A simple sequencer for the HTML5 Audio API. Notes, rests, and durations only with configurable tempo.

chromatic_scale.coffee

# Full chromatic scale with frequencies

chromatic_scale =
  "C0" :  16.35
  "C#0":  17.32
  "Db0":  17.32
  "D0" :  18.35
  "D#0":  19.45
  "Eb0":  19.45
  "E0" :  20.60
  "F0" :  21.83
  "F#0":  23.12
  "Gb0":  23.12
  "G0" :  24.50
  "G#0":  25.96
  "Ab0":  25.96
  "A0" :  27.50
  "A#0":  29.14
  "Bb0":  29.14
  "B0" :  30.87
  "C1" :  32.70
  "C#1":  34.65
  "Db1":  34.65
  "D1" :  36.71
  "D#1":  38.89
  "Eb1":  38.89
  "E1" :  41.20
  "F1" :  43.65
  "F#1":  46.25
  "Gb1":  46.25
  "G1" :  49.00
  "G#1":  51.91
  "Ab1":  51.91
  "A1" :  55.00
  "A#1":  58.27
  "Bb1":  58.27
  "B1" :  61.74
  "C2" :  65.41
  "C#2":  69.30
  "Db2":  69.30
  "D2" :  73.42
  "D#2":  77.78
  "Eb2":  77.78
  "E2" :  82.41
  "F2" :  87.31
  "F#2":  92.50
  "Gb2":  92.50
  "G2" :  98.00
  "G#2":  103.83
  "Ab2":  103.83
  "A2" :  110.00
  "A#2":  116.54
  "Bb2":  116.54
  "B2" :  123.47
  "C3" :  130.81
  "C#3":  138.59
  "Db3":  138.59
  "D3" :  146.83
  "D#3":  155.56
  "Eb3":  155.56
  "E3" :  164.81
  "F3" :  174.61
  "F#3":  185.00
  "Gb3":  185.00
  "G3" :  196.00
  "G#3":  207.65
  "Ab3":  207.65
  "A3" :  220.00
  "A#3":  233.08
  "Bb3":  233.08
  "B3" :  246.94
  "C4" :   261.63
  "C#4":  277.18
  "Db4":  277.18
  "D4" :  293.66
  "D#4":  311.13
  "Eb4":  311.13
  "E4" :  329.63
  "F4" :  349.23
  "F#4":  369.99
  "Gb4":  369.99
  "G4" :  392.00
  "G#4":  415.30
  "Ab4":  415.30
  "A4" :  440.00
  "A#4":  466.16
  "Bb4":  466.16
  "B4" :  493.88
  "C5" :  523.25
  "C#5":  554.37
  "Db5":  554.37
  "D5" :  587.33
  "D#5":  622.25
  "Eb5":  622.25
  "E5" :  659.26
  "F5" :  698.46
  "F#5":  739.99
  "Gb5":  739.99
  "G5" :  783.99
  "G#5":  830.61
  "Ab5":  830.61
  "A5" :  880.00
  "A#5":  932.33
  "Bb5":  932.33
  "B5" :  987.77
  "C6" :  1046.50
  "C#6":  1108.73
  "Db6":  1108.73
  "D6" :  1174.66
  "D#6":  1244.51
  "Eb6":  1244.51
  "E6" :  1318.51
  "F6" :  1396.91
  "F#6":  1479.98
  "Gb6":  1479.98
  "G6" :  1567.98
  "G#6":  1661.22
  "Ab6":  1661.22
  "A6" :  1760.00
  "A#6":  1864.66
  "Bb6":  1864.66
  "B6" :  1975.53
  "C7" :  2093.00
  "C#7":  2217.46
  "Db7":  2217.46
  "D7" :  2349.32
  "D#7":  2489.02
  "Eb7":  2489.02
  "E7" :  2637.02
  "F7" :  2793.83
  "F#7":  2959.96
  "Gb7":  2959.96
  "G7" :  3135.96
  "G#7":  3322.44
  "Ab7":  3322.44
  "A7" :  3520.00
  "A#7":  3729.31
  "Bb7":  3729.31
  "B7" :  3951.07
  "C8" :  4186.01
  "C#8":  4434.92
  "Db8":  4434.92
  "D8" :  4698.64
  "D#8":  4978.03
  "Eb8":  4978.03

gistfile1.coffee

class Sequencer

  notes =
    # C Major Scale
    # Define whatever notes you want here.
    # Quick reference for equal-tempered:
    # http://www.phy.mtu.edu/~suits/notefreqs.html

