Re: [Discuss-gnuradio] Audio underrun when using Audio Sink

[Kevin Reid]

On Jun 18, 2016, at 19:07, Paul S <address@hidden> wrote:
> Currently, I am trying to send data over ultrasound signals based on [1],
> using the audio sink and several sources. The problem is that I get often
> consecutive audio underruns (for several seconds straight).
> This is my flowgraph:
> <http://gnuradio.4.n7.nabble.com/file/n60547/flowgraph.jpg> 
> The TunSource just reads data from a Tun-Device but I get these underruns
> with other blocks like the depicted Socked PDU or even a File Source, too
> (though not as frequently).
> So it basically boils down to (Byte?)-Source -> GFSK Mod -> Rational
> Resampler -> Frequency Xlating FIR Filter-> Audio Sink.
[...]
> My assumption is that this is a "two clock problem" which I've read about in
> other posts.

If you get this underrun when you are using a file source then you definitely 
do not have a two-clock problem, because the only clock in your flowgraph is 
the audio sink.

That being the case, the only reason you should see underruns is if your CPU is 
not able to keep up, but that seems unlikely at your low sample rates. Check 
your system monitor for any cores running at 100% -- that would indicate that 
some one of your blocks is doing too much work.

If that actually is the problem, the most likely culprit is your 200:1 
resampler -- you could try breaking it up into multiple stages (e.g. 
interpolate by 20 then interpolate by 10) or using a FFT filter block to do the 
antialias filtering.