sandstorm

x.rb

require 'tempfile'

module Music
  refine Float do
    def hz
      self
    end

    def khz
      self * 1000
    end

    def second
      self
    end

    def seconds
      self
    end

    def beat
      self
    end
  end

  using Music

  SAMPLE_RATE = 48.0.khz
  PITCH_STANDARD = 440.0.hz
  TWELFTH_ROOT_OF_TWO = 2 ** ( 1.0 / 12 )
  BEATS_PER_MINUTE = 120

  def self.semitone(n = 0)
    PITCH_STANDARD * TWELFTH_ROOT_OF_TWO ** n
  end

  A4 = 0
  A4_SHARP = 1
  B4 = 2
  C5 = 3
  C5_SHARP = 4
  D5 = 5
  D5_SHARP = 6
  E5 = 7
  F5 = 8
  F5_SHARP = 9
  G5 = 10
  G5_SHARP = 11

  class Note
    def initialize(pitch: 440.0.hz, volume: 0.5, duration: 1.0.beat,
                   attack: 0.2, decay: 0.2, release: 0.2)
      @pitch = pitch
      @volume = volume
      @duration = duration
      @step = (@pitch * 2 * Math::PI) / SAMPLE_RATE
      @attack = attack
      @decay = decay
      @release = release
      @adsr_sustain = 0.2
    end


    def time
      60.0.seconds / BEATS_PER_MINUTE * @duration
    end

    def data
      (0..samples).map do |e|
        beat_control(e) * @volume * Math.sin(e * @step)
      end
    end

    def to_bytestring
      data.pack('e*')
    end

    private

    # /`--.
    # ads r
    def beat_control(ix)
      where = ix / samples
      case
      when where < @attack then where / @attack
      when where < (@attack + @decay) then 1.0 - (where - @attack) * (1.0-@adsr_sustain) / @decay
      when where < 1 - @release then @adsr_sustain # sustain
      else (1.0 - @release - where) * @adsr_sustain / @release + @adsr_sustain
      end
    end

    def samples
      SAMPLE_RATE * time
    end
  end

  NOTES = 12.times.map do |ix|
    Note.new(pitch: semitone(ix), duration: 1.0.beat).freeze
  end

  NOTES_HALF = 12.times.map do |ix|
    Note.new(pitch: semitone(ix), duration: 0.5.beat).freeze
  end

  NOTES_QUARTER = 12.times.map do |ix|
    Note.new(pitch: semitone(ix), duration: 0.25.beat).freeze
  end


  class Wave
    def initialize(*notes)
      @notes = notes
    end

    def play
      with_tempfile do |io|
        io.write(to_bytestring)
        io.close
        system("ffplay -showmode 1 -f f32le -ar #{SAMPLE_RATE} #{io.path}")
      end
    end

    private

    def with_tempfile
      io = Tempfile.new(__FILE__)
      yield(io)
    ensure
      io.close
      io.unlink
    end

    def to_bytestring
      @notes.map(&:to_bytestring).join
    end
  end

  MUSIC = Wave.new(
    *4.times.map { NOTES_QUARTER[A4] },
    NOTES_HALF[A4],
    *6.times.map { NOTES_QUARTER[A4] },
    NOTES_HALF[A4],

    *6.times.map { NOTES_QUARTER[D5] },
    NOTES_HALF[D5],

    *6.times.map { NOTES_QUARTER[C5] },
    NOTES_HALF[C5],

    Note.new(pitch: semitone(-2), duration: 0.5.beat),

    *4.times.map { NOTES_QUARTER[A4] },
    NOTES_HALF[A4]
  )
end