Simply listen to an FM broadcast station using RTL-SDR


Building on my previous post of listening to radio by re-streaming it as a compressed stream, here is a simpler way of encoding the audio straight to your computer’s speakers”

You’ll need to install ‘RTL-SDR’ (as before) and also ‘sox’.

From Ubuntu and similar linux distros, the command is:

sudo apt-get install sox

For Apple Mac install MacPorts (or Brew, another popular Mac installer) then:
Macports:
sudo port install rtl-sdr sox
Brew:
brew install rtl-sdr sox

…or if you already have rtl-sdr for use in my previous post, simply use:
Macports:
sudo port install sox
Brew:
brew install sox

Once installed, listen to BBC Radio 4 in Brighton on 94.5 MHz (or change to your favourite local station!) by using this command:

rtl_fm -f 94.5M -M fm -s 170k -A fast -l 0 -E deemp | play -r 170k -t raw -e s -b 16 -c 1 -V1 -

RTL_FM receives the radio as before, and play (part of sox) uses these parameters:

-r 170k <= This tells sox to receive the stream from RTL_FM at 170Kbps, matching RTL_FM’s -s 170k bandwidth parameter.
-t raw <= This denotes a raw input stream, not a file
-e  s <= encoding; in this case ‘s’ for ‘signed integer’, part of the raw stream.
-b 16 <= Number of bits in each audio sample
-c 1 <= a single audio channel (not stereo, because RTL_FM does not decode stereo FM signals)
-V1 <= ‘verbosity level’ – causes sox to display details about playback
  – <= Read the stream from stdin (piped from RTL_FM’s stdout using the vertical | symbol).