Inaudible audio tracking is IMO almost always against users informed consent, so apps doing it should be suspected as malware.
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Replying to @halvarflake
TVs & other devices that play audio should also be actively protecting privacy by filtering this content to prevent reception.
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Replying to @RichFelker @halvarflake
how can a TV filter hidden signal in audio? it's not like you need ultrasound/... to hide a message in sound
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Replying to @tehjh @halvarflake
Roughly speaking, by applying its own random signal modulated the same way the hidden tracking signal is modulated.
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Replying to @RichFelker @halvarflake
if you don't know the encoding, you'll afaik need way more noise than the tracking signal itself, right?
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since otherwise the encoding can average out the noise while adding up the signal?
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and the ad creator has the advantage of being able to modify individual components of the signal
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and the TV needs to operate in realtime, the attacker doesn't
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and for ads, if nothing else works, you can manually create 2 variants each in N places and get 2^N combinations
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(with the disadvantage that you then have to ship information about individual ads to phones)
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