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The Sound of Safety?
Nostrada writes: "Gone are the days of mobile phones ringing with the latest and greatest melodies? Following this article, "A new sound that could revolutionise mobile telephones and safety alarms because it is less intrusive yet easy to pinpoint is being ordered worldwide after being developed by a British scientist." Anyone got some URLs for samples?"
"It initiates a reaction that makes you instantly turn towards that sound"
This sound will also be heard before TV commercials, radio commercials, it will replace the windows startup sound, and children will learn to make it when they want something or want to annoy you. Not a nice thing to grace the earth with.
White noise has a linear spectral power density, Pink noise has a logrithmic spectral power density.
White noise has the same power density from 100-200 HZ as it does from 1100-1200 HZ or any other 100 HZ segment.
Pink noise has the same power density from 100-200 Hz as it does from 1000-2000Hz or any other 2:1 octave ratio.
Here are some .AU files that are supposedly examples of the use of this Localizer sound in sirens for emergency vehicles.
http://www.premierhazard.co.uk/sirentnj.html
has anyone figured out how to reproduce this sound? i'm sure that if it's just white noise then any PC could be coaxed into mixing this sound with a more pleasing sound (instead of Localizer+Siren) to get your attention for things like chat messages and alerts (would be great in a NOC environment)
I heard them talking about this on CBC (Canadian national radio) a year ago. They were talking about the practical uses on ambulances and other emergency vehicles. Apparently tests in the UK had shown that emergency vehicles equiped with one of these new sirens could get to their destination faster (people knew where the sound was coming from and were better at getting out the way), and the number of secondary accidents was reduced (people crashing whilst looking for the emergency vehicle, etc).
Ironicaly, for safety reasons introduction in to Canada (and the US???) will be delayed as there are strict guidelines and tests to meet for new sirens.
Okay, so you've got a fire engine going down the street, making a noise that makes everyone turn and look at it. As we know for driving school, when you look somewhere, you tend to drive that way. So we'd have all of these distracted drivers crashing into emergency vehicles. Great...
I saw a bit on some police camera show on TLC about a similar sound being tested by some police force in Britain. Apparently the sound is easier for people to locate, allowing drivers to get out of the way of emergency services vehicles safely. Get the ambulance, fire truck, etc. to the scene faster, lives are bound to be saved. You're also less likely to have accidents as people panic from the police car pulling up behind them "without warning" (because they couldn't tell where it was and so weren't expecting it).
;-) But the same idea - broadband white noise in whooshing patterns in between siren bursts.
The show was first run months ago, but it was just re-run lately. Same sound? Can't tell.
I'm surprised your friends haven't started carrying around mallets in case your phone rings. That, or like firemen, they associate the song with the video and get excited?
--
"The urge to save humanity is almost always a false front for the urge to rule." --H.L. Mencken
Not too great on IE 5.0 when you don't let them "upgrade" Media Player to the newer, more evil version. After I set the preferences for audio only (don't want the sales pitch, just want to hear what the sound sounds like) I got a still picture and then it crashed IE. Or gave IE an excuse to self-destruct. :-)
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Kate Bush? That *was* years ago.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
I just tried the PremierHazard link from post #79. What this sounds like is a siren run through an amp that's intermittent at about a 3 or 4 Hz rate. Think of a siren interspersed with the "microphone keying" burst of static which television has trained us to associate with police 2-way radios. It's very annoying, but doesn't seem any more directional than the siren itself. The directional cues probably come as much from the interruption of the siren by the noise (and then the noise by the siren) as from the noise itself.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Yeah, well that and the fact that in the unlikely event that any of the sound of the siren got through their rolled up windows, blasting stereos, and roaring air conditioners, they couldn't be bothered to turn down the radio, roll down the window, start slowing down just in case, and look around, including checking their rear-view mirrors.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
It's been years and years so I forget which is which, but one of them, as I recall, is equal energy per frequency division (for example, just as much from 1.597kHz to 2.597kHz as from 206.0312kHz to 207.0312kHz), and the other is equal energy per octave (just as much from 110Hz to 220Hz as from 220Hz to 440Hz as from 440Hz to 880Hz). If I further remember correctly the octaves had to be related, that is, the same energy in the 110Hz to 220Hz band as in the 370Hz to 740Hz band didn't count.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
One of the licensees of the SoundAlert tones is Permier Hazard. They have a Sirens page that has several example files in .au format
http://www.premierhazard.co.uk/siren.html
A sidenote. I read something about a year ago, but I just can't recall where. (I'll keep Googling, but I think I read it in Scientific American or something.) A fire department tested out one of these new sirens, and they worked splendidly in all the important ways...but one. Traffic could easily determine where the fire engine was coming from, the siren was easily heard, and that was all nice. The problem was that firemen have learned to associate the sound of the engine with excitement. So they arrived at fires unprepared, psychologically, and without the gusto to fight the fire. Weird, huh?
