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

[Marcus Müller]

Hi Chris,
On 01/14/2015 06:44 PM, Chris Hallinan wrote:
> Greetings, I'm a first time user of gnuradio.
Welcome!
> 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.
But speculation that's probably correct :)
aU is audio underrun, which means you're most probably supplying samples
at a rate that's lower than the audio sink is configured to accept.
> 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?
Probably not, since you're doing so well this far! Basically, use a
sampling rate that works, and decimate to exactly the sampling rate you
need for your audio sink.

>
> I have a reasonable (and growing) understand of the core concepts, but
> could use some help on the learning curve.
>
> Any advice appreciated.
>
see above :)

Greetings, and happy hacking,
Marcus