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Commission Music
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Wednesday, 7 April 2004

Explination of how pitches are picked for avant-happy song

Why? Because it's homework

There exists an overtone array: [ 2, 5, 3, 7, 9, 11, 13, 15, 17, 19, 21, 23]

notes can be constructed from this array as overtones:

2/2 5/4 3/2 7/4 9/8 11/8 13/8 15/8 17/16 19/16/ 21/16 23/16

or the inversions:

2/2 8/5 4/3 16/9 16/11 16/13 16/15 32/17 32/19 32/21 32/23

the three notes played are always adjacent to each other, for example:

17/16, 19/16, 21/16

Melodies are formed by taking a triad, picking one of the ratios to be a pivot, inverting it and then picking adjacent ratios. For example, if we pick 19/16 as the pivot from the above triad, we would invert it to get 32/19. We then pick adjacent ratios. We can take the two ratios above the pivot, the two below the pivot or one on either side. 23 wraps around back to 2 in case we go off the edge of the array. So we could pick

32/19 32/21 32/23

as out next set of triads. then we would pick a pivot from that array, invert and pick adjacent ratios.

Each set of rhythmic patterns for the marimba sound goes through this process and saves the result in an array, so the marimba plays the same triads every time it plays a particular pattern.

The pivot ratio is played a bit louder than the other two. It is also sent to a sustained baseline tone. The adjacent frequencies played by the marimba and are put into another array for the counter-melody.

The counter-melody gets it's pitches from the array created by the marimba routine. It treats this as a FILO queue. It does not play when the marimba is playing or if it's current rhythmic pattern calls for a rest. The length of the note played is the length last used by the marimba.

Some patterns, especially in the first and third section, add more notes to the FILO queue than they leave space for the counter-melody to play them. the patterns in the middle section have a lot of space (and long durations) and the FILO queue may empty by the end of the section.

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