-Waldo
(And I thought my Nokia singing "Oops, I did it again" every time I get a call was bad enough...)
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When the useless car alarms copy this,
then everyone will ignore it.
"What I have done is simple: I select noises for electronic engineers, which I know the human brain will recognise and interpret within milliseconds. They then convert them into electronic noises, which, according to need, are variations on chusssh-chusssh-chusssh."
Recognize and interpret within milliseconds...
I don't know about the rest of you but "chusssh-chusssh-chusssh" is not a sound I hear often in my daily life.
I know what you are thinking, I must not be getting enough "chusssh" in my life.
Well I am getting enough "chusssh" and when I have "chusssh" it does not sound like "chusssh".
(It sounds much more like pr0n...)
Try to hack my 31337 firewall!
They have already developed a similar (though somewhat less violent) thing... it's called vibrate mode. I leave my phone on vibrate, and it has the double benefit that:
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Of course, that's the obvious comment (no offense). But consider: What if you're wrong? Imagine being in Times Square a few years from now, watching the crowd look around like lemmings... *chussh chussh* everyone looks at the Pepsi add *chussh chussh* everyone looks at the CBS add *chussh chussh* everyone looks at the ticker *chussh chussh* everyone looks at the Pepsi add. Repeat as desired.
A scene that fits right into the Matrix.
Anyhow, the humorous image merely underscores my point: While it's virtually doomed to failure in the way you describe, it would be even worse if it actually worked. This thing is violation of Jerf's Law: Never try to do something where the worst case scenario is success.
A new sound ... that is less intrusive yet easy to pinpoint
Cellphones that fart. That's just great.
--
Mod up a post Rob doesn't like and you'll never mod again
Coming from a country where headlights are compulsory at all times, I have noticed that cars without headlights (I'd say less than 1% of the cars during daytime) are a lot easier to miss; possibly because the brain subconsciously writes them off as being parked. It's really kind of spooky the way you just don't notice them until they are really close.
So, I'd say the risk with this kind of sound might well be that people will disregard the old kind of alarms even more when we've all gotten used to this new sound.
You have to put up with a three minute interview and a horrible site design, but it's here, in RealAudio and Windows Media, along with a demonstration in a smoky room. The sound is more like a compressed air can, and I would swear it's being produced by an air compressor.
When they say "impossible to ignore", they're not saying your head instantly turns to it - they're saying that in a smoky room, you can pretty well tell where it's coming from without having to think or concentrate on it. Believe me, my head didn't instantly gravitate toward my laptop speakers when the sound came on.
What's your damage, Heather?
Some spelunking through the mess of javascript turned up this:. akamai.com/2611/2001/06/18/0000522955.rm
http://mfile.akamai.com/2611/rm/twimedia.download
It plays at ~100kbit for me.
All those curves and curls in your ears focus different frequencies differently according to where the noise is located. That's part of what you spend your childhood doing. When there's a noise, your eyes search for it, and your brain remembers, "that's what a sound, from that direction, sounds like." In order to determine direction, the sound needs to have frequencies that your ear can attenuate so that you can determine direction.
That's part of why music through headphones doesn't sound like it's coming from somewhere (nothing reflects off your ears). Throw in tone purity (purer tones being directionless), and you'll see the problem. Some songbirds you really have to look for when they sing. Crows, on the other hand, with their non-pure calls, you know where they are right away.
Correct. `Vibrate then ring' is a wonderful thing: heck, it's even pretty good if the two happen simultaneously (as with my replacement for the Motorola, the Siemens SL45).
.|` Clouds cross the black moonlight,
However, I'm worried about misuse of this noise. If I'm on an oil-rig and hear some static kind of noise like this, turn to look at the mobile, think "oh, wasn't the mobile, must be an emergency then" then I've lost a few precious seconds.
