MIDI (Musical Instrument Digital Interface) is a communication protocol for musical instruments. This industry standard enables connections between a variety of devices from different manufacturers. Examples of MIDI-compatible equipment include synthesizers, drum machines, MIDI patch bays, effects processors, MIDI interfaces, and MIDI sequencers.

MIDI devices are equipped with 5-pin DIN connectors, labeled as either IN, OUT, or THRU. The MIDI OUT port transmits messages. The MIDI IN port receives messages. The MIDI THRU outputs whatever is received from the IN port. MIDI devices are connected with MIDI cables that are available at most music stores.

USB and FireWire-compatible MIDI devices send and receive MIDI messages to and from the computer over USB or FireWire.

The MIDI protocol provides 16 channels of MIDI per port. A single MIDI cable can transmit a separate set of messages for each of the 16 channels. These 16 channels can correspond to separate MIDI devices or to multiple channels within a single device (if the device is multitimbral). Each channel can control a different instrument sound.

Pro Tools | First provides powerful MIDI sequencing capabilities. You can record, enter, edit, and play back MIDI data on Pro Tools Instrument and MIDI tracks. These actions can be done in the Edit window, the MIDI Editor window, and the MIDI Event List.

MIDI data in Pro Tools | First can be anything from MIDI note data (note number, on/off, velocity) to System Exclusive (Sysex) messages. MIDI data can be recorded or played back from both external MIDI devices with a MIDI interface and other MIDI software (such as instrument plug-ins and ReWire client applications).