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Alan Corey alancorey at yahoo.comStill no luck. If I use -R for raw mode a little more data gets through (as seen by file sizes or the Play progress meter) but it seems to be less intelligible if anything. When I write to a file, the size is always in chunks of 16384 bytes (0x4000 or 2^14). At a sample rate of 24000 that's 1/3 second, which is about right compared to what I hear. Without using -R, this doesn't repeat for about a minute. That 16384 must be some buffer size or something in the rtl_fm program, but I haven't found it yet. I think this is supposed to repeat often enough to be continuous. Could computer speed be an issue? I'm on a single core P4 at 3.2 GHz. From rtl_fm -f 146970000 -f 146985000 -f 146910000 -f 146940000 scan2.dat I got this which looks like bursts of noise as rtl_fm is scanning, still all within about 1/3 second: http://ab1jx.webs.com/toys/dongle/scan2.dat.gif There's a curious ripple in the baseline which doesn't quite look like power supply ripple, more like something from some filter. Alan ----- Radio Astronomy - the ultimate DX ----- Original Message ----- > From: Adam Nielsen <a.nielsen at shikadi.net> > To: Alan Corey <alancorey at yahoo.com> > Cc: "osmocom-sdr at lists.osmocom.org" <osmocom-sdr at lists.osmocom.org> > Sent: Monday, December 31, 2012 1:28 AM > Subject: Re: Trying to use rtl_fm, etc > >> With rtl_fm, I get a tiny burst of audio about once a minute. >> >> A fresh run: >> freebie# rtl_fm -N -f 162550000 - | play -t raw -r 32k -e signed-integer -b > 16 >> -c 1 -V 4 - > > Just FYI, you can see here that: > >> Output at 24000 Hz. > > However you have told 'play' to play the audio at a sampling rate of > 32kHz, even though the audio data is only arriving at 24kHz. So you will get > stuttering as the audio buffer keeps running out and waiting for more data to > arrive. > > For me (under Linux), I get best results using the -r option to rtl_fm to set > the output audio sampling rate to 48kHz, then tell play to play at 48kHz too. > This way my system doesn't have to resample it to 48kHz before it can mix > the stream into the system-wide audio output. > > Note that the -s option sets the signal bandwidth and -r sets the output audio > sampling rate. A lot of people misunderstand the purpose of the -s option, > however you shouldn't need it unless you are trying to receive data signals. > -W and -N set -s to the correct values for voice transmissions. > > I would also suggest playing a .wav file with the same 'play' options > just to make sure your system can play mono audio at low sampling rates. I know > my sound card drivers won't (possibly because I am using a SPDIF connection > to an external amplifier) so I need the Linux audio system to upmix it to 48kHz > 16-bit stereo or I won't hear anything. > > Cheers, > Adam. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/osmocom-sdr/attachments/20130101/a6b7b6d2/attachment.htm>