f-modes.rb

require 'bundler'
Bundler.require

twelth_root_of_two = (2 ** (1.0/12))

current = 220.0
note_frequencies = [current]
50.times do
  current *= twelth_root_of_two
  note_frequencies.push current
end

T = 2
S = 1


all_notes       = []
current_mode    = [T, T, S, T, T, T, S]
current_start   = 0

8.times do
  current = current_start
  mode_frequencies = [note_frequencies[current]]
  current_mode.each do |interval|
    current += interval
    mode_frequencies.push note_frequencies[current]
  end

  all_notes       += mode_frequencies
  current_start   += current_mode.first

  current_mode.rotate!
end


sample_rate       = 22050 # frames per second
note_duration     = 0.5    # seconds
frames_per_note   = (sample_rate * note_duration).to_i

samples = []

all_notes.each do |frequency|
  cycles_per_frame = frequency / sample_rate
  increment = 2 * Math::PI * cycles_per_frame
  phase = 0

  frames_per_note.times.map do
    samples << Math.sin(phase)
    phase += increment
  end
end

filename = 'f.wav'

format = WaveFile::Format.new :mono, :pcm_16, sample_rate
buffer_format = WaveFile::Format.new :mono, :float, sample_rate
WaveFile::Writer.new filename, format do |writer|
  buffer = WaveFile::Buffer.new samples, buffer_format
  writer.write buffer
end

`afplay f.wav`