34. MIDI System Connections

MIDI instruments are connected one to another by means of a MIDI cable.

Diagram 34-1: A MIDI cable.

There will be at least one MIDI port on all MIDI instruments that will accept the MIDI cable plug. These MIDI ports, which look the same on the outside, will be one of three varieties: MIDI OUT, MIDI IN, or MIDI THRU.

Diagram 34-2: The MIDI ports.

Each MIDI port has a different function. The MIDI OUT port is the port from which MIDI messages are transmitted, but only if the information originated in that instrument. The MIDI IN port is the port through which data is received. Information may not be received through any other port. The MIDI THRU port outputs a replica of any MIDI data received at the MIDI IN port. This replica signal is output virtually at the instant it is received.

A musician might connect a keyboard controller in series to three sound-producing modules. In such a setup, sometimes called a daisy chain, a MIDI message from the keyboard controller is sent out its MIDI OUT port to the MIDI IN port of a sound module . A replica of this MIDI message is then sent out the MIDI THRU port of the sound module to the MIDI IN port of a second MIDI device. This second device then passes on a copy of that MIDI message via its MIDI THRU port to the MIDI IN yet another MIDI device.

Diagram 34-3: A daisy chain.

The components of a MIDI system can be connected together in many ways, and often a sequencer is part of a MIDI configuration. Frequently, the MIDI OUT port of a keyboard controller is connected to a computer running a sequencing software program via the MIDI IN port of a MIDI interface, which is a device that assists and permits the flow of MIDI data to and from the computer and the instruments in the MIDI system. The MIDI interface is a veritable extension of the computer. Once the MIDI data is received by the computer's sequencing program, the data can be sent out the MIDI OUT ports of the MIDI interface to the instruments in the system. In addition to the traditional MIDI connections discussed above, it is currently common for MIDI to also use USB (Universal Serial Bus) to connect devices to a host computer.

Diagram 34-4: A MIDI interface.