[bcheung]

A lot of fingerprinting technologies use something called Difference of Gaussian (a type of bandpass filter). However, in practice you capture interest points across multiple bands (scale space).

Basically what this means is that interest points are in multiple frequency bands.

A high or low pass filter is unlikely to filter out a significant number of these interest points at other frequencies so the fingerprint is still able to match with a fairly high confidence.

[luddaite]

If the fingerprint frequencies are in the audible range, wouldn't you hear a brief humming when the fingerprint signal is being broadcast?