IOW, don't use it for *everything*. Work on expanding your braincell to cope with different noises for different things. (How many folks here have per-caller ringtones, but never actually *use* them preferring the visual instead??)
~Tim
--
~Tim
--
Rushing on down to the circle of the turn
Not only the sort of cry it's using. When I was a baby for some reason or another I developed a strong liking for droning--that is, humming a single note for a prolonged period. She could tell where I was and what I was doing my the tone of the note. If the tone changed to `curious,' she knew she might need to go make sure that I wasn't getting into something I shouldn't (like Draino); if it stopped altogether, she knew I was either in trouble or asleep. Fortunately, for a baby `trouble' as often as not means `having to use brain,' as in figuring out how to climb stairs.
Incidentally, as I wrote this I was droning to a rockabilly tune and than Also Sprach Zarathustra. You see, it's a habit I've yet to break...
The way the site demos (but doesn't SAY) you get around this problem is by combining sounds. For instance, let's say you have a standard "alarm Hooter" - You play the hooter to let everyone know the KIND of alarm, and the directional tone to let people know WHERE to look
"Hoot chsssh, Hoot Chsssh"
If you look at the streaming video, the had a standard fire alarm going off, with the EXIT marked with the "chsssh" You follow the "chsssh"
-- 73 de KG2V For the Children - RKBA! "You are what you do when it counts" - the Masso
http://www.soundalert.co.uk/research.htm
I still can't find actual audio files, though.
--
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Someone provide a link to the sound. Please.
(from a user sick of his current AOL IM sounds)
I hope not!!! I just listened to all the MP3s - and these things sound similar to the bugs (not sure if they are cicada's or not) we have here during the monsoons in Arizona.
Just yesterday we had a pretty humid day, and they came out in full force - I am up in an office on the fourth floor - and they were still loud!
If this is the sound it makes - aggggh!!!
Worldcom - Generation Duh!
Reason is the Path to God - Anon
...so does this mean nobody will now be able to distinguish "ssssshhh! sssshhh!" among the din of "chussshh! chussshh!"...I can't wait for ringers that sound like "shudupgodamu! shudupgodamu!"....
It's 10 PM. Do you know if you're un-American?
Years ago, I read about some research that was seeking the sound most likely to wake a person up with the least actual volume. What they came up with was a recording of a crying infant, which apparently we're pretty much hard-wired to react to.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
I read about this yesterday on the BBC. A much better article.
Because hearers of the new noise are virtually unable to resist turning to face the direction from which it is coming, banks and shops are evaluating its potential for catching criminals.
There was a time when a car alarm going off caused everyone to turn and look, but now they're so commonplace that nobody turns to look at a car when the alarm is going off. If this new noise is going to be used in phones and alarms everywhere, it shouldn't be long before people become desensitized to it as well.
I would have to also wonder about getting so used to the sound that it loses its meaning.
Some time ago, I figured that I didn't need to use bookmarks since I could just commit the page number to memory. And it worked fine (I'm not particularly amnesic...) But after a while, I found it harder and harder to return to my place. Not because I could not remember the page number, but because I remembered ALL OF THEM, and didn't know which was the correct one. In other words, I had exhausted the usefullness of this memory exercise.
I also have to question the conclusion of those "researchers" that decided that your car was safer with the headlights always on. I believe that they based their conclusion on some studies that suggested a connection between cars with headlights on and lower accident rates. AN APPARENT CONNECTION PROVES NOTHING! I have to wonder if the lower accident rate was due to the fact that it was unusual for cars to have their headlights on (during the day), and that other drivers were just paying more attention to THOSE cars...
For all we know, if all cars had their headlights on, the accident rate might return to the same place it was beforehand.
Anyway, I agree with you that certain stimuli may lose their advantage when they are commonly encountered.
A dingo ate my sig...
I've lived in New York for 4 months now and I still can't tune out the trucks with oil-tanker fog horns installed. I'm a pacifist, but I just want to choke them when they honk at 4 AM outside my bedroom window! arrghgh
Frogive me, but I can't imagine gridlock in New York with everyone chusssh-chussshing each other.
LS
There is a fine line between being a cultivated citizen and being someone else's crop. - A. J. Patrick Liszkie
This is a perfect example of a mostly hype-driven story. Basically, the headline should really be this: "Directional acoustics applied to alarms". Unless the article is missing something, there is really nothing new here. Directional acoustics have been around for a while, and are used by your sound card drivers for "3D" sound. The video at the article link looks like your typical "Beyond 2000" fluff piece.
