One of several ways in which a device can respond to incoming MIDI information. There are two parts to each mode, one defining whether it is monophonic or polyphonic, and the other determining if it is multitimbral or not. Four modes are included in the MIDI spec, and two others, Multi Mode and Mono Mode (for MIDI guitar) were developed later.

1. Omni On/Poly – Device responds to MIDI data regardless of channel, and is polyphonic. (See WFTD “Polyphonic“)
2. Omni On/Mono – Device responds to MIDI data regardless of channel, and is monophonic. This mode is rarely, if ever, used.
3. Omni Off/Poly – Device responds to MIDI data only on one particular channel, and is polyphonic. This is the normal mode for most keyboards that are not functioning multitimbrally.
4. Omni Off/Mono – Device responds to MIDI data only on one particular channel, and is monophonic.

Multi Mode – Used by many devices for multitimbral operation. An expanded version of Mode 3, Multi Mode allows the device to respond to several independent MIDI channels at once, with each being polyphonic. (See also WFTD “Multitimbral“)

Mono Mode – Used for MIDI guitar applications, Mono Mode is an expanded version of Mode 4, allowing for six Omni Off/Monophonic channels to be used at once, one for each string of the controller. This allows for better tracking, independent pitch bend per channel, and a separate sound or patch assignment per channel.