Introduction
With the right software, Midifile backing tracks can be converted to mp3, but unfortunately mp3 backing tracks cannot be converted to midifile.

Midifiles need individual instrument data for each sound (drums, bass, piano, brass, strings etc), but you can't extract this individual instrument data from an mp3 file. This is because an mp3 file is a stereo recording which has had all the individual instruments in the song mixed together so they can't be seperated in to individual sounds. To best explain this, we should first look at the fundamental difference between a midifile and an mp3 file.

A midifile is multi-track arrangement whereas an mp3 file is a two track arrangement (ie stereo). A typical midifile may consist of up to 16 instruments (eg drums, bass, guitar, brass, strings, piano etc) each on their own individual midi channel. Although an mp3 file can consist of exactly the same number of instruments, the fundamental difference is that in an mp3 file these instrumets are all mixed together on two channels (stereo - left and right). Imagine you are baking a cake...you have all the ingredients to hand (flour, eggs, water, sugar etc). You can deal with each ingredient seperately and decide how much or how little of each ingredient you want to use. But once it's all mixed together in the bowl, you can't go back and take the eggs out of the mixture! So, in this sense, the midifile is like the individual ingredients, and the MP3 file is the mixture in the bowl.

My article on comparing MP3, CD, Minidisc & Midifile formats goes in to this subject in more detail and you should read through it if you are still in doubt as to the difference between backing track formats.

Midifile = Multitrack
If you have a song in midifile format, then by using a computer running the right type of software (or a hardware midifile player with editing facilities), each channel in that midifile can be isolated and treated seperately. You can change the volumes, notes etc of each and every instrument on those 16 midifile channels. Some entertainers who use midifiles will carry their midifiles and a keyboard or sound module to their gig. Others who don't want to carry around so much equipment will record the midifile to stereo beforehand (perhaps to mp3 or minidisc) so they only need to carry an mp3 player or minidisc player to their gig to play their tracks.

MP3 = Two-Track
Once a backing track is in a stereo format (mp3, CD, Minidisc, Cassette, DAT ) it is no longer a 16 track arrangement - it is now a two track arrangement (stereo means two track - left and right) so the instruments are all mixed in together and can no longer be isolated and individualy edited. If, for example, you tried to change the volume of the left and right channels of an mp3 backing track, then the voloume of ALL the instruments in the song would be affected. You can successfully make some changes to a stereo recording but they are always going to be "global" changes ie they affect the whole song. Changing the overall volume of a track is one such change that falls in to this category and also, to a lesser extent, is key changes - by changing the key on the left and right channels, you are changing the key on EVERY instrument on the recording, so it will work. Only problem with this though is that by changing the key down your tom tom drums may end up sounding like timpanis and changing the key up might make any backing vocals on the song sounding like the chipmunks!

If you've been reading through this article thus far, then you're most probably a midifile user and by now you'll be realising that midifiles are more flexible than mp3 files. So does that mean they're better? Well, don't be too hasty - there are some very major drawbacks to midifiles so read on before you abandon the idea of mp3 altogther...it's not as straightforward an argument as you may think...

Problems with midifiles
There are a number of drawbacks to using midifiles.

Drawback 1: Carrying back-breaking equipment to a gig.
Many years ago singers used to carry a mountain of equipment to gigs - a PA system, a bunch of midifiles, various keyboards and racks containing expanders (sound modules). But now you can get the exact same sound (well, actually a better sound), simply by turning up to gigs with a PA and an iPod in your top pocket!

Drawback 2: Good midifiles are hard to find.
If you've ever bought or downloaded midifiles from the internet you probably know by now that many of them are very poor representatives of the songs they are supposed to be(!). If you're not a musician it can take you forever to get the midifile to sound right and most times you end up having to ditch the idea altogether and try to find a better midifile.

Drawback 3: Inferior quality sounds.
A midifile is only as good as the sounds on the equipment you use to play it through. Unless you have access to high quality expensive sound sources and equipment like they use in professional recording studios, even the best midifile in the world will sound thin and "unprofessional". If you want to portray yourself onstage as a professional artist, your home-made midifile derived backing tracks can seriously affect your image. Remember, professional artists always use professional backing tracks...when was the last time you saw Madonna or Robbie Williams do a gig with a bunch of midifiles (try never...)! And don't think that big name artists always have an orchestra or backing band with them all the time. Most big name acts have to regularly turn up at promotional events and daytime TV studios and sing their latest song...without their band. To do that, they sing live but use a backing track for the music...and the backing tracks they use ain't no midifiles!

Conclusion
Despite the above drawbacks, the flexibility of midifiles still ensures that this type of file format for backing tracks remains popular with a small number of pub/club acts to this day even despite the fact that it has been overtaken by mp3 as the favourite playback format for professional entertainers. And for good reason - you may be surprised to know that you can actually still get that same midifile flexibilty from an mp3 file! I've written an article on backing track editing which goes in to this in more detail which you might find useful.

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