Show HN: MT63 digital radio transmitter and receiver in WebAssembly

We're working on sonifying the signed timestamps for QR Date (https://news.ycombinator.com/item?id=30566037) that can be played back without the QR code being in-frame for video. Having the timestamp played back through a speaker while filming also imprints its own convolution with the space you're in, so the audio is extremely hard to fake convincingly. We ended with using MT63 modulation to encode the returned URL, and fixing this library originally by KD7BBC up for easier re-use by others.

The result is already working as an API endpoint running on AWS Lambda: https://qrdate.org/api/datemt63 (noise warning!)

If you feed the signal through fldigi or similar in MT63 2000L mode with a center frequency of 2000Hz, the qrdate.org verification URL should show up. I also tested out how it might work through several layers of twitter compression today: https://twitter.com/miuott/status/1501490321670217731

If anyone has any idea where the original source for Pawel's implementation for MT63 is, please let me know. As it's supposedly public domain, we'd like to eventually break off with another non-GPL license that was not applied by fldigi so that an MT63 implementation could be put up on the App Store. Rewriting the library entirely is a big task as there's some serious DSP magic in there.