Re: [Discuss-gnuradio] First time user - fm radio tutorial has choppy audio

[Tom Rondeau]

On Wed, Jan 14, 2015 at 12:53 PM, Marcus D. Leech <address@hidden> wrote:

On 01/14/2015 12:44 PM, Chris Hallinan wrote:

Greetings, I'm a first time user of gnuradio.  Kudos to the developers, it only took me about a day to build gnuradio + gr-osmosdr (for my el-cheapo rtl2832 dongle) from source, including getting a basic FM broadcast receiver sort-of running.  Host Ubuntu 14.04 on a very fast Dell 8-core server platform.

I've prototyped an FM receiver as described in the tutorial at the bottom of this page:

http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorial_Hardware_Considerations

However, when I run it, and set the center frequency to a close-by FM station, although I can hear actual broadcast audio snippets, meaning that it's actually receiving a coherent signal, it is very choppy, with audio snippets being played in a very choppy, almost rhythmic fashion.  The console window on gnuradio-companion shows a continuous series of aUaUaU, etc.

I'm guessing this might be an underrun situation somewhere, but that is speculation.  I'm using parameters provided by the tutorial including a sample rate 250K.  I've tried moving the sample rate around, but without much improvement.  Dropping it down significantly destroys all hints of intelligence in the signal ;)  Am I overtaxing the capabilities of this rtl-sdr dongle?

I have a reasonable (and growing) understand of the core concepts, but could use some help on the learning curve.

Any advice appreciated.

-Chris

--

Life is like Linux - it never stands still.

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You almost certainly have a sample-rate mismatch somewhere in the flow--likely, your audio sink is configured for a sample-rate other than what
  the hardware (or PulseAudio) can support.  Sometimes also, PulseAudio gets into trouble and gets all under-runny.   I'd go with Alsa direct if it
  were my problem, and skip Pulse entirely.

-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

The manual gives you a few hints for different possible device names you can try:

http://gnuradio.org/doc/doxygen/classgr_1_1audio_1_1sink.html

Unlike Marcus, I've always had better luck with pulse that direct alsa. But we have very different systems and use different Linux versions, so ymmv.

Tom