Re: [Discuss-gnuradio] FFT Playback

[Marcus Müller]

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With most hardware interfaces, you get notifications when your
driver/interface starts dropping samples -- with UHD you'd see loads
of 'O' indicating overflows.
If you don't see that, there is something really wrong. How does your
data acquisition take place? 50Msps is really a lot for an average PC
if you do filtering; I don't know how your low pass filter looks, but
I think it's probably causing to much computational load for your
computer to process the incoming samples in real time.

Greetings,
Marcus

On 04.12.2013 12:39, Paul B. Huter wrote:
> There must be something with my record, because my 20 seconds of
> running only produces about a 180MB file. I am not seeing any
> indications of dropped data, though. I am recording to a RAMDisk,
> but I get the same results recording to my HDD.
> 
> Does anyone have recommendations for how to ensure I get my data
> recorded? I really think that if I cam record the data, playback
> will be more what I am looking for.
> 
> Paul B. Huter On Dec 4, 2013 1:20 AM, "Marcus Müller"
> <address@hidden> wrote:
> 
> Hi Paul!
> 
> I'm gonna go ahead and rearrange parts of your message for the ease
> of reply:
>>>> My datafile was recorded for about 20 seconds at a sample
>>>> rate of 50Msps through a low-pass filter to only capture
>>>> 0-30MHz.
> 50Msps * 20s = 1Gs (you're sure your file is 8GB in size?) should
> be plenty enough, so my guess was totally astray.
> 
>>>> Looking at the configuration for my FFT, and changing
>>>> 'Refresh Rate' from the default '15' to '1M' gives me some
>>>> extra playback.
> what gui toolkit are you using? wx or qt? However, a refresh rate
> of one million frames per second... doesn't even remotely make
> sense. Since there is no way that your file source can supply
> 1024Msps for the GUI sink, even without throttling, I don't know
> what the (wx or qt or whatever) FFT sink does in that case. I'd 
> have to read the source code...
> 
>>>> I like the way the waterfall looks, but I'm having the same
>>>> issue as the FFT.
> 
> Ok, this is confusing. The waterfall sink should basically be able
> to have one pixel of display per sample going in. And with 1
> billion samples going in, there shouldn't really be repitions
> visible, unless your data is repetitive.
> 
>>>> Is there some correlation between data rate on the record and
>>>> FFT refresh rate?
> No. Refresh rate is just the display refresh rate, i.e. the speed
> at which the GUI updates its visualization.
> 
>>>> How is 'FFT Size' used (right now I have that at '1024')?
> Um this is kinda awkward - it's the size of the FFT; how the
> samples are internally processed prior to being transformed depends
> on the actual FFT sink implementation.
> 
>>>> On a related note - is there a way to get the FFT to start
>>>> out in 'Autoscale', or do I need to hit the button every
>>>> time?
> 
> No. "Autoscale" is (as far as I know and can remember right now)
> not a /mode/ for the qt nor the wx gui fft sink, but scales the
> display to fit the data that is display /the moment the button is
> clicked/. So, since data can only be available at run time, you
> can't do that before running the flow graph. However, at least for
> the qt implementation, you can set y max/y min, if you know it
> beforehand.
> 
> So: Verify your data is really about 1 billion samples long and
> not only a few thousand; if your waterfall looks periodic, your
> recorded signal is periodic.
> 
> Greetings, Marcus
> 
> On 03.12.2013 22:45, Paul B. Huter wrote:
>>>> 
>>>> Is there some correlation between data rate on the record and
>>>> FFT refresh rate? How is 'FFT Size' used (right now I have
>>>> that at '1024')? On a related note - is there a way to get
>>>> the FFT to start out in 'Autoscale', or do I need to hit the
>>>> button every time?
>>>> 
>>>> Thanks!
>>>> 
>>>> 
>>>> On Tue, Dec 3, 2013 at 3:01 PM, Marcus Müller
>>>> <address@hidden> wrote:
>>>> 
>>>> Most probably your data is simply to short in relation to the
>>>> fft length and the amount of samples your specific graphical
>>>> FFT amplitude sink drops for display. Please review you fft
>>>> length, update rate, and try out different fft GUIs (qt/wx).
>>>> 
>>>> You could zeropad your data generously to notice the
>>>> repitition. However, I think with what you're describing you
>>>> might be better off with a waterfall graph; try them, they're
>>>> fun :)
>>>> 
>>>> Greetings, Marcus
>>>> 
>>>> On 03.12.2013 21:45, Paul B. Huter wrote:
>>>>>>> When I play my data file back through a throttle and 
>>>>>>> frequency translating FIR filter to an FFT sink with
>>>>>>> repeat OFF, it seems to just show a static plot.
>>>>>>> However, with repeat ON, I get playback, but I can't
>>>>>>> tell when data ends and starts back over. Is there a
>>>>>>> way for me to know when it repeats? Or, is there a way
>>>>>>> to get playback with repeat turned off?
>>>>>>> 
>>>>>>> Thanks.
>>>>>>> 
>>>>>>> Paul B. Huter
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> _______________________________________________ 
>>>>>>> Discuss-gnuradio mailing list address@hidden 
>>>>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>>>>>
>>>>>
>>>>>
>>>>>>> 
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>>>> 
>> 
> 
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