title: How can I get the ratio of two audio signals in the frequencies domain?
body: <p>I need to compare two audio signals, signal1 and signal2. Signal1 is a white noise. Signal2 is the same signal of signal1, with a particular equalization for cutting or for attenuating some frequencies. 
  How can I get the ratio of two audio signals in the frequencies domain? (e.g.: at the frequency of 100Hz, signal2 is attenuated by 50% compared to signal1).
  I need this information to process a third signal by applying the same equalization applied to transform signal1 in signal2.</p>
  
  <p>I used <a href="http://incanter.org/docs/parallelcolt/api/edu/emory/mathcs/jtransforms/fft/DoubleFFT_1D.html" rel="nofollow">this library</a> to process my data and pass from the time domain to the frequencies domain. This code is the same for signal1 and signal2.</p>
  
  <pre><code>DoubleFFT_1D fft1 = new DoubleFFT_1D (FFT_SIZE);
  double[] input1 = new double[FFT_SIZE];
  
  double[] fftBuff1 = new double[FFT_SIZE * 2];
  
  
  this.wavFileDoubleInputStreamMic.read(input1, 0, FFT_SIZE);
  
  
  for (int i = 0; i &lt; FFT_SIZE; i++){
      fftBuff1[2*i] = input1[i];
      fftBuff1[2*i+1] = 0;
  }
  
  
  fft1.complexForward(fftBuff1);
  </code></pre>
  
  <p>How can I use FFT results (from signal1 and signal2) to reach my goal? </p>