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James Peroulas james at peroulas.comMessage: 1 > Date: Thu, 6 Sep 2012 05:22:25 +1000 > From: Ben Ryan <benryanau at hotmail.com> > To: <osmocom-sdr at lists.osmocom.org> > Subject: "Best" sampling rate? > Message-ID: <SNT139-W176A4A72E42D16D41CA612B6A90 at phx.gbl> > Content-Type: text/plain; charset="iso-8859-1" > > > > > > Come to think of it, I've also found some samplerates to be better than > others. No further info to share beyond the fact that I've noticed it too. > > Drops at higher samplerates are probably due to your CPU, IO latency, etc > (esp if virtualised). You should be able to run 2.048Msps with AF rate of > 44.1khz with next to no drops and smooth carrier audio. If not, and your > CPU isn't maxed out, likely you have a latency or bandwidth issue. > What's the rig you're running on? > > There appears to be an interaction between AF samplerate and IQ > samplerate.. under HDSDR/Win32 anyways. > It might well reduce skips and cpu load if the two rates were cleanly > divisible but I haven't tried to work the theoreticals out.. > > I just set 3.2Msps for spectrum scoping, then narrow to around 1.2Msps for > FM/AM work. The audio rate is usually 44.1khz although sometimes whendoing > an "audio print" of a signal using DRM mode I'll up it to 48khz. On the > Core2Duo I get quite a few dropped samples at 3.2Msps/48khz though - it's > hitting the limits for this system as-is (it's running VMWare MS plus it's > got layers of drivers on it). > > Another thing to consider if under Win32: differing versions of libusb, > ExtIO_RTL, ExtIO_USRP, rtl2832u++.dll files all behave differently wrt cpu, > samplerates and drops. > I haven't documented my findings yet but there's a complex relationship > between the above elements and tuner range.. some RTL libs will permit > 50mhz-~2000mhz, others puke at various spots on the dial etc. > Thanks for the inspiration. I actually re-wrote my code to use async mode and now I'm getting reliable captures up to 1.92MSPS (my desired sampling rate). I was using sync mode but apparently that's not fast enough to capture all samples! BR, James -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/osmocom-sdr/attachments/20120906/2b9a3e1f/attachment.htm>