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Re: [Discuss-gnuradio] Transmit and receive suing GMSK


From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Transmit and receive suing GMSK
Date: Fri, 27 Apr 2012 10:25:59 -0400

On Fri, Apr 27, 2012 at 1:58 AM, Jamie Wo <address@hidden> wrote:
> Hi Tom,
>
> Thanks for your reply. It works.
>
> I met another strange problem.  When I use Wav file source --> audio sink, I
> can hear the sound in the wav file clearly. However, when I want to hear the
> file and transmit it using UHD sink at the same time, audio underrun "aUaU"
> occur. The flow graph is like:
>
> Wav file source --> Package Encoder --> GMSK Mod --> UHD sink.
>                        --> Audio sink
>
> Do you know what is the problem?
>
> Jamie

When you get the audio underruns, do you hear the sound at all? Or are
the underruns continuous.

If they are continuously happening, you have a mismatch in the sample
rate at some point in the flowgraph.

If it's intermittent, that's probably the notorious "two-clock
problem." Both the USRP and audio device have their own clocks that
are running at different rates, though close. Since they will slip
against each other, the frequency of which is dependent on how
different the clocks are, then you'll have this problem. Usually it's
not so bad that you can't hear things, and you might get a clicking
sound as there's some loss here and there due to it.

Tom



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