303 lines
8.7 KiB
Markdown
303 lines
8.7 KiB
Markdown
---
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abstract: Programming sound in Live-Sequencer and ChucK
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lastupdated: 2013
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---
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# Sound Programming
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*2013.*
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Much can be programmed, and that includes sound. In the digital world,
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sound is typically represented by sequences of about 90 kB per second,
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so "printing" sound is merely a matter of printing bytes. As such, any
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general purpose language can be used to generate sounds.
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However, it's boring to create a program that does nothing but print
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bytes, and it's potentially difficult to make those bytes sound nice; we
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want abstractions to simplify matters for us: instruments, drums,
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musical notes, and a high-level program structure. Many programming
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languages have good libraries that allow us to achieve just that, but to
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keep it simple we'll focus on how to program sound in two languages
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designed to output sound: ChucK and Live-Sequencer.
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Let's create some sounds.
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The square wave
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===============
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We'll start with ChucK and a small square wave program:
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``` {.c}
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// Connect a square oscillator to the sound card.
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SqrOsc s => dac;
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// Set its frequency to 440 Hz.
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440 => s.freq;
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// Lower the volume.
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0.1 => s.gain;
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// Let it run indefinitely.
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while (true) {
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1000::second => now;
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}
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```
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ChucK is an imperative language. Instructions on how to install and run
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it can be found on its [website](http://chuck.cs.princeton.edu/), along
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with other useful information. You can listen to the above sound
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[here](square.flac).
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To do the same in Live-Sequencer, we must find a square wave
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"instrument" and use that.
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``` {.haskell}
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module SquareWave where
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-- Basic imports.
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import Prelude
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import List
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import Midi
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import Instrument
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import Pitch
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-- The function "main" is run when the program is run.
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-- It returns a list of MIDI actions.
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main = concat [ program lead1Square -- Use a square wave instrument.
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, cycle ( -- Keep playing the following forever.
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note 1000000 (a 4) -- Play 1000000 milliseconds of the musical note A4
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) -- about 440 Hz.
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]; -- End with a semicolon.
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```
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Live-Sequencer differs from ChucK in that it is functional, but another
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major difference is that while ChucK (in general) generates raw sound
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bytes, Live-Sequencer generates so-called MIDI codes, which another
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program converts to the actual audio. Live-Sequencer has a couple of
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funky features such as highlighting which part of one's program is
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played; read about it and how to install and run it at [this
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wiki](http://www.haskell.org/haskellwiki/Live-Sequencer). You can listen
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to the above sound [here](squarewave.flac).
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Something more advanced
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=======================
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Let's try to create a small piece of music which can be expressed easily
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in Live-Sequencer (listen [here](melodyexample.flac)):
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``` {.haskell}
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module MelodyExample where
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import Prelude
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import List
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import Midi
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import Instrument
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import Pitch
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-- Durations (in milliseconds).
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en = 100;
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qn = 2 * en;
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hn = 2 * qn;
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wn = 2 * hn;
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twice x = concat [x, x];
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main = cycle rpgMusic;
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rpgMusic = concat [ partA g
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, [Wait hn]
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, twice (partB [b, d])
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, partB [a, c]
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, partA b
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];
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partA t = concat [ program frenchHorn
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, mel2 c e 4
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, mel2 c e 5 -- The '=:=' operator merges two lists of actions
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=:= -- so that they begin simultaneously.
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(concat [ [Wait wn]
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, mel2 d t 3
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])
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];
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partB firsts = concat [ program trumpet
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, concat (map mel0 [c, e])
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=:=
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mergeMany (map mel1 firsts)
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];
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-- Instrument-independent melodies.
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mel0 x = concat [ note wn (x 3)
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, note hn (x 4)
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, note en (x 2)
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, [Wait wn]
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, twice (note qn (x 2))
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];
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mel1 x = concat [ note (wn + hn) (x 5)
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, note (hn + qn) (x 4)
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];
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mel2 x y n = concat [ twice (note qn (x 3))
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, concatMap (note hn . y) [3, 4, 4]
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, note wn (x n) =:= note wn (y n)
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];
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```
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When you play the program from the Live-Sequencer GUI, the code in use
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is highlighted:
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{width=700}
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The same could be expressed in ChucK, but the comparison wouldn't be
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fair. While Live-Sequencer is designed for describing melodies, ChucK's
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purpose is sound synthesis, which is more general. We'll create
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something more fitting of ChucK's capabilities, while still focusing on
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the use of instruments (listen [here](more_advanced.flac)):
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``` {.c}
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// Background music for an old sci-fi horror B movie.
