[hpsdr] FFT latency

[Simon Brown]

Peter,

 

OK - I understand. Myself I find LMS good with more taps.

 

Simon Brown G4ELI
http://v2.sdr-radio.com

 

From: G3XJP [mailto:G3XJP at RhodesG3XJP.plus.com] 
Sent: 07 April 2015 10:03
To: Simon Brown
Cc: Hpsdr at lists.openhpsdr.org
Subject: Re: [hpsdr] FFT latency

 

Simon, it is precisely LMS noise reduction and auto-notch that I am
replacing.  COS - in brief - I don't like listening to voices coming out of
a drain-pipe.  The freq domain solution is way more effective.   But at a
price, namely inherent delay.  So I'm not looking for other solutions.  I
just want to be sure those inherent Fourier delays are .... ummmm ....
inherent.  Peter G3XJP

Simon Brown wrote: 

Peter,
 
One alternative to FFT-based noise reduction would be adaptive LMS noise
reduction with ~ 99 taps (or a variable number of taps). LMS can also be
used with great effect for an automatic notch filter.
 
Simon Brown G4ELI
http://v2.sdr-radio.com
 
 
-----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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