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link: Chromecast Now Lets Your Guests Take Over Your TV Without Needing Your WiFi Password
Back in June, Google announced a rather nifty new feature coming to Chromecast: your friends and house guests would soon be able to connect to your Chromecast without being on your WiFi network, thanks to the clever use of magic ultrasonic sounds.
after a few months of silence, that feature launches.
One bummer of a caveat, though: it’ll only work if your friend’s phone is running Android, for now. Why? It all comes down to that age-old problem: iOS apps aren’t allowed to do certain things required to make it work, so they’re rolling with it on Android until that changes.
Guest mode is off by default. Flip it on, and your Chromecast will start displaying a PIN on its idle screen. Meanwhile, your TV will start emitting ultrasonic sounds, inaudible to the human ear*, which Chromecast-enabled apps on your phone will be listening for. When the two find each other, everything falls into place and the pairing is made.
[* No word yet on if non-human ears (i.e. dogs) can hear it. If your dog starts whining whenever your Chromecast is on, you should probably turn guest mode back off.]
(Score: 2) by SlimmPickens on Friday December 19 2014, @04:28AM
How do they do that?
Because usually parts of the playback chain (speakers and sound cards) have filters to throw away inaudible frequencies. I assume TV's do this too, plus it has to work with crappy equipment.
According to this [stackexchange.com] one sample in a 44100 Hz stream is supposedly audible as a click (0,0227 ms). I remember a larger number being mentioned in my favorite synth book, but am so far unable to find it.
(Score: 2) by frojack on Friday December 19 2014, @06:18AM
In my youth I could hear some really high pitched sounds.
Not any more. (remember the mosquito ring tone? I couldn't hear that when it became popular).
These days they could be clicking all day long at that frequency and I wouldn't hear a thing.
No, you are mistaken. I've always had this sig.
(Score: 2) by Bot on Friday December 19 2014, @06:48AM
I would add, why do they do that? a low baud, audible pairing would be magic.
After all, magic is what you're not accustomed to.
in 1985 the idea of reading a disc with laser was magic, today reading audio with a needle on a groove is magic.
Account abandoned.
(Score: -1, Redundant) by Anonymous Coward on Friday December 19 2014, @10:58AM
...The best of both worlds....
Play vinyl records like CDs -- NO MORE WEAR AND TEAR ON THE RECORD GROVES!
http://www.elpj.com/ [elpj.com]
TL; DR:
Last time I checked:
The laser turntables were EXPENSIVE!!!
The laser turntables only play black vinyl records.
The laser turntables can play broken/badly warped records that are impossible to play on normal needle-based turntables.
The president/CEO of the company spared no expense to preserve analog audio as is for current and future generations of listeners as examples of culture and history.
(Score: 2) by cafebabe on Saturday December 20 2014, @07:39PM
I heard of a device which was available in Hong Kong more than 10 years ago which used lasers to play almost any type of disk: vinyl, CD, Video CD, Laserdisc. I presume it wasn't widely available due to borrowed code and unlicensed codecs.
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(Score: 0) by Anonymous Coward on Saturday December 20 2014, @03:49AM
After all, magic is what you're not accustomed to.
in 1985 the idea of reading a disc with laser was magic, today reading audio with a needle on a groove is magic.
How so? One of the first music CDs came out in 1981. Also, the first commercial LaserDiscs came out in 1978. If in 1985 you though it was magic then you must have been a backwoods rube.
(Score: 4, Informative) by Foobar Bazbot on Friday December 19 2014, @06:50AM
Your one-sample "click" is an approximation of an impulse. An impulse, as any schoolboy knows, contains power at all frequencies, so it should be unsurprising that a finite approximation includes some audible ones -- it doesn't follow that a train of such pulses (i.e. a 22.05kHz square wave) will also be audible. (To be exact, a single-sample click is best modeled as a rect function, whose fourier transform is the sinc function, but it doesn't change the conclusion.)
Anyway, the thing is, you really don't want to discard audible content, and there are no ideal (brick-wall) low-pass filters, so the filters that "throw away inaudible frequencies" necessarily leave a substantial amount of near-audible ultrasound.
(Score: 0) by Anonymous Coward on Friday December 19 2014, @12:03PM
As I understand it, the TV needs to be built specifically for this system anyway, so I'd expect those TVs also to be built to be able to emit those high-frequency sounds. Probably they are added in after the TV sound passed those filters (after all, you don't want high frequencies in the TV sound to disturb your intentional ultrasound signal), and the speakers are built to handle those. Alternatively, the TV could get a small extra speaker specifically for the ultrasound. Note that due to the high frequency, ultrasound speakers may be quite small.
If the TV has also a microphone built in, I could also imagine that the TV could be hacked to use this ultrasound emission as surveillance device (remember, bats use ultrasound to "see" their surroundings; there's no reason a TV with ultrasound emission capability shouldn't be able to do that, too).
(Score: 2) by cafebabe on Saturday December 20 2014, @07:50PM
Echo-location with a single microphone is a fanciful element of a Batman film (The Dark Knight Rises?). Regardless, a single microphone in a telephone or television is ideal for surveillance, even if it sampled at a low frequency.
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