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04-14-2018, 03:41 PM
(This post was last modified: 04-14-2018, 03:41 PM by Michaela Joy.)
I remember reading about this technology years ago. IIRC, it used an ultrasonic "tag" to tie a cellular phone to a computer at a specific location.
That was before IPv6 was popularized. IP4 is just too generalized to pin someone down to a specific city block, much less a geo-location.
The biggest problem was the Nyquist limit of most sound cards at that time. Back then, 44.1 khz was the default for most sound cards. that sets the nyquist limit at 22.05 khz.
Trying to use ultrasonics would create aliases folding over into the audio range of the sound card.
These days, just about every sound card comes stock set to 48 khz (as opposed to 44.1 khz) That would set the nyquist limit at 24 khz.
If you used narrow-band FSK, I bet hardly anybody would know it was there.
FSK: https://en.wikipedia.org/wiki/Frequency-shift_keying
Nyquist Frequency: https://en.wikipedia.org/wiki/Nyquist_frequency
That was before IPv6 was popularized. IP4 is just too generalized to pin someone down to a specific city block, much less a geo-location.
The biggest problem was the Nyquist limit of most sound cards at that time. Back then, 44.1 khz was the default for most sound cards. that sets the nyquist limit at 22.05 khz.
Trying to use ultrasonics would create aliases folding over into the audio range of the sound card.
These days, just about every sound card comes stock set to 48 khz (as opposed to 44.1 khz) That would set the nyquist limit at 24 khz.
If you used narrow-band FSK, I bet hardly anybody would know it was there.
FSK: https://en.wikipedia.org/wiki/Frequency-shift_keying
Nyquist Frequency: https://en.wikipedia.org/wiki/Nyquist_frequency
