The Kyma Language for Sound Design, Version 4.5

The training sequence is just an Array of Arrays, each subarray containing two numbers — nothing specifically
musical yet:
chain :=
MarkovChain
trainingSequence: #(
#(0 4) #(3 2) #(-5 2) #(2 4) #(3 2) #(-5 2) #(2 4)
#(3 2) #(-5 4) #(2 2) #(3 2) #(-5 4) #(2 2) #(-5 2)
#(5 2) #(-7 4) #(1 2) #(-2 2) #(1 4) #(0 0.5) #(12 4)
)
chainLength: 2.
Next, there is a loop in which the index, i, takes on the values from 1 to 10. Each time through the loop a
new sequence is generated, using a different seed each time, and saved in the variable called seq:
1 to: 10 do: [ :i |
seq := chain newSequenceOfLength: 100 seed: i * 26.
In Smalltalk, you can also create a loop by sending the do: message to an Array. The following is a loop
in which the variable offDur takes on each of the values stored in the Array called seq. Each value in
seq is a subarray containing two numbers. Take a look through this code to see if every step makes sense
to you. (If not, don’t worry, it is all explained in more verbose style in the following paragraph!)
seq do: [ :offDur |
dur := (offDur at: 2) / i.
pitchOffset := offDur at: 1.
self
keyDownAt: t beats
duration: dur beats
frequency: 1 g + pitchOffset nn + i nn
velocity: i/10.
t := t + dur].
Each time through the loop, the second element of offDur is divided by i (the index of the outer loop)
and stored in dur. The first element of offDur is stored in the variable pitchOffset. Then a MIDI
event is created that starts on beat t, lasts for dur beats, and whose frequency is 1 g plus the number of
half steps stored in pitchOffset plus a number of half steps equal to the index i. Then the time counter
t is incremented by the duration of the event just created and the loop repeats. The overall effect is that
we hear several, related sequences, each one faster and at a higher pitch than the one before it.
Using MIDI Files with the MarkovChain
The longer the training sequence, the more likely the generated sequences are to sound related to the
original without being exact copies of the original. But entering long arrays by hand can be tedious, so
here is a little trick for obtaining long sequences of MIDI events for use in a MarkovChain: Create a
TimedEventSequence by reading it from a MIDI file, make sure it is monophonic, and then create a
MarkovChain using just the events from the TimedEventSequence, ignoring the starting beats.
Play fantasia bill and continue reading while it churns away on this long sequence of MIDI events. Here
is the script:
| pat chain seq |
pat :=
TimedEventCollection
timesAndEventsFromMIDIFile: 'DESAFIN1.MID'
channel: 3.
pat := pat asMonophonicEventSequence.
chain := MarkovChain trainingSequence: pat events chainLength: 3.
seq := chain newSequenceOfLength: 200 seed: 3.
(EventSequence events: seq) playOnVoice: self onBeat: 0 bpm: 90.
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