36. MIDI Modes
How a MIDI instrument responds to a MIDI message depends upon what mode it has been set to. All instruments capable of responding to MIDI data are set to a MIDI mode that determines their particular response to data.
There are four modes of reception described in the original MIDI specification. In addition, there is an extended version of one of these modes, so that a MIDI instrument may actually respond to incoming data in five ways. These modes are most applicable to sound-producing modules that respond to Note On/Note Off messages because each describes the number of notes that may be played simultaneously by a sound-producing module. How an instrument responds in each of these modes is detailed below.
1. An instrument is set to Mode 1, also called Omni On, Poly, when it is enabled to respond to more than one note, or more than one note at a time, without regard to the channel on which the message is transmitted. Also called Omni mode.
| Mode 1 | Also called: OMNI ON, POLY |
| Omni On | Responds to All MIDI Channels |
| Poly | Responds to One or More Notes Simultaneously |
2. An instrument is set to Mode 2, also called Omni On, Mono, when it is enabled to respond to only one note at a time without regard to the channel on which the message is transmitted.
| Mode 2 | Also called: OMNI ON, MONO |
| Omni On | Responds to All MIDI Channels |
| Mono | Responds to Only One Note at a Time |
3. An instrument is set to Mode 3, also called Omni Off, Poly, when it is enabled to respond to more than one note, or more than one note at a time, and only on the single channel on which the message is transmitted. Also called Poly Mode.
| Mode 3 | Also called: OMNI OFF, POLY |
| Omni Off | Responds to Only One MIDI Channels |
| Poly | Responds to One or More Notes Simultaneously |
4. An instrument is set to Mode 4, also called Omni Off, Mono, when it is enabled to respond to only one note at a time and only on the single channel on which the message is transmitted. Also known as Mono mode.
| Mode 4 | Also called: OMNI OFF, MONO |
| Omni Off | Responds to Only One MIDI Channels |
| Mono | Responds to Only One Note at a Time |
5. Not defined in the original MIDI specifications, this fifth mode is often called Multi-mode. In this mode a sound-producing module acts as if it is more than one sound-producing module responding often to sixteen, but sometimes eight, channels simultaneously, with a different timbre on each channel. A sound-producing module in Multi-mode responds like multiple sound-producing modules set to Poly mode.
| Mode 5 | Also called: MULTI-MODE |
| Multi | Responds to Multiple MIDI Channels Simultaneously |
| Poly | Responds to One or More Notes Simultaneously |
All MIDI instruments are not capable of responding to all MIDI messages. Some of the early sound-producing modules were made not to be velocity-sensitive, or to be unresponsive to certain control messages. This made the instrument less expensive to manufacture and resulted in a lower price to consumers. Some contemporary instruments are designed to respond to many types of MIDI messages and command a high price, while others respond to fewer messages and are designed to appeal to a less expensive retail market. This strategy is obviously meant to interest the widest variety of consumers in the marketplace. Fortunately the MIDI protocol is intelligent enough in that any instrument receiving a MIDI message for which the instrument has not been designed will ignore the message with no harm done.
