Add basic envelope implementation

lib/music_theory.rb

@@ -13,6 +13,7 @@
 require "music_theory/output"
 require "music_theory/play"
 require "music_theory/pitch"
+require "music_theory/envelope"
 
 
 module MusicTheory

lib/music_theory/envelope.rb

@@ -1,11 +1,42 @@
 class Envelope
- attr_accessor :attack, :sustain, :decay
+ attr_accessor :duration, :attack, :sustain, :decay, :sample_rate, :total_frames
 
  def initialize(options = {})
- @attack = options[:attack]
- @sustain = options[:sustain]
- @decay = options[:decay]
+ @duration = options[:duration]
+ @attack = options[:attack] # in seconds ex: 0.15
+ @sustain = options[:sustain] # percentage ex: 30
+ @decay = options[:decay] # percentage ex: 60
+ @sample_rate = 22050
+ @total_frames = @sample_rate * @duration
  end
 
+ def attack_frames
+ attack_frames_count = (@sample_rate * @attack).to_i
+ growth_rate = (1.0 / attack_frames_count.to_f)
+ attack_frames = Array.new(attack_frames_count){ |index| index * growth_rate }
+ attack_frames
+ end
+
+ def sustain_frames
+ sustain_frames_count = (@total_frames - attack_frames.length) * (@sustain.to_f / 100.0)
+ sustain_frames = Array.new(sustain_frames_count) { 1 }
+ sustain_frames
+ end
 
+ def decay_frames
+ decay_frames_count = (@total_frames - attack_frames.length) * (@decay.to_f / 100.0)
+ decay_rate = (1.0 / decay_frames_count)
+ decay_frames = Array.new(decay_frames_count){ |index| index * decay_rate }.reverse
+ decay_frames
+ end
+
+ def envelope_frames
+ envelope_frames = attack_frames + sustain_frames + decay_frames
+ if envelope_frames.length < @total_frames
+ remainder = @total_frames - envelope_frames.length
+ filler = Array.new(remainder){ 0 }
+ envelope_frames += filler
+ end
+ envelope_frames
+ end
 end

lib/music_theory/note.rb

@@ -10,7 +10,7 @@ class Note
 
  def initialize(options = {})
  @frequency = options[:pitch] ? options[:pitch].frequency
- : options[:frequency].to_f || 440 # pitch ex) Pitch.new(:Ds, 3)
+ : options[:frequency].to_f || 440 # pitch ex: Pitch.new(:Ds, 3)
  @duration = options[:duration] || 1.0 # Number of seconds per note
  @distort = options[:distort] || false
  @envelope = options[:envelope]
@@ -41,6 +41,7 @@ def samples
  sample
  end
  samples = distort!(samples) if distort
+ samples = envelope!(samples) if envelope
  samples
  end
 
@@ -57,7 +58,10 @@ def distort!(samples)
  end
 
  def envelope!(samples)
- nil # fill-in after i've built the Envelope class
+ envelope_frames = @envelope.envelope_frames
+ zipped_frames = samples.zip(envelope_frames)
+ enveloped_samples = zipped_frames.map! { |i| i[0] * i[1] }
+ enveloped_samples
  end
  end
 end

test/envelope_test.rb

@@ -2,6 +2,18 @@
 
 class TestEnvelope < MiniTest::Test
  def setup
+ duration = 3.0
+ @envelope_note = MusicTheory::Note.new(pitch: Pitch.new(:A, 4),
+ duration: duration,
+ envelope: Envelope.new(duration: duration,
+ attack: 0.15,
+ sustain: 10,
+ decay: 70),
+ output_file_name: 'delete_me')
+ end
 
+ def test_hear_results
+ puts @envelope_note
+ @envelope_note.play
  end
 end