Following on from last month, we continue our glossary of MIDI terms...

MIDI Controller

Any MIDI device which is being used to transmit MIDI information is generally called a MIDI Controller. Examples such as keyboards and MIDI drum pads are the obvious ones, but don't forget guitar synths and wind instruments - in fact all instruments capable of outputting MIDI data. Incidentally, in MIDI terms, if a keyboard has on-board sounds it is generally referred to as a synthesiser. If, however, it has no sounds of its own, it is termed a Master or Mother keyboard and usually has a superior MIDI specification than a conventional synthesiser.

MIDI Control Changes

MIDI Control Changes are often referred to as MIDI Controllers which, of course, confuses them with the instruments covered by the previous definition. MIDI Control Changes are, in fact, data messages used to alter performance aspects of an instrument or other MIDI-equipped device. For instance, MIDI Control Change 1 refers to MIDI Modulation. Moving the modulation wheel on a synth causes MIDI Control Change data to be sent out from the MIDI Out port to whatever MIDI device is receiving - another synth or perhaps a sequencer.

MIDI Control Change 7 is called MIDI Volume and, as you might expect, is used to vary the level of signal from a MIDI-equipped device. Another common one is 64 - MIDI Sustain Pedal - transmitted every time you put your foot down on a keyboard's sustain pedal.

In all, there are a total of 128 MIDI Control Changes, out of which eight are used for special MIDI Mode messages and various others are, as yet, undefined.

Omni On/Off

You'll see this phrase quite often in a MIDI context. Omni On literally means 'All on' and indicates that a MIDI device will recognise MIDI information received on any of the 16 MIDI channels. Some early synths - Yamaha's DX7 - operated only in this manner. Nowadays, with so many multi-timbral synths being available, Omni Off mode is nearly always the default setting, in order that each voice responds only to the data sent to it via the selected MIDI channel.

MIDI Program (or Patch) Changes

In order to individually select the onboard voices or 'patches' on a synth or sound module, a series of push buttons or increment/decrement controls are included. The action of these controls may be duplicated via MIDI through the use of MIDI Program Change messages.

On a conventional synth, a MIDI Program Change message is sent every time a patch button is pressed - thus, a single button push can be made to call up patches on a variety of different MIDI devices, including signal processors which use Program Changes messages to select between their onboard effects patches. The standard MIDI specification allows for a total of 128 (0-127) Program Changes - though care needs to be exercised as different manufacturers use different numbering systems and conversion may be necessary.