Re: [Discuss-gnuradio] Underruns using the simplest gnuradio-companion flow graph

[Tom Rondeau]

On Tue, Nov 20, 2012 at 3:42 PM, Olof Tangrot <address@hidden> wrote:
> Hi.
> I have tried the simplest possible flow-graph. A
> sine-source->Throttle->Audio-sink. But I get about 1 Hz drop outs and the
> message pane keeps writing aU.
> Using top the  process seems to laod the system less than 2 % and the total
> load on both processor kernels is well below 20 %. The samling rate is 48k.
> It does not seem to
> be possible to lover the sampling rate due to limitations of my sound card
> (which probably sucks anyway). I am using Fedora 16 on an AMD 64-bit
> machine.
>
> So is this really a processor capacity issue. I have sort of hard to believe
> that the the processor wont be able to compute 48000 sines per second and
> feed it to the sound card but there are of course a lot of layers in
> between. Any way rtl_fm seem to be able to feed data to aplay from a
> RTL2832U DVB-T recieiver without any problems so my machine is not totally
> slow.
>
> Isn't there anything I can do to improve the real-time performance of
> gnuradio-companion?
>
> Some kind of buffer to add to the flow-graph or something that is possible
> to tune in the operating system?
>
> Regards
>
> Olof

Olof,

Don't use the throttle block when you have another rate-limiting
system in your graph. You're audio sink will provide the rate control
in this case. With throttle and the audio sink, you've just created a
two-clock problem where one clock (throttle) is pretty bad.

Tom