[hpsdr] FFT latency

[G3XJP]

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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