A programming language for generative music composition using cellular automata
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A simple programming language for generative music composition using cellular automata

The language

Parts and rules

A Celltone program is made up of two things: a number of parts and a number of rules. A part is a named list of notes and pauses, for example:

p = [0, _, _, 4, _, _, 7, _, _]

Notes are numbers and pauses are underscores. The number 0 represents a C, 4 is an E, and so on.

Rules are used to transform the parts. Example:

{p[0] == 0, p[1] == _} => {p[0] = _, p[1] = 2}

This example rule would transform the part we defined earlier into

p = [_, 2, _, 4, _, _, 7, _, _]

Iterations and cyclicity

Rules are applied to parts in an iterative fashion. The length of an iteration is by default the length of the longest part. After each iteration the parts are updated based on the rule set. Parts can be of different lengths, and they are played back in a cycle.

For example, say we have the parts

a = [0, _, 2, _]
b = [4, _, _]

During iteration 1, a would play [0, _, 2, _], and b would play [4, _, _, 4]. During iteration 2, a would play [0, _, 2, _], but b would play [_, _, 4, _].

Rules in detail

The cyclicity of the parts also applies to the rules. Say we have the parts from above, along with the rule

{a[0] != _, b[0] != _} => {b[-1] = 7}

After the first iteration, the rule would match the first beat, and the parts would now be

a = [0, _, 2, _]
b = [4, _, 7]

For the second iteration, b is shifted by one step, and the notes played are now

[0, _, 2, _] # a
[_, 7, 4, _] # b

Rules are evaluated in the order they are defined in the source file. Notes can match in the left hand side of many rules, but may only be altered by the right hand side in one rule. For example, if we have

p = [0, _, 2, 4]
{p[0] == 2, p[1] != _} => {p[0] = _} # rule 1
{p[0] == _} => {p[0] = 2, p[1] = 7}  # rule 2

both rules would match, but only rule 1 would get applied. This is because the note at position 3 would have been modified by the second rule, but it had already been modified by the first rule.

Indexed parts

Not only can notes be indexed using the x[+2] syntax, parts can also be indexed using the following syntax:

{<0>[0] == <1>[0], <0>[1] != _} => {<0>[0] = 1, <1>[1] = _}

For the index to have meaning, parts need to be ordered. By default parts are ordered in the order they are defined, but the global propoerty <partorder> can be used to specify explicit ordering:

<partorder> = [a, c, b, d]

Part properties

Parts have properties that can be set (but currently not changed) in the source file. At the moment, channel, velocity, octava and transpose are supported. Example:

a = [0, _, 4, _, 9]
a.channel = 4
a.velocity = 90
a.octava = 5

Global properties

Global properties affect the piece as a whole. Currently the available properties are <tempo>, <iterlength>, <subdiv>, <transpose> and <partorder>. Example:

<tempo> = 124
<subdiv> = 16


Comments start with # and end at the end of the line.


Installation is pretty straight forward -- at least once you have pyPortMidi installed.

First, make sure you have the python, python-setuptools and portmidi packages. On Linux you also need the ALSA development packages. Then, download pyPortMidi. I use aalex's fork on BitBucket: https://bitbucket.org/aalex/pyportmidi/downloads/python-portmidi-0.0.7.tar.gz In the python-portmidi directory, run sudo python setup.py install. If this fails, it should hint at what went wrong. Maybe you need to run sudo easy_install pyrex? There's good documentation at https://bitbucket.org/aalex/pyportmidi/wiki/Home on how to get pyPortMidi working.

When that is done, download the Celltone sources, cd into the Celltone directory, and run sudo python setup.py install.

Running Celltone

Once installed, run Celltone by giving it a filename as an argument

celltone examples/bubblesort.ct

To see the available command line options, type

celltone -h

Debug output

To enable debug output, add -v, -vv or -vvv as an argument. -v will output the current parts and their notes, -vv will additionally output the rules that were used in this generation, and -vvv will also indicate which notes were used in the application of the rule.

MIDI output

By default, output is fed to the default MIDI device in realtime, using PortMidi. Use a tool like pmdefaults or qjackctl to route the MIDI output to some MIDI input device.

You can also use Celltone to generate MIDI files offline using the --file command line flag.

Runtime source file updates

Celltone can be used as a performance tool, by specifying the --update command line flag. This allows you to update the source file in realtime, during playback.