Process Music with music21

Last July, I was watching this gorgeous video showing the waves created by a set of pendulums of different (but simple ratio) lengths after they're simultaneously released:

(courtesy Harvard Science Center demonstrations)

I thought about ways that such a demonstration could be made musically using simple processes.  After writing the music21 code to do so, I discovered that several other composers have done similar things, so I don't think that it's absolutely original, but I wanted to share the possibilities.  First the opening of the score and the recording:

Play here directly: Or if that doesn't work: Click here
Here's the music21 code used to make it (unhighlighted code in music21-tools Github repository under composition.phasing):

1. def pendulumMusic(show = True,
2.                   loopLength = 160.0,
3.                   totalLoops = 1,
4.                   maxNotesPerLoop = 40,
5.                   totalParts = 16,
6.                   scaleStepSize = 3,
7.                   scaleType = scale.OctatonicScale,
8.                   startingPitch = 'C1'
9.                   ):
10.     from music21 import scale, pitch, stream, note, chord, clef, tempo, duration, metadata
11.    
12.     totalLoops = totalLoops * 1.01
13.     jMax = loopLength * totalLoops
14.    
15.    
16.     p = pitch.Pitch(startingPitch)
17.     if isinstance(scaleType, scale.Scale):
18.         octo = scaleType
19.     else:
20.         octo = scaleType(p)
21.     s = stream.Score()
22.     s.metadata = metadata.Metadata()
23.     s.metadata.title = 'Pendulum Waves'
24.     s.metadata.composer = 'inspired by http://www.youtube.com/watch?v=yVkdfJ9PkRQ'
25.     parts = [stream.Part(), stream.Part(), stream.Part(), stream.Part()]
26.     parts[0].insert(0, clef.Treble8vaClef())
27.     parts[1].insert(0, clef.TrebleClef())
28.     parts[2].insert(0, clef.BassClef())
29.     parts[3].insert(0, clef.Bass8vbClef())
30.     for i in range(totalParts):
31.         j = 1.0
32.         while j < (jMax+1.0):
33.             ps = p.ps
34.             if ps > 84:
35.                 active = 0
36.             elif ps >= 60:
37.                 active = 1
38.             elif ps >= 36:
39.                 active = 2
40.             elif ps < 36:
41.                 active = 3
42.            
43.             jQuant = round(j*8)/8.0
45.             establishedChords = parts[active].getElementsByOffset(jQuant)
46.             if len(establishedChords) == 0:
47.                 c = chord.Chord([p])
48.                 c.duration.type = '32nd'
49.                 parts[active].insert(jQuant, c)
50.             else:
51.                 c = establishedChords[0]
52.                 pitches = c.pitches
53.                 pitches.append(p)
54.                 c.pitches = pitches
55.             j += loopLength/(maxNotesPerLoop - totalParts + i)
56.             #j += (8+(8-i))/8.0
57.         p = octo.next(p, stepSize = scaleStepSize)
58.            
60.     parts[0].insert(0, tempo.MetronomeMark(number = 120, referent = duration.Duration(2.0)))
61.     for i in range(4):
62.         parts[i].insert(int((jMax + 4.0)/4)*4, note.Rest(quarterLength=4.0))
63.         parts[i].makeRests(fillGaps=True, inPlace=True)
64.         parts[i] = parts[i].makeNotation()
65.         s.insert(0, parts[i])
66.    
67.     if show == True:
68.         #s.show('text')
69.         s.show('midi')
70.         s.show()

One nice thing that you can do is call pendulumMusic with different attributes, such as:

        pendulumMusic(show = True, 
                  loopLength = 210.0, 
                  totalLoops = 1, 
                  maxNotesPerLoop = 70,
                  totalParts = 64,
                  scaleStepSize = 1,
                  scaleType = scale.ChromaticScale,
                  startingPitch = 'C1',
                  )

Play here directly: Or if that doesn't work: Click here

which gives a denser score that has parts that sound like Nancarrow. Or this version...:

        pendulumMusic(show = True, 
                  loopLength = 210.0, 
                  totalLoops = 1, 
                  maxNotesPerLoop = 70,
                  totalParts = 12,
                  scaleStepSize = 5,
                  scaleType = scale.ScalaScale('C3', '13-19.scl'),
                  startingPitch = 'C2',
                  )

Play here directly: or if that doesn't work: Click here which should produce a 19-tone version of the same piece.

Happy process music composing!

(Updated 2021 September to replace Flash links from 2012 with HTML 5 and point to the correct Github repository)