Maybe watch your CPU utilization with htop when you're recording with terminal command to /dev/null, and compare it to gnuradio with a null source.
If you take out or disable the audio source, the underflows should go away. On Tue, Mar 17, 2015 at 5:14 PM, Marcus Müller <marcus.muel...@ettus.com> wrote: > Hi Larry, > > if I understand correctly, then you're using the audio source as "input" > to your usrp_sink-terminated flow graph. > In that case, the "U"nderruns come from UHD, not the audio source; the > flow graph is not supplying samples fast enough. > > The problem might be systematic, for example if the rate change in your > flow graph does not reflect the actual rate ratio between your audio device > and the USRP -- e.g. the your audio device generates samples at 48kS/s, and > your USRP consumes them with 5MS/s, but you have an interpolation rate of > 100 (leading to a rate at which samples arrive at the USRP sink of 4.8MS/s; > these are all just exemplary numbers). > > Also possible, though, is that this is simply an extreme case of clock > mismatch: For example, assume the reference clock in your USRP is of by > 2ppm, making the "sample consume rate" (1+2e-6) times higher than it should > be, according to an imaginary "exact" clock. > Now, assume your sound card is a bit "slower" than it should be, so let > these should-be 48kS/s be (1-500e-6) times that what it should be. > That means that for every a USRP sampling rate of let's say 5MS/s, you'd > have around 2500 samples too little per second, which (there's around 250 > samples transportable per USB packet) is around 10 sample packets less than > the USRP consumes. > > Greetings, > Marcus > > [1] I pulled up the first sound chip datasheet I could find (TI PCM2903), > and it demanded +-500 ppm. > > > On 03/17/2015 03:30 PM, Larry Van Der Jagt wrote: > > Hello: > > Can anyone point me to some "color" on how to work with the Audio > Source. I am working examples to transmit FM Audio and have problems with > Underruns on the UHD:USRP Sink. > > The examples (from files.ettus.com/tutorials/Lab_5.grc and others) I am > running select Audio Source Arch:alsa and this seems to be a problem. > > I have tried to replace the Device name with plughw:0,0 as suggested in > the documetnation, but this does not seem to have an impact on the choice > of Audio arch: alsa > > If I replace the audio source with a signal source at the same sample > rate all is well, but the Audio Source implements UUUUUUUUUUUU. > > Using the suggestion of having the USRP expect a bit lower rate than the > audio can deliver seems to implement nearly limitless delay .... the voice > is received but only after a very long ... many seconds delay ... .... > > At this time I am using a B210 connected via USB3 to an I7 with plenty > of memory running Ubuntu 12.04 .... I have similar issues trying to use an > E310 as the transmitter ... > > Any direction would be appreciated. > > LVDJ > > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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