MIDI Messages

When you press a key on your keyboard to trigger a note on another synth, you are sending a single MIDI event. All MIDI messages are made up of a series of “words” of binary information. So each note you play constitutes a single event. MIDI uses a serial interface (like a Modem) that operates using a bandwidth of 31.25 Kbps (thousand bits per second). There are five types of MIDI messages:

Channel Voice Messages: These are performance messages and convey note on/off information. They can use all sixteen MIDI channels with each channel being polyphonic. Channel Voice Messages send information such as notes played, sustain pedal, breath controllers, aftertouch, pitch bend, and modulation.

Channel Mode Messages: This type of message allows you to specify which MIDI channel the data will be sent on and what patch number (sound) the receiving synth will use to execute the message. In other words, Channel Mode Messages tell a synth how to respond to incoming MIDI data. There are four types of Channel Mode Messages; OMNI ON/POLY, OMNI ON/MONO, OMNI OFF/POLY, and OMNI OFF/MONO. To illustrate, a synth set to OMNI ON/POLY will respond to all incoming MIDI data regardless of the MIDI channel and will play as many notes as it’s polyphony will allow. OMNI ON/MONO will respond to all data, but only play one note at any given time. OMNI OFF/POLY or MONO will allow a synth to respond to a specific MIDI channel (whatever it is set to) and play either it’s maximum polyphony or a single note respectively. Most synths default to the MIDI Mode OMNI ON/POLY.

Another type of Channel Mode Message is the LOCAL CONTROL ON/OFF message. This allows you to “disconnect” a synth’s keyboard from its internal voices. When using a sequencer, your master keyboard should most likely be set to LOCAL OFF so you can control other instruments in your MIDI setup without triggering notes on the master keyboard. The sequencer can be configured to send note on/off information to the master keyboard when you wish so you will still have access to its voice capabilities.

System Common Messages: If your synth can store song information, these message types allow you to choose which song from the synth’s memory will be played and at what point in the song play will begin. Not all MIDI devices utilize this feature of MIDI.

System Real Time Messages: Handles all data that is related to synchronization and timing. These messages are MIDI CLOCK, START, STOP, CONTINUE, ACTIVE SENSING (to verify proper MIDI connections), a SYSTEM RESET. Although not all synths respond to SYSTEM RESET, be careful with this one, as it returns a synth to its factory default settings.
System Exclusive Messages: This type of message transmits information to a specific brand of synthesizer. Each manufacturer will hard-code MIDI messages that are unique to the device. Using these messages, you can send configuration information to your synth that is unique to its make and model. An example would be uploading a new bank of sounds to your synth on the fly just before a sequence begins to play.

Ultimately, it is the System Exclusive Message set in the MIDI Specification that allows you to effectively manage a complex MIDI setup. But, alas, there are limitations as we discuss in the next section.

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