Sonic shenanigans

This Place Is Dead linked to this incredible-sounding story:

A yob-busting alarm using ultra high sound to drive teenage thugs from shopping centres has been hijacked to create inaudible classroom ringtones.Techno-savvy school kids are getting away with using mobile phones in class through the creation of ringtones adults cannot hear.

British firm Compound Security has been praised by the police for its Mosquito device which was developed to stop teenage gangs hanging around outside shops.

Once installed on a building, it emits a high-pitched sound, like a constant insect buzzing, to drive the problem away.

It is highly effective because it cannot be heard by most people over the age of 20 but is deeply irritating to teenagers.

Now the youngsters have turned the tables by making high-pitched recordings which allow them to exchange text messages in class unheard.

Known as “Teen Buzz”, it is spread from phone to phone via text message and blue tooth technology.

I call shenanigans. It’s easy to create a tone of a specified frequency in any audio editor, and I can happily hear 15Khz, 17.5KHz and 20KHz tones (20KHz is the usual upper limit of human hearing) despite my advanced age (33), several years of iPod abuse and 16 years of playing extremely loud guitars in various rock bands. I can also hear Teen Buzz fine, despite its frequency of 18 and a bit KHz. That puts it well within most people’s hearing range – but well outside the typical frequency range attainable with mobile phone loudspeakers, which struggle with frequencies above 10KHz.





0 responses to “Sonic shenanigans”

  1. One does doubt that mobile phone speakers could easily reproduce such high-pitched sounds. But I do remember that when I was a kid I could hear a high-pitched tone coming from the TV, that I stopped hearing as I got older.

  2. I still hear that tone from TVs.

  3. Gary

    Is that the high-pitched whine you get from CRTs? If it is, I can hear it too. Not now, obviously, but when I’m near one :)

  4. For me, it’s so clear that I can tell when a TV’s on in the next room with the sound down, but I’ve met quite a few people who can’t hear it, who are so convinced that the noise isn’t there, in fact, that they accuse me of lying about it. If this ringtone thing were real, pupils would have to rely on having such people as their teachers. Bit of a gamble.

  5. Hmm, I’m a bit disappointed to discover more physical signs of ageing! Although I am a wee bit older than you guys anyway!

    And on the ringtone thing: if you can’t hear it does that mean you also can’t see someone obviously concentrating on something they are holding out of sight? If not, it doesn’t strike me as a huge blow against classroom discipline.

  6. The big blows against classroom discipline are parents who back their kids up no matter what and educationalists who introduce policies aimed at not hurting children’s feelings rather than at teaching them. Anything else is just the result.

    My mother-in-law says they’re no longer allowed to mark their pupil’s work in a different coloured ink from what the pupil used. To do so would reinforce the idea that the teacher is different to them; it’s too confrontational. Neither are they allowed to put long comments on the work: just a “right” or “wrong” is considered sufficient (although “wrong” is being phased out in smoe jurisdictions — hello, Scotland). Shout at a child and they’ll have you up on “human rights abuses”. And, of course, you can’t go confiscating a kid’s mobile phone without their parents going through the roof and accusing you of theft.

    She’s glad she’s retiring.

  7. david

    >>Is that the high-pitched whine you get from CRTs?

    If its audible to most people then the refresh rate is too high for the monitor.

    Jo – did you not say that you have difficulty tuning noises out sometimes or did I totally make that up?

    I don’t conciously hear the noise that TV tubes make by I am conscious of its absence so I suppose I can hear it.

  8. I have no idea whether I ever told you that, but it is true. I can’t ignore noises. They demand my attention.