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

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] question about overruns with simple flowgraph
Date: Mon, 05 Aug 2013 21:17:33 -0400
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16

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.


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".

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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