Come on Slashdot, isn't there a more interesting technology out there being developed? Like bionics or new genetic engineering or some new materials science???
LS
There is a fine line between being a cultivated citizen and being someone else's crop. - A. J. Patrick Liszkie
I hate to nitpick, but this is important. They say a wide spectrum of frequencies, which does not necessarily denote white noise. The article never mentions white noise.
Every signal can be broken into frequency components, and each component has an amplitude *and* phase (often this is expressed by adding negative and positive frequency components). The importance of these phases cannot be overemphasized. If you "coherently" add components with the same phase, you will get a delta function: a single large crack. If you add them with random phases, you end up with white noise.
It is quite possible that the sound they are talking about is more like a series of short, broadband "chirps" than white noise.
I don't know enough of the physiology of hearing to know what makes things easy or difficult to locate, but I expect the incoherent nature of white noise makes localization more diffcult, not less. A chirp on the other hand, has a very steep rise that makes time-of-arrival measurements relatively easy, and improves localizability.
What, psychologically compells one to look at the source I don't know, but I have serious doubts that it will be effective in the long term. Human brains have a remarkable ability to get used to things and start ignoring them. Only while this sound is new and rare will it excite such reactions.
The claim that it forces humans to turn and look is probably a little outlandish. You'll become accustomed to the sound if it becomes ubiquitous in advertising.
/is/ interesting, however, that the sound is far mor easily locatable than previous alarm sounds.
It
Incidentally, every time I hear a siren, I tend to turn and look (even if the sound isn't as easily locatable). But I dont hear that siren sound in advertising all the time. So I'm not as fearful as others here in terms of advertisers monopolizing this sound, as the claim that you HAVE to turn towards it is probably exaggurated a little. In conjunction with noise pollution laws, I doubt you'll see a proliferation of this sound in advertising. I'd imagine emergency alarms and cellphones might make a little more use of it.
"Old man yells at systemd"
Integrating this sound into cell phones may not have as great an effect as forseen. First of all, a cell phone "feature" is being able to choose your ringer song, and on some models, write your own. Also, most cell phones have this feature called "Vibrate." Such a feature makes your phone "vibrate" letting you "feel" that it is YOUR phone that is ringing, not someone else's. Also, with vibrate on, and your "ringer" off, no one is compelled to turn and look at your crotch. On a different, note, who's to say that this urge to turn and look for the source of the "new" noise won't fade as we are immersed by it. People no longer react the same way as they used to to sirens. We don't even react as harshly to crime and death since we see it everyday. What happens when our attention is no longer captured by this sound... find another?... and another?... and another?...
"The best laid plans of mice and men gang oft agley..." - ROBERT BURNS
Only sounds I could think of that might be marketed like this are regular fire alarms or copyrighted/trademarked theme songs, which wouldn't be marketed if the sound is meant to illicit brand recognition.
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Linux: The world's best text-adventure game.
Gawd, can't wait until I can't resist turning to the prick sitting two seats down in a final exam who can't turn the ringer off.
On the plus side, I now know how to get my /. postings read by everyone: include "chusssh chusssh chusssh" in each message, then all /.ers will be irresistably drawn to my post!
---
Linux: The world's best text-adventure game.
This is not the first time that sound has appeared. You see, horror movie directors have hit upon it time and again.. trying to reproduce the sound that signals a fight or flight response like when you hear something (a bear, a murderer, a grue, whatever) sneaking up behind you.
Maybe ten years ago or so we used to play with making the sound from one horror movie, which sounds like "Ch-ch-ch-ch-ch Ah-ah-ah-ah-ah", as if you just said the Ch and the Ah into a circuit which generates reverberating echoes.
It also sounds a lot like the sound of the daleks in Doctor Who which scared the shit out of me.. guess I'm susceptible to that kind of sound.
But listening to the audio, it seems that they are going way overboard on their application of the sound. I think it is going to give some people heart attacks and make genuinely frantic, not simply provide directional cues but actually get people into a nervous, crowd stampede state of mind, as if one was running through a nightmare.
Also, you usually run *away* from such sounds, not towards them. It is going to be a lot more effective if they can just add a small crackling component to ordinary rings and buzzes if necessary and forgoe a full sonic rendition of your worst childhood nightmare.
