# Audio Sink Producing UaUaUaUa

**URL:** <https://www.ruby-forum.com/t/audio-sink-producing-uauauaua/234741>\
**Category:** GNU Radio\
**Created:** [March 25, 2015, 6:44pm UTC](https://www.ruby-forum.com/t/audio-sink-producing-uauauaua/234741 "2015-03-25T18:44:05Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [March 25, 2015, 6:44pm UTC](https://www.ruby-forum.com/t/audio-sink-producing-uauauaua/234741/1 "2015-03-25T18:44:05Z")

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Hello,

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.

v/r,  
Rich

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**Author:** ![reback](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@reback](https://www.ruby-forum.com/u/reback)\
**Post date:** [March 25, 2015, 7:01pm UTC](https://www.ruby-forum.com/t/audio-sink-producing-uauauaua/234741/2 "2015-03-25T19:01:25Z")

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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.

Greetings,  
Marcus

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

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<div class="post-metadata">

**Author:** ![reback](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@reback](https://www.ruby-forum.com/u/reback)\
**Post date:** [March 25, 2015, 7:23pm UTC](https://www.ruby-forum.com/t/audio-sink-producing-uauauaua/234741/3 "2015-03-25T19:23:02Z")

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Marcus,

Every sample rate I try produces the UaUaUa pattern. I tried all the  
built  
in rates as well as 192 kHz.

When I run the gr-aduio dial-tone example, I get garbled noise as  
output,  
instead of a dial tone, with the noise source turned off. Do you have an  
idea what this might point to?

Pandora produces perfectly normal music coming out of my speakers as a  
sanity check.

v/r,  
Rich

On Wed, Mar 25, 2015 at 10:59 AM, Marcus Müller  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)