ChirpChirp is a script to transmit data over audio with chirp modulation.
ChirpChirp requires Python, Numpy, PortAudio, and PyAudio.
To install these on a Debian GNU/Linux system:
$ sudo apt-get install python python-numpy python-pyaudio
First choose a chirp, which is determined by its bounding frequencies and period (duration). For example, frequencies of 2 to 12 kHz, and a period of one eighth of a second, are a good choice.
Then start a receiving process in one terminal:
$ python -u chirpchirp.py rx 2000 12000 0.125
and a transmitting process in another terminal, with the same parameters:
$ echo Hello | python -u chirpchirp.py tx 2000 12000 0.125