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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Peter,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>OK – I understand. Myself I find LMS good with more taps…<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Simon Brown G4ELI<br>http://v2.sdr-radio.com<o:p></o:p></span></p></div><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> G3XJP [mailto:G3XJP@RhodesG3XJP.plus.com] <br><b>Sent:</b> 07 April 2015 10:03<br><b>To:</b> Simon Brown<br><b>Cc:</b> Hpsdr@lists.openhpsdr.org<br><b>Subject:</b> Re: [hpsdr] FFT latency<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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: <o:p></o:p></p><pre>Peter,<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>One alternative to FFT-based noise reduction would be adaptive LMS noise<o:p></o:p></pre><pre>reduction with ~ 99 taps (or a variable number of taps). LMS can also be<o:p></o:p></pre><pre>used with great effect for an automatic notch filter.<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Simon Brown G4ELI<o:p></o:p></pre><pre><a href="http://v2.sdr-radio.com">http://v2.sdr-radio.com</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>-----Original Message-----<o:p></o:p></pre><pre>From: G3XJP [<a href="mailto:G3XJP@RhodesG3XJP.plus.com">mailto:G3XJP@RhodesG3XJP.plus.com</a>] <o:p></o:p></pre><pre>Sent: 07 April 2015 09:46<o:p></o:p></pre><pre>To: Simon Brown<o:p></o:p></pre><pre>Cc: <a href="mailto:Hpsdr@lists.openhpsdr.org">Hpsdr@lists.openhpsdr.org</a><o:p></o:p></pre><pre>Subject: Re: [hpsdr] FFT latency<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>gm Simon,<o:p></o:p></pre><pre>1) I don't have and don't want a waterfall/spectrum display and<o:p></o:p></pre><pre>2) my SDR does not run on a PC let alone Windows. It runs on a dedicated<o:p></o:p></pre><pre>radio. <o:p></o:p></pre><pre>I do have to have Fourier and his inverse in the real-time signal path -<o:p></o:p></pre><pre>because I need to get into the freq domain, do the Noise Reduction stuff and<o:p></o:p></pre><pre>then get back to the time domain. In that sense, FFT and IFFT are pure<o:p></o:p></pre><pre>overheads, a means to an end. And I would have to forget the whole idea if<o:p></o:p></pre><pre>they produced inherent delays that would make ANY radio on ANY platform<o:p></o:p></pre><pre>unuseable. 20ms is acceptable. Only just. Peter G3XJP<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Simon Brown wrote:<o:p></o:p></pre><pre> <o:p></o:p></pre><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><pre>Peter,<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>You don't have to perform FWD / INV FFT in the demodulation path at all.<o:p></o:p></pre><pre>Essentially there are two IQ paths in a generic design:<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>1) For the waterfall / spectrum display,<o:p></o:p></pre><pre>2) For demodulation.<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Demodulation can get down to < 20ms on Windows if you're careful, <o:p></o:p></pre><pre>using WASAPI audio API helps a lot :) .<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Simon Brown G4ELI<o:p></o:p></pre><pre><a href="http://v2.sdr-radio.com">http://v2.sdr-radio.com</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre></blockquote><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre></div></body></html>