Re: [Discuss-gnuradio] question about overruns with simple flowgraph

[Stephen]

On 8/5/2013 8:17 PM, Marcus D. Leech wrote:
> On 08/05/2013 09:00 PM, Nick Foster wrote:
>>
>>
>> A couple of seconds seems pretty fast, however. Make sure you're
>> resampling the audio to a rate which is actually supported by your
>> soundcard.
>>
>> --n
>>
> The two-clock problem tends to manifest as the occasional "click" or
> occasional 'O'.
> 
> But if the rates between USRP source, and audio sink are significantly
> mis-matched, you end up with overruns very quickly, since buffers will
>   start to fill up to exhaustion, since the sink isn't taking samples as
> fast as they're being produced.
> 
> There's no "magic" rate-adaptation in Gnu Radio.  If you have a filter
> block that is decimating down to, let's say, 50kHz, and then feed it into
>   an audio sink that's expecting data at 48kHz, things will get stuffed
> pretty quickly.  Just because a (hardware) sink is expect data at
>   some rate, doesn't mean that Gnu Radio automatically "tweaks" the flow
> graph to deliver data at that rate.  Gnu Radio is a streaming
>   architecture, it doesn't actually inherently "know" about sample
> rates, so you have to take care of decimating/interpolating data streams
>   so that things "match".
> 
> 

Ahhhh, now I see. I am getting frequent 'O' and audio clicks and pops. I
had played with the various rates till I got the final audio decimation
very close to an integer value but not quite. The integer value used was
a little lower than needed. I adjusted things some more and got a set of
rates that resulted in an integer decimation for the audio lp filter and
that fixed the problem.

The link to the previous discussion was interesting.

thanks, guys
stephen