel (Monophonic.) When Mono is off (=Poly On), any number of voices may be allocated by the Receiver's normal voice assignment algorithm (Polyphonic.)

For a receiver assigned to Basic Channel "N," the four possible modes arising from the two Mode messages are:
 
 

Mode

Omni

Poly

Description

1

On

Poly

Voice messages are received from all Voice channels and assigned to voices polyphonically.

2

On

Mono

Voice messages are received from all Voice Channels, and control only one voice, monophonically.

3

Off

Poly

Voice messages are received in Voice channel N only, and are assigned to voices polyphonically.

4

Off

Mono

Voice messages are received in Voice channels N thru N+M-1, and assigned monophonically to voices 1 thru M, respectively. The number of voices M is specified by the third byte of the Mono Mode Message.

Four modes are applied to transmitters (also assigned to Basic Channel N). Transmitters with no channel selection capability will normally transmit on Basic Channel 1 (N=0).
 
 

0

Mode

Omni

Poly

Description

1

On

Poly

All voice messages are transmitted in Channel N.

2

On

Mono

Voice messages for one voice are sent in Channel N.

3

Off

Poly

Voice messages for all voices are sent in Channel N.

4

Off

Mono

Voice messages for voices 1 thru M are transmitted in Voice Channels N thru N+M-1, respectively. (Single voice per channel).

A MIDI receiver or transmitter can operate under one and only one mode at a time. Usually the receiver and transmitter will be in the same mode. If a mode cannot be honored by the receiver, it may ignore the message (and any subsequent data bytes), or it may switch to an alternate mode (usually Mode 1, Omni On/Poly).

Mode messages will be recognized by a receiver only when sent in the Basic Channel to which the receiver has been assigned, regardless of the current mode. Voice messages may be received in the Basic Channel and in other channels (which are all called Voice Channels), which are related specifically to the Basic channel by the rules above, depending on which mode has been selected.

A MIDI receiver may be assigned to one or more Basic Channels by default or by user control. For example, an eight-voice synthesizer might be assigned to Basic Channel 1 on power-up. The user could then switch the instrument to be configured as two four-voice synthesizers, each assigned to its own Basic Channel. Separate Mode messages would then be sent to each four-voice synthesizer, just as if they were physically separate instruments.



CHANNEL MODE MESSAGES
 

Status

Data

Hex

Description

1011nnnn

0ccccccc 0vvvvvvv

 

Mode Messages 

 

ccccccc = 122

 

Local Control

 

vvvvvvv = 0

 

Local Control Off

 

vvvvvvv = 127

 

Local Control On

 

ccccccc = 123
vvvvvvv = 0

 

All Notes Off

 

ccccccc = 125
vvvvvvv = 0

 

Omni Mode On 
(All Notes Off)

 

ccccccc = 126
vvvvvvv = M
vvvvvvv = 0

 

Mono Mode On (Poly Mode Off)
(All Notes Off)
where M is the number of channels.

 

ccccccc = 127
vvvvvvv = 0

 

Poly Mode On (Mono Mode Off)
(All Notes Off)

NOTES:

  1. nnnn: Basic Channel # (1-16, coded as defined in Table I)
  2. Messages 123 thru 127 function as All Notes Off messages. They will turn off all voices controlled by the assigned Basic Channel. Except for message 123, All Notes Off, they should not be sent periodically, but only for a specific purpose. In no case should they be used in lieu of Note Off commands to turn off notes which have been previously turned on. Therefore any All Notes Off command (123-127) may be ignored by receiver with no possibility of notes staying on, since any Note On command must have a corresonding specific Note Off command.
  3. Control Change #122, Local Control, is optionally used to interrupt the internal control path between the keyboard, for example, and the sound-generating circuitry. If 0 (Local Off mesage) is received, the path is disconnected: the keyboard data goes only to MIDI and the sound-generating circuitry is controlled only by incoming MIDI data. If a 7FH (Local On message) is received, normal operation is restored.
  4. The third byte of "Mono" specifies the number of channels in which Monophonic Voice messages are to be sent. This number, "M", is a number between 1 and 16. The channel(s) being used, then, will be the current Basic Channel (=N) thru N+M-1 up to a maximum of 16. If M=0, this is a special case directing the receiver to assign all its voices, one per channel, from the Basic Channel N through 16.


 

Introduction & Conventions
Hardware
Message Types
Data Types
Channel Modes
Summary of Status Bytes
Channel Voice Messages
System Common Messages
System Real Time Messages
System Exclusive Messages
Controllers
 

 
 
 

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