Problems with the design of a MIDI editor

Mixing MIDI files

My MIDI editor HUMidi offers a feature that allows mixing two MIDI files. You may have experienced that this feature does not always produce the expected results.

MIDI ist not the best base to start a mix process. The follwing questions must be answered (this is not a complete list of the problems):

Can we mix MIDI files with different tempi (Adagio file with an Allegro file)?
What to do with different tonalities (C major with Bb minor)?
What to do with different measures (3/4 with 6/8)?
What to do with anacrusis?

Some of theses questions can be answered in a rather brutal way:

Different tonalities: MIDI has no mandatory tonality information. So don't care for tonality
Different tempi: MIDI has no mandatory tempo information. So don't care for tempo.
Different measures: MIDI has no mandatory measure information. So don't care for measure information.

In fact things are not so simple: instead of not taking are of information like tempo, tonality, measure I prefer to produce first two clean versions of the files - i.e. to wipe out all tempo, measure, tonality information and then to mix the files. As the mixing process can not decide which of these information should dominate I leave it to the user to reintroduce these information into the mix result.

There couldbe a special case when tonality, tempo and measure information could be preserved: when both files are exactly identical in these parameters. HUMidi at the moment has no solution for this special case.

The analogy with mixing "normal" audio files should be noticed: a mxing process for audio files does not take care of tempo, tonality or measure information simply because audio files (WAVE, MP3 etc.) do not have these information.

When you mix MIDI files you may however encounter additional problems:

MIDI files may have different time bases (in MIDI called "division"). It is thus necessary to normalize the time bases before you mix the files.
MIDI has no bar information. When you say "mix in file two after bar 5 / beat 3" then you use information that you (the human user) have but that is lacking in a MIDI file. Bar/beat information must be reconstructed in MIDI files - this process can produce errors (see my short article on the anacrusis problem)
MIDI has relative (not absolute) time information for the note events. As the mixing process may introduce new notes in the sequence of the the existing notes you must modify the time information for the events. This may lead to unexpected results.
When you mix two large MIDI files then the resulting mixed file may show too many tracks. I prefer therefor to mix rather channels than tracks (channels and tracks are not the same!), i.e. if the first file has events in channel 5 and the second file also then all events extracted from both files for channel 5 are combined in the mix file on channel 5 - no additional track is created.

Kontakt / Contact

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