    "C4": 261.63
    "D4": 293.66
    "E4": 329.63
    "F4": 349.23
    "G4": 392.00
    "A4": 440.00
    "B4": 493.88
    "rest": -1

  constructor: (options) ->
    @instrument    = options.instrument
    @tempo         = options.tempo or 120
    @sequence      = options.sequence or []
    @complete      = options.oncomplete

    @setupDurations()

  setupDurations: ->
    base      = 60000 / @tempo

    whole     = base * 4
    half      = base * 2
    quarter   = base
    eighth    = base / 2
    sixteenth = base / 4

    @durations =
      'whole'    : base
      'half'     : half
      'quarter'  : quarter
      'eighth'   : eighth
      'sixteenth': sixteenth


  start: ->
    if @sequence.length is 0
      throw "Sequencer needs some steps: e.g. [{note: 'G4', duration: 'quarter'}]"
    else
      i    = 0
      @playStep(i)

  playStep: (i) ->
    step = @sequence[i]
    @instrument.playNote notes[step.note], @durations[step.duration], =>
      i = i + 1
      if i == @sequence.length
        @completeCallback()
      else
        @playStep(i)

  completeCallback: ->
    if @complete
      @complete()

gistfile2.coffee

class Instrument
  constructor: (context, options) ->
    @context = context
    @type    = options.type

  createOsc: ->
    osc = @context.createOscillator()
    osc.type = @type or 0
    osc.connect(@context.destination)

    @polyfill(osc) unless osc.start

    return osc

  playNote: (freq, duration, callback) ->
    unless freq is -1
      @osc = @createOsc()
      @osc.frequency.value = freq or 440
      @osc.start(0)

    length = setTimeout =>
      @stop()
      callback()
      clearTimeout(length)
    , duration

  stop: ->
    if @osc
      @osc.stop(0)
      @osc.disconnect()

  polyfill: (osc) ->
    # Safari 6.0.5 uses outdated method names.
    # Chrome uses the most current ones. This
    # is a polyfill for Safari

    osc.start = (t) ->
      osc.noteOn(t)
    osc.stop  = (t) ->
      osc.noteOff(t)

gistfile3.coffee

sequence = [
  note: "C4", duration: "quarter"
,
  note: "G4", duration: 'half'
,
  note: "E4", duration: 'whole'
,
  note: "C4", duration: 'whole'
,
  note: "rest", duration: 'eighth'
,
  note: "E4", duration: 'eighth'
,
  note: "F4", duration: 'quarter'
,
  note: "E4", duration: 'quarter'
]


if "webkitAudioContext" of window
  stage = new webkitAudioContext()
  
  voice = new Instrument stage,
    type: 2 # square wave
  
  sequence = new Sequencer
    tempo: 120
    sequence: sequence
    instrument: voice
    oncomplete: ->
      alert 'sequence complete'
  sequence.start()

“albatrocity/chromatic_scale.coffee” refers to a file in a code repository (likely on GitHub) named chromatic_scale.coffee. Here’s what it means:

albatrocity → This is likely the username or organization that owns the repository.

chromatic_scale.coffee → This is a file written in CoffeeScript (hence the .coffee extension). Based on the name, the file probably contains code to generate or work with a chromatic scale (a musical scale that includes all 12 semitones in an octave).

So, the thread is pointing to or discussing a CoffeeScript implementation of a chromatic scale in a repository owned by the user albatrocity.

Regards: ff beta testing