spectrum analyzer using resonance

spectrum.rb

require "wavefile"

class Oscilator
  def initialize(opt={})
    @freq = opt[:freq] || 440.0
    @sample_rate = opt[:sample_rate] || 44100
    @delta_time = 1.0 / @sample_rate
    # k/M (k = strength of spring, M = mass of object) => @k
    @k = (2.0*Math::PI*@freq)**2
    @m = opt[:mass] || 1.0
    @k *= @m

    # fliction. F = -mu*dx
    @mu = opt[:mu] || 100
    @mu *= @m # for convinience

    @x = 0
    @dx = 0
  end

  def step(pivot)
    @pivot = pivot
    ddx = (- @mu * @dx - @k * (@x - @pivot)) / @m
    dx_new = @dx + ddx * @delta_time
    x_new = @x + dx_new * @delta_time
    @dx = dx_new
    @x = x_new
  end

  attr_reader :x, :dx

  def amplitude
    @x
  end

  def velocity
    @dx
  end

  def potential
    (@k * ((@x - @pivot) ** 2) + @dx ** 2 / @m) / 2.0
  end

  def normalized_potential
    potential / (0.5 * @k)
  end
end

wav = WaveFile.open(ARGV[0])
data = wav.normalized_sample_data
if data[0].is_a?(Array)
  data = data.map {|pair| pair[0] }
end

osc_ary = [ 32, 64, 125, 250, 500, 1000, 2000, 4000, 8000 ].map do |freq|
  Oscilator.new(:freq => freq, :mu => 50)
end

data.each do |val|
  osc_ary.each do |osc|
    osc.step(val)
  end
  ary = osc_ary.map do |osc|
    "%.10f" % osc.normalized_potential
  end
  ary.unshift val
  puts ary.join(", ")
end