Re: [Discuss-gnuradio] Resampling rate method assistance

[CEL]

Hi Carlo!

On Wed, 2018-05-30 at 23:04 +1000, Carlo Manfredini wrote:
> My hardware arrangement is fairly demanding, I think ?
> I wish to resample between a Red Pitaya connected via ethernet running at 
> 100kSps and a USB-audio unit (UCA-202) running at 48kSps.

That's not "much signal to process"! In the context of SDR, we're often
considering dozens of Megasamples per seconds.

> This code is simply a "loopback test" for both units running at once.

Ha, I think that's the point here.
So, this sounds like the good ole' two-clock-problem: The rate of your
sound card is slightly different from 48 kHz, and the rate of your
Pitaya. But you do a perfect adaptation between 100 and 48 kHz. So, at
the end, one device has too many or the other too little samples per
second.

> I would then add some signal processing to the signals in and out once I have 
> these working correctly.
> You can also see the break in the audio signal display in the time sink...as 
> well as the aUaUaU...
> When I view the PCs system monitor, it is using about 50% resources.

> Perhaps the USB-based audio device is struggling to operate continuously 
> given that the RP is communicating via ethernet at about 1000kBps (according 
> to System Monitor).

That's not really that much data, and you properly decimate that to the
rate your sound card can nominally do!

> USB devices tend to be "bursty" and rarely operate continuously without 
> breaks when the PC has other tasks to attend to.

Yeah, and something along these lines occasionally happens, because
talking to drivers is hard and GNU Radio's audio sink doesn't do that
in the best possible way, but really, the USB granularity doesn't lead
to discontinuities anywhere else, so why should it here?

> A screenshot of the code is: 
> https://drive.google.com/open?id=1XTNlHB87kNrX82cItMPWMvLGCGXvyr0U
> Thanks for any further suggestions.
> Maybe an option is to run the USB device at a slower sample rate ?

Really, the amount of data isn't much here. You can use your system
monitor to see how much your CPU is utilized. It should be... limited.


Best regards,
Marcus

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