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Re: [Discuss-gnuradio] Audio Sink Producing UaUaUaUa

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Audio Sink Producing UaUaUaUa
Date: Wed, 25 Mar 2015 18:59:27 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

Hi Richard,

these are audio Underruns, meaning that you did not supply the sound system with the samples it needs for continuous playback in time.
following an old FAQ entry [1]:
If you have RF hardware in your flow graph, you might be seeing the "two-clock problem": No two oscillators are exactly the same, so if your sample-producing hardware is a bit slower than it should be, or your sound card is a bit faster, than you'll see this.

Also possible is that you've used a sampling rate that your audio system doesn't actually support, and it automatically used a different one, so that you end up with the same problem as above, even when things *should* work (if the audio device actually consumed samples at the rate you specified). Try 44100 or 48000 Hz, these work on most sound cards.

Another reason is that your system is simply too slow at calculating samples, but that's unlikely on modern hardware, unless you do something very CPU-intense (e.g. a 400 tap filter, or something).

And yet another warning: Never ever use throttle in a flow graph with hardware. It gives you the two-clock problem (one clock being sleep() of your OS), AND it just "stops" samples in large chunks until enough time has passed that a large-scale average sample processing rate is met. On smaller scale, though, this leads to frequent underruns.


[1] http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#I-have-a-receiver-with-acoustic-output-and-keep-getting-aUaUaU-errors

On 03/25/2015 06:42 PM, Richard Bell wrote:

When I have an audio sink in my flowgraph, leaving the device field blank to default to speakers, I see a continuous stream of UaUaUaUa printed to the console. What is this telling me? Disabling the audio sink stops the Ua stream.


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