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Digitally Colourful Mistifier

SDR Noob alert: choppy audio output

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Hi, I just got started with the HackRF One and it's really fun. I'm following the lessons at greatscottgadgets.com but with lesson 1 I'm already facing some issues I just can't seem to get solved on my own. The problem I'm facing is the classical 'choppy output' of the audio when demodulating FM radio. The schema that we're supposed to build is explained in great detail at https://greatscottgadgets.com/sdr/1/. I followed all the steps, I think my schema is exactly as what he told me to build, but still I'm getting choppy output, for as far as my googling learned me anything this means that I've messed up the sample rates at some point. It's not that my hardware can't keep up with the rate, already checked that by lowering the rate to ridiculously low levels but that didn't help to solve the choppy output. Anyone having some hints for me? I've included a screenshot of my workflow:

yMaXZ4X.jpg

My setup looks like this:

- Physical machine is a recent macbook pro with 8GB RAM and 4 cpu-cores running OSX Sierra

- Virtual Machine is a Debian 9 with 3GB RAM and 1 cpu-core

 

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Have you tried doing this on a bare metal box? Digital Signal Processing for both the SDR and Audio Out can get messed up through visualization. 

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Correct, that was the answer. When playing with SDR on a VM you can get messed up results. This is caused by the virtualisation layer, it slows down a whole number of things including USB-connections and audio-output. It was the latter which caused the error  in my case. I discoverd I could fidle a little bit with the output sample rate (make it a little higher than 48Khz) which solved the audio-underrun problem, but which then in effect caused CPU-overrun :-). So yes, the solution to my problem was installation on a bare metal box.

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On 11/6/2017 at 12:58 AM, Digitally Colourful Mistifier said:

Correct, that was the answer. When playing with SDR on a VM you can get messed up results. This is caused by the virtualisation layer, it slows down a whole number of things including USB-connections and audio-output. It was the latter which caused the error  in my case. I discoverd I could fidle a little bit with the output sample rate (make it a little higher than 48Khz) which solved the audio-underrun problem, but which then in effect caused CPU-overrun :-). So yes, the solution to my problem was installation on a bare metal box.

Woo! Glad it worked out!

Hey If you want to run a virtual instance effectively with SDR I would recommend looking for a type 1 hypervisor like xen. VM's will run threw the hardware instead of the host operating system meaning faster IO for the SDR. 

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