MIDI - Musical Instrument Digital Interface.

Since the MIDI 1.0 Specification combines timing clock information with and extensive protocol for communicating performance actions, the recording and replaying of MIDI data is a natural extension of the interface concept. 

MIDI recorders - more commonly termed sequencers - are MIDI's version of tape recorders.  Capable of storing and reproducing virtually any event of command that can be transmitted by MIDI, they offer significant advantages in both studio recording and live performance.  Playback may be synchronized with either an internal or an external time standard;  the playback rate may be altered without affecting musical pitch; and recorded events may even be reassigned to different instruments or sound programs.

The MIDI out of a master unit that can generate the requisite MIDI control data is connected to the MIDI In port of a sequencer unit.  The sequencer's MIDI Out is then routed back to the master unit, whose MIDI Thru may be connected to other MIDI equipped slave devices.

In recording mode, performance actions originating at the master are converted to MIDI data and sent to the sequencer, which memorizes them in relation to an internal timing reference.  the contents of the sequencer's memory can then be saved to a storage device (normally, a floppy disk or hard disk drive) for later recall.

In Playback mode, the sequencer reproduces the recorded MIDI data at its MIDI Out, with events again being timed in relation to its internal clock reference.  The sequencer data passes back to the master's MIDI In port and, optionally,  is echoed to other devices by its Thru port.  The master reproduces the recorded performance actions, as do any slave units chained to it.

For greatest operational flexibility and ease of use, MIDI sequencers are modeled on the multitrack tape recorder.  A sequencer may have a from one to a hundred or more tracks (as with audio tape decks, the number is usually finite).  These tracks record MIDI data rather than audio information, and are sometimes called vertual tracks because they reside in digital memory rather than on tape.

All of the track functions normally associated with multitrack recording may be perfromed with a MIDI sequencer.  Tracks can be overdubbed in synch with previously-recorded material.  Individual tracks can be soloed or muted in playback.  Data can be bounced from two or more tracks to another in order to free up track space.

The similarity ends at the concept of channels.  In an audio tape recorder, a track is a channel.  In a MIDI sequencer, data on one or more tracks may be freely assingned to any of the sixteen MIDI channels.  Moreover, a sequencer track can be made (through track bouncing) to contain events assigned to two or more channels at once,  because the MIDI protocol tags each individual event with channel data.

In MIDI sequencers, then, channels and tracks are entirely seperate things.  A channel is a routing assignment for a particular set of MIDI data; channels are asociated with specific receiver instuemnts, and thus with particular sounds.  A track, by contrast, is simply a container for holding recorded MIDI data; the data's channel assignment can be independent of it's track assinment.

The multitrack model brings a great deal of flexibility to MIDI sequencing.  For example, it is often impractical to store in one pass all of the events (such as fader moves or keystrokes) that you want a particular device to execute.  As with conventional multitrack recording, you can overdub two or more successive passes on seperate tracks, assigning both to the sam MIDI channel to create a composite effect.  You may then elect to merge the two tracks, or yoiu can keep them separate for editing purposes.

Some sequencers feature multiple MIDI Out ports, with the ability to reoute individual tracks to any of the ports.  This capability can extend MIDI beyond its sixteen-channel limitation, allowing very complex effects.

I know this may seem a little complex but trust me, once you've gone through it  few times, it will be simple.  Get to work!!!

Information for the article was gathered using the YAMAHA Sound Reinforcement Handbook.