OpenMusic Tutorials

Prev| Chapter 9. Playing MIDI II| Next

Tutorial 29: Working with MIDI files II

Channel parsing

Topics

Converting a standard Midifile into a Chord-seq with correct microintervals.

Key Modules Used

Midifile , omloop, omif, repeat-n

The Concept:

Most commercial MIDI sequencers don’t support microintervals. When working with these environnments, one must use a multichannel setup in order to simulate microintervals, by “pitchbending” certain channels as is done automatically in Openmusic. In this tutorial we will show how to convert one of these MIDI files into a Chord-seq which will play correct microintervals.

The Patch:

In our example we have created a simple multitrack MIDIfile. It represents a chromatical segment of a quarter-tone scale starting from C3. The first MIDI track is on channel 1 which is the normally tuned track; The second is on the channel 2, which shouold be tuned 1 quartertone higher. We need to get these notes back onto a single channel and adjust their midics to reflect the detuning of the other channels in the MIDI file.

At (A) the MIDIfile is opened (or dragged into an OpenMusic patch).

Each color represents a different MIDI channel. (Here blue is channel 1 and green is channel 2)

Now if we open the Chord-seq (B) editor and check the chan popup menu, we can see each note’s channel.

In the first omloop (C) we will use omif to ‘correct’ each note, and turn it into the right pitch, by checking to see whether the channel equals 2. Note that we use two listloop boxes to enumerate the MIDI notes and the channel assignments simultaneously.

In this case our line is of single notes. If there had been chords we would have needed to process the onset times and assign the same onset time to every note of the chord. This is done with the omloop below:

The _ldur_ output is a list of lists. Each integer is a duration of a single note, so all we have to do is flatten the list using flat.

All this results in the following:

Each note is correctly parsed to the right channel according to its tuning.

OpenMusic