I am using gnuradio companion to run a simple test, in which I just connect a signal source to an audio sink. They have the same sample rate, and the signal source is a sine wave, amplitude is 0.1, frequency 1kHz, offset 0. When I make the sample rate for both to be 48kHz, the audio is very choppy and sounds pretty bad. When make the sample rate for both equal to 16kHz, it sounds much better but is still skipping at a period that is less than a second I think. In both cases I see the aUaUaU, indicating underrun. What can cause the underrun in this case?
I'm running Centos 6.4 in a virtual machine. I left the audio device field blank in the audio sink block in grc, and I believe it is using Pulse, or at least putting "pulse" in that field produces the same effect.
I have been able to capture data from the rtl-sdr and scroll through its spectrum using WX widgets in grc, so everything else seems to be working.