title: white noise has flat power spectral density
body: <p>I am trying to prove that the white noise has constant power spectral density using matlab 
  but the amplitude of the spectrum looks like random amplitude.</p>
  
  <p>can anyone tell me why?</p>
  
  <p>here is my code.</p>
  
  <pre><code>noise = randn(1,10000);
  fft_noise=fft(noise);
  plot(abs(fft_noise(1:5000)))
  </code></pre>
  
  <p>thanks.</p>