Marcus,
Sorry for the late reply on this, I've been upgrading my hardware and
I'm just catching up. Here is my issue, in Spectrum lab if I provide
a FFT Input length of 65536 on a 192Ksps stream, I get the following
characteristics:
Effect of FFT settings with fs= 192.000 kHz:
Width of one FFT-bin: 2.92969 Hz
Equiv. noise bandwidth: 4.39453 Hz
Max freq range: 0.00000 Hz .. 96.0000 kHz
FFT window time: 0.341 s
Overlap from scroll interval: 98.4 %
It runs quite fast. If I provide the same FFT size to WX GUI FFT
sink, it basically hangs. Do you know why?
Regards,
Mark McCarron
Because apparently SpectrumLab is using an overlapped FFT
implementation. The one in wXGUI doesn't. Further, the wxGUI
implmentation has far
too much Python involved in processing samples, so trying to process
65536 samples at a time is likely sluggish, to the point that it can't keep
up in real time.
The underlying FFT implementation itself is very fast--Gnu Radio uses FFTW.
I've regularly built FFT filters with 250e3 taps, and they are able to
run in real time with sample rates into the many Msps.
So, if you do the math, a non-overlapped FFT implementation of 65536
bins at 192Ksps means 2.92 FFTs/second. If the display update rate is
more than that, there's no way to actually produce an update rate
faster than 2 per second under those circumstances, with a non-overlapped
FFT.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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