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// Filters.
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Gain g;
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NRev reverb;
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// Connect the Gain to the sound card.
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g => dac;
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// Connect the data sent to the sound card through the reverb filter back to the
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// sound card.
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adc => reverb => dac;
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// Instruments.
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Mandolin mandolin;
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0.2 => mandolin.gain;
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Sitar sitar;
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0.8 => sitar.gain;
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Moog moog;
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// Instrument connections to the Gain.
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mandolin => g;
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sitar => g;
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moog => reverb => g;
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// Play a frequency 'freq' for duration 'dura' on instrument 'inst'.
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fun void playFreq(StkInstrument inst, dur dura, int freq) {
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freq => inst.freq; // Set the frequency.
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0.1 => inst.noteOn; // Start playing with a velocity of 0.1.
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dura => now;
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0.1 => inst.noteOff; // Stop playing.
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}
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// Play a melody.
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fun void a_melody(StkInstrument inst, int freq_offset) {
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int i;
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// Fork the command to play "in the background".
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spork ~ playFreq(moog, 600::ms, 400 - freq_offset);
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for (0 => i; i < 3; i++) {
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playFreq(inst, 200::ms, 220 + freq_offset + 10 * i);
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}
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// Create an array and use every element in it.
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[3, 4, 4, 5, 3] @=> int ns[];
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for (0 => i; i < ns.cap(); i++)
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{
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playFreq(inst, 100::ms, ns[i] * 132 + freq_offset);
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}
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}
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// Infinite sound loop of pseudo-random frequencies.
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while (true) {
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spork ~ a_melody(moog, Math.random2(0, 30));
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Math.random2f(0.4, 0.9) => g.gain; // Adjust the gain.
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a_melody(mandolin, Math.random2(0, 350));
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a_melody(sitar, Math.random2(200, 360));
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}
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```
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Algorithmic composition
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=======================
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Why not have the computer generate the melody as well as the sound? That
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**sounds** like a great idea!
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Enter [L-systems](https: / / en.wikipedia.org / wiki / L-system). An
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L-system has an alphabet and a set of rules, where each rule is used to
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transform the symbol on the left-hand side to the sequence of symbols on
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the right-hand side. We'll use this L-system to generate music:
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``` {.c}
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-- Based on https://en.wikipedia.org/wiki/L-system#Example_7:_Fractal_plant
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Alphabet: X, F, A, B, P, M
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Rules:
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X -> FMAAXBPXBPFAPFXBMX
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F -> FF
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```
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If we evaluate a L-system on a list, the system's rules are applied to
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each element in the list, and results are concatenated to make a new
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list. If we assign each symbol to a sequence of sounds and run the
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L-system a few times, we get [this](lsystem.flac).
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``` {.haskell}
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module LSystem where
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import Prelude
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import List
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import Midi
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import Instrument
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import Pitch
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en = 100;
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qn = 2 * en;
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hn = 2 * qn;
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wn = 2 * hn;
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-- Define the L-System.
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data Alphabet = X | F | A | B | P | M;
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expand X = [F, M, A, A, X, B, P, X, B, P, F, A, P, F, X, B, M, X];
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expand F = [F, F];
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expand _ = [];
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-- Map different instruments to different channels.
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channelInsts = concat [ channel 0 (program celesta)
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, channel 1 (program ocarina)
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, channel 2 (program sitar)
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];
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-- Define the mappings between alphabet and audio.
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interpret X = [Wait hn];
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interpret F = channel 0 (note qn (c 4));
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interpret A = channel 1 (note qn (a 5));
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interpret B = channel 1 (note qn (f 5));
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interpret P = channel 2 (note hn (a 3));
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interpret M = channel 2 (note hn (f 3));
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-- A lazily evaluated list of all iterations.
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runLSystem expand xs = xs : runLSystem expand (concatMap expand xs);
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-- The sound from a L-System.
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getLSystemSound expand interpret iterations start
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= concatMap interpret (runLSystem expand start !! iterations);
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-- Use the third iteration of the L-System, and start with just X.
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main = channelInsts ++ getLSystemSound expand interpret 3 [X];
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```
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Using an L-system is one of many ways to take composition to a high
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level. L-systems can be used to generate fractals, which are nice.
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And so on
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=========
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Many abstractions in sound generation allow for fun sounds to happen.
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Interested people might want to also take a look at e.g.
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[Euterpea](http://haskell.cs.yale.edu/euterpea-2/), [Pure
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Data](http://puredata.info/), or [Csound](http://csounds.com/).
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Originally published
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[here](http://dikutal.metanohi.name/artikler/sound-programming).
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