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Re: [Discuss-gnuradio] Streaming Funcube Dongle Pro+ over UDP


From: Vanush Vaswani
Subject: Re: [Discuss-gnuradio] Streaming Funcube Dongle Pro+ over UDP
Date: Fri, 9 Aug 2013 09:22:01 +1000

Hi,

If i add a rational resampler to match the audio rate before the UDP sink, I can get a continuous output, but it's of terrible quality due to the loss of information. 

How does the flowgraph work having a sample rate 'mismatch' when the FCDPP block is in the same graph?! 

Could you give me a hint in working around this issue?

Sent from my iPhone

On 09/08/2013, at 5:01 AM, Marcus Müller <address@hidden> wrote:

Hi Vanush,

as Iain pointed out, the sound card _enforces_ a low sample rate by being an actual piece of hardware;
therefore, 44.1ksamples/s "leave" your flowgraph at the audio sink, while you feed it 192ksamples/s from the
funcube.
A faster computer _might_ help, but first adjust the sampling rates (although if your computer is really fast travelling away from you, the 192ks/s might hit him with 44.1ks/s, but I guess if you get a computer that fast, it might be the end of everything.)

 08.08.2013 20:18 Vanush Vaswani:
Ok,

would a faster computer help? I am running the receiver on a 2008 Macbook air, might be a bit slow for modern standards.

On Fri, Aug 9, 2013 at 4:13 AM, Marcus Müller <address@hidden> wrote:
Hi,
your warning points to the UDP source: Since your receiver can't process all the samples that it gets
via UDP, and the UDP source runs out of buffering capacity, it starts to drop UDP packets.

There are two things that you must do:
1) The Samples for the audio sink _must_ be resampled to the right sound card sampling rate,
e.g. 44.1kHz, otherwise that card will see a highly frequency-shifted version of the real signal
2) take care that the samples from the network get processed fast enough so that there will be no dropping.

Best Regards
Marcus

Am 08.08.2013 18:09, schrieb Iain Young, G7III:

Different parts of the flow graph can have different sample rates.

You need to use the rational resampler so it's output matches what
your soundcard expects.

You may also need a complex to real somewhere. There are plenty of
examples for a FM receiver on the web.


Best Regards

Iain

On 08/08/13 16:56, Vanush Vaswani wrote:
How can I set the sampling rate on both ends to be the same? FCDPP
sampling rate is 192 KHz.

If I include an audio sink, is the rate of the flowgraph controlled by
the sound card sampling rate?

Attached are my .grc files.


On Thu, Aug 8, 2013 at 11:34 PM, Alexey Bazhin <address@hidden
<mailto:address@hidden>> wrote:

    Do you set sampling rate 192000 on both ends? Post your grc files.

    On Thu, 8 Aug 2013 14:09:42 +1000
    Vanush Vaswani <address@hidden <mailto:address@hidden>> wrote:

     > Hi there,
     >
     > I'm trying to stream the FCDPP over UDP to a another computer
     > The setup is as follows
     >
     > FCDPP Source -> UDP Sink
     >
     > For the receiver,
     >
     > UDP Source -> LPF -> Quadrature demod -> FM Deemph -> LPF -> Audio
     > sink
     >
     > Unfortunately, when I run the flowgraph on the receiver end, I only
     > hear a bunch of clicks.
     > The console is full of messages "WARN: Too much data; dropping
     > packet.". WX GUI FFT Sink and Waterfall seem to work, though with the
     > same messages.
     >
     > Any hints to rectify this issue?


    --
    Alexey Bazhin <address@hidden <mailto:address@hidden>>




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