TIP -- Cleaning Up SDR Audio In Linux

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wb6apx

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Dec 12, 2015
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Grants Pass, OR
Traditionally, the audio from SDR-RTL dongles isn't the best -- whether it is from the hardware itself, weak audio processing by rtl_fm, or other causes.

I've come up with a simple, yet elegant, command line which will run rtl_fm and scrub the audio to the point where it sounds like many of the high end scanner radios -- or better.

Here is my command line:

Code:
sudo rtl_fm -E deemp -E dc -F9 -l $1 -M fm -s 12k  -f 159.27000M | sox --buffer 128 -t raw -r 12k -es -b 16 -c 1 - -p sinc 200-3.5k compand 0.1,0.8 6:0,-3 | tee >(sox -p scan_out.wav) | play --buffer 128 -p
First, rtl_fm is run with the proper options. That is then piped through sox, using a buffer and the proper filters to "massage" the audio and remove undesirable sounds. Finally, the cleaned up audio is piped to sox's play utility.

This works on both fm and am modulations -- and it sounds great!
 
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