Finally, user selection of ring tones, to the point of symphonic midi rendition of popular songs, is already big business in Japan. You can even compose your own with a system my friend made called theta, at mobile.yamaha.com. Only unimaginative people will find themselves picking up their phone at the wrong time, most people have something interesting and people around them laugh and appreciate neat, beautiful music instead of irritating rings. That "whose phone is it" thing may be true but it is also a canard, based on low tech in the U.S. and Europe in this regard.
I think people are going to have to be very careful implementing this because it can be dangerous, in the same way that Japan Rail now has to tell people over and over again to not use their phones on the train because they interfere with pacemakers. You might get more hypertension and people with nervous conditions if such nerve- wracking sounds become prevalent. Once you open Pandora's box.. it could be like being submerged in an Indiana Jones style nightmare of endless slithering insectoid things.
Sorry that's http://mobile.yamaha.co.jp/ which links to http://myc.thetamusic.com/framesets/myc.html. It's a Java sheetmusic composer for 16 voice midi; most of the phones now have sophisticated midi engines and instrument libraries in them now.
It sounds like a TV with just static. Scientists have known since the early 80s that people are inescapably drawn to the sound of a staticy TV.
120 characters isn't enough to explain it.
They say a mother can tell exactly what a baby wants by it's whine. Maybe this would be a good basis for a phone ring sound. With just a peep a well trained ear can tell that marketing hit development over the head with the lego bucket again.
Who moderates the meta-moderators?
"Because hearers of the new noise are virtually unable to resist turning to face the direction from which it is coming, banks and shops are evaluating its potential for catching criminals."
Oh c'mon, if this works as well as he says, you know the main application will be advertising. Beer cans will be chusshh-chuusshh-chusshing from the aisles before a bank robber is ever caught looking at a chussh-chuush-chuushing security camera.
Anyway, just wanted to say that it seems like another wheel reinvented.
If programs would be read like poetry, most programmers would be Vogons.
"Because hearers of the new noise are virtually unable to resist turning to face the direction from which it is coming..."
and"The new sound could also rid everyday life of one of its embarrassing moments, when everyone in a room searches for their mobile phone when just one rings.
That's right, now instead of everyone ruffling through their clothes checking their phone they will ALL look at YOU. No, not embarrasing at all...The new sound could also rid everyday life of one of its embarrassing moments, when everyone in a room searches for their mobile phone when just one rings.
And at a new embarrassing moment, when the entire room is unable to resist turning to face your crotch.
ok then your [sic] infringing on my copyright! Could you as [sic] me next time before STEALING my comments for your own?
Consider yourself blessed if you are sneezed on by a dragon and only get wet, it could have been a fireball.
There is a link to an interview with a video clip lower on the page.
Nice clip, educational.
Chussssh chussssh chussssh is not really the sound. It is just pulses of white noise. Definitely less harsh than a simple buzzer. Niceties include varying the pulse speed depending on how close you are to the exit, etc.
Pulses of white noise have a better chance of being directional and cutting through the other background noise in an emergency.
They are really just navigational aids for humans. I do not think sirens are going to go any place for a while
"It is a greater offense to steal men's labor, than their clothes"
If it is actually put in all these different devices... how long do you think it'll be before we automatically tune this one out, too? Living in New York City, we learn to tune out a lot of annoying noises... like the ubiquitous multi-tone car alarms.
Portable versions of Firefox, GIMP, LibreOffice, etc
Have you ever deer hunted or do you go on walks in the country? Often a sharp quick whistle is all it takes to stop varmin dead in their tracks.
Although this doesn't always work for deer, it has occasionally worked for deer. It almost always stops rabbits, squirrels, and birds.
What you do is let out a sharp whistle as soon as the said varment is spooked, as it is running away. You'd be amazed how often the creature stops in its tracks and turns to look at you. Of course it might start running again after it notices you, but try it.
The article makes it sound like the chussh-chussh-chussh does something similar to humans. I think this might endanger more lives than it would save.
Keeping
Now what are people going to do to tell people their phone is being noisy?
Donate background CPU time to fight cancer.
Ok, look. I ran white noise through a sonogram. Then pink noise. Look at them and then tell me if I am wrong.
--- At my sig, unleash hell.
Something tells me this sound is going to, well, sound like "Pink Noise." Pink noise is spectrally-ballanced; it contains all the frequencies from about 20Hz to 20KHz (or whatever range the audio engineer chooses). Pink noise is very "ear catching" due to the fact that the sound is so broad-band. They probably just applied an envelope to the sound and said they came up with something new. We'll just have to see.
