MIDI
MIDI stands for Musical Instrument Digital Interface and refers to the protocols, interfaces, and physical connectors used for audio devices to communicate musically relevant information. MIDI does not transmit audio signals but information used to create them.
Contents
Structure of MIDI Information
MIDI transmits data as digital electronic pulses in serial. Although MIDI cables commonly connect via a 5-pin jack, often only 3 are used - two for power, and one for data.
Channels
Every MIDI link can carry up to 16 different channels of data. Each device typically "listens" and "speaks" on only one of these channels. This allows MIDI data to be sent along a common cable chain through many devices while targeting different messages for different devices, avoiding the use of patch bays and manually managing loops/sends between devices.
Messages
MIDI sends all its information as messages, which are composed of multiple MIDI bytes. A normal byte is 8-bits, but a MIDI byte is 10-bits, comprised of a start/stop bit, a type bit, and a 7 bit value. The type bit indicates whether the byte is a status byte or data byte. A typical MIDI message is composed of a status byte to indicate what type of message it is followed by 1-2 data bytes. MIDI messages can be one of the 5 types below, which are further broken down.
Channel Voice
This is the most common type of data you'd be expecting MIDI to transmit:
- Note-On w/ velocity and pitch (note number) values
- Note-Off
- Program Changes (PC's)
- Control Changes (CC's)
Notes are typically associated with MIDI controllers/keyboards or drum machines (or e-kits). For guitar, MIDI is useful to control devices, switching patches, switching effects on/off, or controlling effect parameters. PC's are used for changing patches, while CC's toggle and manipulate parameters. However, keyboards often come equipped with controllers that are designed to send CC messages - pitch and mod wheels, rotary dials, and sliders. As well as non-piano format notes: tap pads, and buttons.
Channel Mode
Channel Mode messages are designed to change the way devices respond to processing channel data. It can switch devices from listening to a single channel (Omni Off) vs. all channels (Omni On). It can also send note-off or reset to default messages to all controllers.
System Common
System Common messages are used to send system data that has no channel number and is sent to all devices.