3 ms·
The acoustic modem is back in style [1]! And, of course, same frequencies (DTMF) [2], too! DTMF has a special place in the phone signal chain (signal at these
by nomel 2y ago
The acoustic modem is back in style [1]! And, of course, same frequencies (DTMF) [2], too!
DTMF has a special place in the phone signal chain (signal at these frequencies must be preserved, end to end, for dialing and menu selection), but I wonder if there's something more efficient, using the "full" voice spectrum, with the various vocoders [3] in mind? Although, it would be much crepier than hearing some tones.
[1] Touch tone based data communication, 1979: https://www.tinaja.com/ebooks/tvtcb.pdf https://www.tinaja.com/ebooks/tvtcb.pdf
[2] touch tone frequency mapping: https://en.wikipedia.org/wiki/DTMF https://en.wikipedia.org/wiki/DTMF
[3] optimized encoders/decoders for human speech: https://vocal.com/voip/voip-vocoders/ https://vocal.com/voip/voip-vocoders/
- bigiain 2y agoI'm wondering if shifting frequency chirps like LORA uses would work in audio frequencies? You might be able to get the same sort of ability to grab usable signal at many db below the noise, and be able to send data over normal talking/music audio without it being obvious you're doing so. (I wanted to say "undetectably", but it'd end up showing up fairly obviously to anyone looking for it. Or to Aphex Twin if he saw it in his Windowlicker software...)
- nomel 2y agoThe issue is the (many) vocoders along the chain remove anything that don't match the vocal patterns of a human. When you say hello, it's encoded phonetically to a very low bitrate. Noise, or anything outside what a human vocal cord can do, is aggressively filtered or encoded as vocal sounding things. Except for DTMF, which must be preserved for backwards compatibility. That's why I say it would be creepy to do something higher bitrate...your data stream would literally and necessarily be human vocal sounds!
- _def 2y agoData exfiltration via bird
- westurner 2y ago"Using the Web Audio API to Make a Modem" (2017) https://news.ycombinator.com/item?id=15471723 https://news.ycombinator.com/item?id=15471723
- genewitch 2y agoYes. JT8 / FT8, wspr, and then the entirety of fldigi. To get started. If you need more speed you need to convince me you won't abuse my ham spectrum but winlink, pactor, and some very slick 16QAM modems exist. 300baud to 128kbit or so.
- pjc50 2y ago> it would be much crepier than hearing some tones. Hatsune Miku at the speed of a horserace commentator. (the "vocaloids" are DAW plugins made from chopped up recorded phonemes; Hatsune Miku is voiced by Saki Fujita. Still sounds very inhuman)
- Gracana 2y agoThis isn't DTMF. It's a form of MFSK like DTMF, but it operates on different frequencies and uses six tones at once vs DTMF's two.