--- At my sig, unleash hell.
Now as opposed to them just disturbing your listening to the movie, you'll be forced to look away from the screen too.
Anyways, here's an explanation of how their new sound works.
According to The CSound Book (http://mitpress.mit.edu/e-books/csound/fpage/pub/ csbook/csbook.html), pink noise is noise in which the power density decreases 3 dB per octave with increasing frequency (density proportional to 1/f) over a finite frequency range. Each octave contains the same amount of power.
http://www.premierhazard.co.uk/sirent.html(Java version) http://www.premierhazard.co.uk/sirentnj.html> (non-Java version) The sounds are from Premier Hazard, a licensee of the sound.
I'm a bit confused about this.
My phone rings chussssh chussssh chussssh
Someone's car backs up chussssh chussssh chussssh
A fire engine goes past chussssh chussssh chussssh
An elevator is available chussssh chussssh chussssh
Some idiot with a chussssh chussssh chussssh-sound maker goes chussssh chussssh chussssh
How long before I become acclimatized to chussssh chussssh chussssh?
The article says that the sound "initiates a reaction that makes you instantly turn towards [it]". If this is true (which I doubt) and the sound forces its way out of your cell phone while in heavy highway traffic, what happens to you and your vehicle when you turn your head from the road to the phone?
"Anyone hearing the broad-band sound should immediately know the precise location of its source"
Yeah, the URL is right over here.
No, wait, here.
Oh, hell...I don't know.
Hmmm...I guess it doesn't work so well at providing its location as they think :-)
It's at uspto.gov; yes, they do talk about white noise, among other "embodiments". The claims are pretty broad. Of course, sounds like these have been used before in alarm clocks, signals, and horns; giving a scientific explanation for its utility doesn't warrant a new patent.
It increases your sex appeal! Yes, all you Slashdotters can now have women feel irresistably drawn to your presence! Just set your pager to "chush", give yourself a page when your signifigant-other-to-be is around, and watch what happens ;)
Since apparently "it is impossible for people who hear the sound not to turn and face" this sound; if two or more of these phones go off simultaneously, your head will just tear clean off.
I wonder if this is our innate reaction to the hissing sound of a snake ?
I'm sorry if this has been posted before, but i'm tired and there is a *lot* of nested posts on this topic, too many to read through at work :)
Anyway, a UK TV programme showed footage of this "new sound" in action. They stuck a speaker on a security camera and got people to walk past it without knowing the location of the CCTV or anything about the test. Every time a PIR detected a person walking by it played the sound and everyone instinctively looked in the general direction of the camera, catching a good image of their face. They then tested people who were aware of the system and told them not to look up no matter what - and still the same knee-jerk response to the sound.
They then got some people to watch a horror/action film and do the same walk to try to emulate the sense of apprehension that store thieves may be feeling while stealing. Response to the sound was even greater and a better image was captured.
Finally they put the same set-up "in situ" in a shop and got a policeman who specialised in catching shoplifters and the techniques they use to avoid being caught. He had no idea about the speaker, and successfully avoided getting a good face image from any conventional cameras, but *still* got caught out by the new camera.
It all comes down primitive parts of the human brain interpreting the sound as a threat, making them turn to face the danger. This is similar to being in a wood at night and hearing a twig snap.
Oh, and a lot of ambulances around where I live use the broadband sound to allow you to pinpoint where they are - it really works
The sound is just an up to date application of the sharp hissing sound used almost universally by people to attract attention. Here in the UK it is not unknown (though considered pretty rude) to make a "psst" noise with the lips, tongue and teeth to make someone look your way (think secret agents in dark doorways!). I spent 3 years installing science equipment and PCs in Ghana and found that the commonest way to get peoples attention (and considered perfectly acceptable) was to make a similar "tss" noise, then beckon to the person you want when everyone looks your way. All these sounds share the broadband hiss that through a variety of mechanisms, presumably to do with the shape and dimensions of the outer ear, and the fact that some frequencies are attenuated more by passing through the head than others, are highly directional. It can't just be attenuation through the head though, since (as the Tomorrow's World episode referred to elsewhere) it is also directional in the vertical direction - i.e. if the sound is coming from above you, you'll look up.
"E pur si muove!" - attributed to Galileo Galilei, 1564-1642