[hpsdr] FFT latency

[Andrew Siede]

How woould it be to
-recieve the signal from AtoD
-convert it using a digital version of a regular reciever to get close to the audio out
-use FFT and IFFT to clean it up
as you are converting a smaller spectrum it will need less overhead to do the fft

-----Original Message-----
From: G3XJP [mailto:G3XJP at RhodesG3XJP.plus.com]
Sent: 07 April 2015 09:46
To: Simon Brown
Cc:Hpsdr at lists.openhpsdr.org
Subject: Re: [hpsdr] FFT latency
  
gm Simon,
1) I don't have and don't want a waterfall/spectrum display and
2) my SDR does not run on a PC let alone Windows.  It runs on a dedicated
radio.
I do have to have Fourier and his inverse in the real-time signal path -
because I need to get into the freq domain, do the Noise Reduction stuff and
then get back to the time domain.  In that sense, FFT and IFFT are pure
overheads, a means to an end.  And I would have to forget the whole idea if
they produced inherent delays that would make ANY radio on ANY platform
unuseable.  20ms is acceptable.  Only just.  Peter G3XJP
  
Simon Brown wrote:
   

Peter,
  
You don't have to perform FWD / INV FFT in the demodulation path at all.
Essentially there are two IQ paths in a generic design:
  
1) For the waterfall / spectrum display,
2) For demodulation.
  
Demodulation can get down to < 20ms on Windows if you're careful,
using WASAPI audio API helps a lot  .
  
Simon Brown G4ELI
http://v2.sdr-radio.com
  


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