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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<br>
<br>
Simon Brown wrote:
<blockquote cite="mid:005d01d07110$47ebb730$d7c32590$@sdr-radio.com"
type="cite">
<pre wrap="">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
<a class="moz-txt-link-freetext" href="http://v2.sdr-radio.com">http://v2.sdr-radio.com</a>
-----Original Message-----
From: G3XJP [<a class="moz-txt-link-freetext" href="mailto:G3XJP@RhodesG3XJP.plus.com">mailto:G3XJP@RhodesG3XJP.plus.com</a>]
Sent: 07 April 2015 09:46
To: Simon Brown
Cc: <a class="moz-txt-link-abbreviated" href="mailto:Hpsdr@lists.openhpsdr.org">Hpsdr@lists.openhpsdr.org</a>
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:
</pre>
<blockquote type="cite">
<pre wrap="">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
<a class="moz-txt-link-freetext" href="http://v2.sdr-radio.com">http://v2.sdr-radio.com</a>
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