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<div class="moz-cite-prefix">On 6/23/2012 7:01 AM, Chris Albertson
wrote:<br>
</div>
<blockquote
cite="mid:CABbxVHv+a-vF0iCYob99SyQj3GKmEexRDLJzj2YLq44fR=RaWA@mail.gmail.com"
type="cite">
<pre wrap="">So you have decided NOT to use an FFT? You can save a lot of CPU
cycles if you do dump the data stream into FFTW.
The reason is because there is this neat trick, if you take the FFT,
multiply that by an implies function and then take the inverse FFT you
have just applied any number of convolutions. This pays off in a big
way if you want to do more with the data then just detect one USB
signal.</pre>
</blockquote>
<font face="Tahoma">That is correct, but do not forget that using
FFTs is like applying a "circular"convolution to the signal,<br>
while what you really want is a "linear" convolution. So, before
taking the inverse FFT, you must apply<br>
either the "overlap and save" or the "overlap and discard"
algorithm.<br>
<br>
They are quite well described in the Openheimer & Shafer well
known textbook on Digital Signal Processing.<br>
</font><br>
<div class="moz-signature">-- <br>
<i><b>73 Alberto I2PHD</b></i>
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