• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:

TIP -- Cleaning Up SDR Audio In Linux

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Dec 12, 2015
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:

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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