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Do you have details on the encoding? I'm a bit suspicious of it being actually ultrasonic (device microphones often filter at 20khz or below) - seems more likely it would be audible spectrum noise with a ton of FEC.

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I can't speak for SilverPush, but Google Tone definitely has an Ultrasonic component [1] as does a version of Chirp [2]. Both work through consumer grade speakers/DACs/devices.

[1] https://www.reddit.com/r/AskEngineers/comments/374876/lets_t... [2] https://vimeo.com/177586203

They map each letter (A-Z) to a single frequency. The range is around 18-19.5 kHz. As far as I know, this range is inaudible to most adults. I couldn't hear it for example. Of course, I may be using the term ultrasonic incorrectly.

Some preliminary work was done last year to reverse SilverPush[1], but my group and I are planning to take it further.

[1]: https://github.com/MAVProxyUser/SilverPushUnmasked

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