One of the powers or Unix (Linux) is that you can 'pipe' signals from one program to the other (and that also works via the internet with netcat).
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While testing the spectrum analyzer I am writing, with its build in radio receiver facility, I got a bit irritated by people not having sufficient modulation (some do not know how t use a microphone). Long time ago I wrote xpequ,
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and yes it can read from stdin and write to stdout. Linux 'play' (= sox) can do companding. xpsa can get the station from the spectrum, 'rtl_fm' to receive the narrow band FM signal and demodulate it, 'xpequ' to apply a graphic equalizer to get only speech related audio (less noise), 'xpequ' to do audio AGC (keep level constant, compensate for microphone misuse), 'xpequ' to show the audio FFT, you can select scope mode too, 'play' to compand the signal and play it via the audio device and speaker. 'xpequ' can drive the room LEDs too :-)
The long green line shows the command line executed by xpsa.... That will be in version release 0.6..