Ruby FFT of .wav Test.rb

#!/user/bin/env ruby

require 'rubygems'
require 'wavefile'
require 'fftw3'
require 'fastercsv'

# needs to be mono, or you'll need to discard a channel, or combine channels
w = WaveFile.open('sample.wav')

samples = w.sample_data[0, [w.sample_rate * 10, w.sample_data.size].min]
duration = samples.size / w.sample_rate

na = NArray.float(2, samples.size)
samples.each_with_index do |v, i|
  na[0, i] = i.to_f / w.sample_rate.to_f
  na[1, i] = v # if the file is stereo, do v.first or v.last or v[0] + v[1]
end

fa = FFTW3.fft(na)
fa = fa.real.abs # you probably need absolute values for magnitudes of a frequency to make sense

FasterCSV.open('output.csv', 'w') do |csv|
  0.upto((fa.total / fa.dim) - 1) do |i|
    csv << fa[true, i].to_a
  end
end