5 ms·

I'm not even sure if there's a car audio system that could reproduce that range.

• jacquesm 4y ago
  It's just DTMF I don't see why not. The base frequencies are all around the 1 KHz band which even the most boneheaded amp + speaker implementation should be able to reproduce.
  • throwanem 4y ago
    I think the question is whether a car stereo could reproduce the so-called "brown note", which as I recall is supposedly somewhere around 12Hz. SAME BFSK uses frequencies iirc between 1 and 2 kHz, and the attention signal is an equal mix of 853 and 960 hertz.
    • jacquesm 4y ago
      Ah yes, you are right. Indeed, that's way lower than any stereo other than the weird ones that some kids build into the backs of their cars (note to self: do not lend your car out to junior employees that like subsonics, hi R. I know you're reading HN). Besides that, those would be filtered out on the transmitter end long before they were allowed to modulate the signal. Especially AM transmitters may do some pretty wild stuff when you drive them with frequencies that low, fair chance that you'll find that you hold them 'on' long enough that you're going to find the limits of either the power supply or the cooling system. Both on the high end (5KHz and up in theory, but more like 3KHz in practice) and on the low end (100Hz in theory, but you can go as low as 50 Hz in practice). So I highly doubt that story is true.