title: FFT lots of detail around certain frequency
body: <p>I have an arbitrary signal and I need to know the frequency spectrum of the signal, which I obtain by doing an FFT.  The issue is, I need lots of resolution <em>only</em> around this one particular frequency.  The issue is, if I increase my window width, or if I up the sample rate, it goes too slow and I end up with a lot of detail everywhere.  I only want a lot of detail in one point, and minimal detail everywhere else.</p>
  
  <p>I tried using a Goertzel filter around just the area I need, and then FFT everywhere else, but that didn't get me any more resolution, which I suppose was to be expected.</p>
  
  <p>Any ideas?  My only idea at the moment is to sweep and innerproduct around the value I want.</p>
  
  <p>Thanks.</p>