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What frequency are these apps using? I haven't looked it up but I doubt most computer speakers go above 15Khz (why would they?) A young person should be able to

by gmarx 10y ago

What frequency are these apps using? I haven't looked it up but I doubt most computer speakers go above 15Khz (why would they?) A young person should be able to hear really high but audible tones and an adult would rapidly lose the ability. If this is not the case it would make sense to set a limit on the tones such a device can send and receive. On the other hand there might be legitimate uses for such tech so maybe better to have it as a security option to send and receive ultrasound per individual, i.e. if I can't hear above 10khz maybe I can set my audio to not send or receive above that without app specific permission

anshumanf 10y ago
From some quick digging I did in a Github repo attempting to reverse-engineer the 'audio beacons', the frequencies used by at least one startup using the technique are in the 18kHz range[1]. https://github.com/MAVProxyUser/SilverPushUnmasked/commit/bc1dde934c0be02cfce72b7ea68d4a147ddd308d https://github.com/MAVProxyUser/SilverPushUnmasked/commit/bc...
ChartsNGraffs 10y ago
Things like Apple TV/Chromecast are serving ads and are hooked up to audio systems that are usually quite capable. And this could easily just shift to being done within the range of computer speaker production/human hearing and it would sound like a glitch at best (if audible at all).
brian-armstrong 10y ago
It's not exactly that straightforward. In general any modern audio equipment will run up to 20kHz since that's generally accepted as the range of human hearing. From what I can tell, the lowpass filters built in to equipment (eg antialiasing on ADC/DAC) attenuates starting at 19 or 20 kHz. But these are realized as low order physical filters, meaning they roll off slowly, so you'd have to start attenuating at something much lower to truly remove the 18-20 range. That would introduce distortion where the rolloff starts, which you probably don't want.

by gmarx 10y ago

anshumanf 10y ago

From some quick digging I did in a Github repo attempting to reverse-engineer the 'audio beacons', the frequencies used by at least one startup using the technique are in the 18kHz range[1]. https://github.com/MAVProxyUser/SilverPushUnmasked/commit/bc1dde934c0be02cfce72b7ea68d4a147ddd308d https://github.com/MAVProxyUser/SilverPushUnmasked/commit/bc...

ChartsNGraffs 10y ago

Things like Apple TV/Chromecast are serving ads and are hooked up to audio systems that are usually quite capable. And this could easily just shift to being done within the range of computer speaker production/human hearing and it would sound like a glitch at best (if audible at all).

brian-armstrong 10y ago

It's not exactly that straightforward. In general any modern audio equipment will run up to 20kHz since that's generally accepted as the range of human hearing. From what I can tell, the lowpass filters built in to equipment (eg antialiasing on ADC/DAC) attenuates starting at 19 or 20 kHz. But these are realized as low order physical filters, meaning they roll off slowly, so you'd have to start attenuating at something much lower to truly remove the 18-20 range. That would introduce distortion where the rolloff starts, which you probably don't want.