Hello
There are numerous devices that transmit audio via very low frequency (VLF). I quote:
"Carrier current devices are a combination of technologies. They are a cross between
wired microphones and subcarrier transmitters. The only difference is that the signal
is not transmitted via radio waves, but rather through a wire pair. A person cannot
accidentally intercept or detect a carrier current signal by simply tapping into a wire
like with wired microphones. A carrier current device works by picking up room audio
through a microphone. The signal from the microphone is then modulated by a low
frequency circuit, which produces a carrier current signal at approximately 100–200
kHz. A common example of carrier current devices are the newer wireless telephones,
intercoms, or baby monitor type devices that plug into the electric socket and use the
pre-existing wiring rather than having wiring run all over the house. A special circuit,
which can demodulate the low frequency signal, is used as the receiver.
Only a sophisticated receiver with a low frequency probe can detect this sort of device."
Can Audition modulate the signal back into an audible range?