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Hi David,<br>
<br>
Let me preface this by saying that I have great interest in this
project; however, I'm not personally doing any of the coding as I'm
busy with other things. So, those who are coding, and possibly
learning as they go, may have alternative inputs.<br>
<br>
First of all, one must process the entire sample stream. It is not
acceptable to skip any samples as the discontinuities create
problems.<br>
<br>
Secondly, my approach would be to build overlap-save filters where
the forward FFT uses the original wideband sample stream and is
common for all outputs being served. However, each output has its
own Inverse FFT and the time-domain decimation is done in the
frequency domain before the inverse FFT which means that each
inverse FFT is much smaller than the original forward FFT. Using
this approach, the Jetson (or alternative server) would be serving
time domain samples and preserving all the flexibility that implies.<br>
<br>
That's a brief explanation of ONE way to approach the solution.
This is a very interesting project in that it should permit serving
a very large number of "slices".<br>
<br>
73,<br>
Warren NR0V<br>
<br>
<div class="moz-cite-prefix">On 9/4/2014 9:23 AM, David Bridgham
wrote:<br>
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<font face="Times New Roman, Times, serif">I've been mulling over
this idea of using the Jetson board to do an FFT of the entire
(mostly) sample stream to then make the frequency-domain signal
available to applications. Seems very intriguing and I love
hearing about entirely new ways of approaching problems.<br>
<br>
I'm curious though. When designing a codec, one chooses the
parameters for the FFT very carefully. The sampling rate is
given to you by the sample stream coming in (though you may
decimate to change that) but you pick the size of the FFT, the
overlap between blocks, and the window function all to make the
FFT bins show up just how you want them.<br>
<br>
With this new architecture, all those choices are made up front
and all the codecs running behind it have to use them. So my
question is, is there a way in the frequency domain to convert
from one to another? Can you simply average a bunch of FFT bins
together to get larger bin sizes and interpolate between bins if
you want smaller? Or do you have to do an IFFT back to the time
domain and then FFT again to change anything?<br>
<br>
I usually get about halfway through a DSP book before I get
bogged down so maybe this is all covered in later chapters.<br>
<br>
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