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require 'v1/instruments'
transport and parts should be pasted in from
masterGain can be used to prevent clipping
instrumentBuilders is a hash of track labels (the object keys in the `parts` hash) to functions that take a note and returns a function to be passed to @play()
parseMidi = (options={}) ->
transport = options.transport
parts =
instrumentBuilders = options.instrumentBuilders || {}
masterGain = options.masterGain || -20
throw new Error "Options must specify 'parts' values for parseMidi."
# Tone.js uses a default "parts per quarter" of 48
# BPM is specified in the transport
if options.transport?
@setBPM parseInt(transport.bpm) * 48
@setMasterGain masterGain
processedNotes = []
for trackName, track of parts
for noteData in track
processedNotes.push {
instrument: trackName
start: parseInt(noteData.time).beats()
duration: parseInt(noteData.duration).beats()
velocity: parseFloat(noteData.velocity)
frequency: Frequency.noteNumber(noteData.midiNote)
for note in processedNotes
# Closures in a loop are tricky, but CoffeeScript provides the do keyword
# which will push a new lexical scope to capture outside variables.
# We *also* must bind to this, by using => intstead of ->, to ensure the
# `do` closure is run in the scope provided by `buildTrack`.
do (note) =>
@after note.start, ->
if builder = instrumentBuilders[note.instrument]
@play builder(note)
# Be slightly more careful about the shared namespace when this is
# apply'd to run in buildTrack().
_o = new Oscillator(frequency: note.frequency, type: Oscillator.SQUARE)
_e = new Envelope(decayTime: note.duration)
@play _e.process(_o)