The idea is to have one channel for each scale degree. Then you apply an appropriate pitch bend for the channel at the start of the piece. Then send each note on the appropriate channel - note 60 on channel 1, note 61 on channel 2 and so on.

To work out the pitch bend numbers from the cents values, use the data that 100 cents = 4096 midi pitch bend units.

For multitimbral monophonic midi, another method is useful - you can keep all the notes in their original channels as only one pitch bend is requred at a time, and apply appropriate pitch bends to all the notes as you play them - you may need a new pitch bend before nearly every note..

This is easy to program and can also be done by hand easily too.

For other scales with other numbers of notes to an octave, or non octave scales, or ones that have close clusters of notes, e.g. less than a quarter tone apart, you may need to use a midi keyboard mapping that sends several midi in notes to the same midi out note, varying the pitch bends only - if so you need to change the note numbers too before sending them on.

Choose the nearest midi note number to the desired pitch - and figure the pitch bend needed from the note number and desired pitch.

For muli-timbral polyphonic music, it's more complex - but it can be done as that's what FTS does. So it could be done by hand too, by going through the midi file on a note by note basis. The basic idea here is to change the ptich bends as seldom as possible, so if possible play a note on a channel that already has the appropriate pitch bend. If that's not possible, choose a channel that has no notes in play, and with the most recent note off as long ago as possible (because notes often continue to sound for a short while in a resonance / reverb effect after you switch them off). Change the pitch bend for that one.

Modern GM capable sound cards happily will let one play on several different instruments in the same channel at once - so long as they play separate note numbers. This makes the multi-timbral polyphonic midi much easier to retune - just use the same method as one uses for mono-timbral midi, and send any program changes before the notes you send as needed (you could send them before every note, or better, keep track of the most recent one for each channel and only send them when the instrument needed changes). Midi clips made this way may not work as intended on synthesizers or soft synths, as they may be designed to work with a single instrument at a time in each channel.

You can also do multi-timbral polyphony with varied effects such as modulation, tremulo etc. for eah part - that gets more complex again, but of course it too could be done by hand. Same idea - but you have to make sure that each note gets played in a channel with all the appropriate effects as well as the desired pitch bend. If none is available, then change the effects for a channel with no notes in play any more (if available - otherwise you get to the point where you may have to switch notes off because of the amount of pitch polyphony + effects needed).

This site goes into the basics of the method of adding pitch bends by hand (with some clips done by hand). Wauchope's Allotonal* General MIDI Files

So as you see it can all be done by hand, and for some midi files it is reasonably easy to do; indeed this used to be the only way it could be done. However composers find that use of a retuning program helps for most midi clips. You need to spend less time thinking about how to achieve the tuning, and can devote your time to the actual composition itself instead.

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What to do next

Freeware / Shareware status: This feature is shareware. You need the Midi Relaying (Midi In) unlock key - or if you want to use the Rhythms and Polyrhythms metronome, or work with the fractal tunes you need the Complete level.

To continue reading about use of Tune Smithy as a composition tool, go on to Links.

To find this feature after you download Tune Smithy:
Look in the Tune Smithy Tasks window for: Composition Retuning