ryohey/functional-music-programming

Functional Music Programming

Functional & Type-safe Programming for music

Types

• Pitch is the object to represent the pitch
• Duration is the object to represent the duration
• Time is the object to represent the point in time
• Period is Time & Duration
• Note is Pitch & Period
• Rhythm is Period[]

Functions

• Scale = (index: ScaleIndex) => Pitch
• Transformer<T> = <S extends T>(notes: S[]) => S[]

Transformers

General

• compose makes the composite function
• duplicate copies the list elements applied transform

Time

• move(time) returns the function that adds the time to Time objects
• repeat(time) returns the function that creates copies of Time objects moved by time
• loop(count, time) returns the function that creates copies of Time objects for the loop count
• template(pattern) returns the function that creates copies of Time objects by the array of timings.
• stroke(offset) returns the function that moves notes like a guitar
• rhythm(pattern, unitTime, noteChar) returns the function to create a notes from the drum pattern string

Pitch

• transpose(pitch) returns the function that adds the pitch to Pitch objects

Period

• legato returns the function that modifies durations to make notes legato

Defined scales

• major(root)
• naturalMinor(root)
• harmonicMinor(root)
• majorPentatonic(root)
• minorPentatonic(root)
• melodicMinor(root)
• dorianMode(root)
• mixolydianMode(root)
• minorPentatonicBlues(root)
• majorPentatonicBlues(root)
• triad(root)

Song writing example

Drum

const n4th = 1
const n8th = n4th / 2

const kick = {
  pitch: 36,
  duration: 1,
  time: 0
}

const snare = {
  pitch: 38,
  duration: 1,
  time: 0
}

const hihat_close = {
  pitch: 42,
  duration: 1,
  time: 0
}

const drums = loop(4, 8)(_.concat(
  rhythm("x _ xx_ x _x x_", n8th)([kick]), 
  rhythm("_ x __x _ x_ _x", n8th)([snare]), 
  loop(8, 1)([hihat_close])
))

Chords

const scale = majorPentatonic(38)

const piano = compose<Note>(
  loop(2, 8),
  transpose(12),
)(_.concat(
  move(0)(triad(0)(scale).map(pitchToNote)),
  move(2)(triad(1)(scale).map(pitchToNote)),
))

Melody

const melody = compose(
  transpose(24),
  loop(2, 8),
  legato(),
  stroke(1),
)([0, -1, 0, 1, 2, 4, -1, 0].map(i => scale(i)).map(pitchToNote))

Audio Processing

• Render the audio with WebAudio API
• Play songs with the SoundFont
• Support the offline rendering

Effects

Higher Order Function for applying effects to the AudioNode

• mix(amount) mixes two AudioNodes
• gain(gainValue) gains volume
• delay adds the delay effect
• reverb adds the reverb effect