Quiet

Documentation

This library uses liquid SDR to transmit data through sound. This makes it suitable for sending data across a 3.5mm headphone jack or via speaker and mic. Quiet can build standalone binaries for encoding/decoding data via .wav files or for streaming through your soundcard via PortAudio. It can also be built as a library to be consumed by other C programs.

Build

With the dependencies installed, run ./bootstrap provided by this library, which will create a build directory and invoke cmake. If you would like to install it after building, do cd build && make install.

Profiles

The encoding and decoding processes are controlled by the profiles in quiet-profiles.json. Each profile contains a complete set of parameters such as modem type and error correction.

Cable

For cable transmission, use the cable- profiles. These will attempt to use nearly the full spectrum provided by your soundcard. As such, they contain many audible frequencies and should not be used on channels that could be heard by people.

Ultrasonic

The ultrasonic- profiles encode data through a very low bitrate, but the audio content lies above 16kHz, which should pass through audio equipment relatively well while being inaudible to the average person. This is a good option for sending data through a channel where you would prefer not to disrupt human listeners.

Dependencies

Liquid DSP Be sure to work from the devel branch
libfec (optional but strongly recommended)
Jansson
libsndfile (optional)
PortAudio (optional)

Acknowledgements

I'd like to thank the people who provided feedback and helped me with pull requests and advice on software

Joseph Gaeddert, for his excellent SDR library, encouragement, and feedback on all things DSP
Alon Zakai and @juj for advising me on emscripten and for taking my PRs
Jan-Ivar Bruaroey and Maire Reavy for helping me patch the echo cancellation behavior of Firefox's getUserMedia
Josh Gao for advising me on API design and C idioms.
Ryan Hitchman for extensive testing on Android Chrome
Fabrice Bellard for thoughtfully answering a stranger's question out of the blue about digital communications