I'll try to describe it. The Musical Instrument Digital Interface (MIDI) enables people to use multimedia computers and electronic musical instruments to create, enjoy and learn about music. There are actually three components to MIDI, which are the communications Protocol (language), the Connector (hardware interface) and a distribution format called Standard MIDI Files.
If you have a sound card and a midi browser plugin, you have the ability to play standard midi files though they may sound very cheezy as most sound cards (low cost) do not have very good instrument samples in them. MIDI is used quite extensively in the studio, Paul used it to compose Standing Stone.
A typical setup is a computer so to composed and edit the tracks (Cakewalk Pro or Sonar), a sound module (Rolland SC-88) and an input device like a keyboard (Rolland A-30). Though they have drums, sax and special pickups for guitars so to use as an input device. A properly produced midi song should have all the instruments on separate tracks. I only have a keyboard so I input all the instruments on the keyboard and then fine tune the sound during editing.
My method of sequencing has changed since the 1st one I did. Eleanor Rigby was my first song and it was a combined version of the original Beatles and Paul's version from Broadstreet. You have to listen and learn each instrument then lay the tracks down. Depending on what instrument I decide to play live with, I omit either the bass or the guitar I wish to play.
I'm not a tremendous keyboard play by any means as I just know basic chords but with a good ear and persistence you get some very good sounding music. There is a lot of crappy sounding midi out there that doesn't sound anywhere near the off-the-record sound, but there also is some very good quality songs already sequenced. I must say that Tibe surely does produce some fine sequences.
For example when I did a George Harrison tribute during one of my gigs last year, I found Isn't it a Pity, My Sweet Lord and All Things Must Pass. All 3 had the basics in them but the tracks were lacking so I edited the hell out them, replacing the bass tracks and improving the drums, strings etc. which made them sound much closer to the album.
I don't have much time to sequence but I did start "I Do" and "Freedom" but haven't finished them yet. With the more advanced software like Cakewalk Sonar, you can actually record an audio track of the original song and then use it as a basis to listen and duplicate the instrument on another track.
With MIDI I have co-ordinated MIDI controlled lights so to turn on/off/fade sequence precisely in songs, also because of MIDI I can controll effects so when I do Juniors Farm and then at the end where there is all the phase shift, I have programmed precisely at that part for the sound board to automatically change to the proper amount of phase shift on the vocals and desired instruments.
I've been meaning to re-produce all the sequences but alas the time. I haven't heard any of the newer sound modules but they have made some improvements on the samples.
Back to the sequences, I've produced a lot myself but I have also purchase some as there was a release of some very, very good official McCartney sequences from Tune 1000 that needed some minor fine tuning, and some simply downloaded from the net. I've sequence six or seven Badfinger songs as well as some Eagles tunes.
Sorry for rambling on.