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Sound – It’s rocket science

With 3D images astounding half the population and leaving the other half feeling distinctly seasick, it was only a matter of time before another of our senses got the same treatment.

18 June 2011

12:00 AM

18 June 2011

12:00 AM

With 3D images astounding half the population and leaving the other half feeling distinctly seasick, it was only a matter of time before another of our senses got the same treatment. Sure enough, 3D sound reproduction is finally with us; but while you might expect Professor Edgar Choueiri, its inventor, to be an audio engineer of some sort, he in fact spends most of his time as professor of mechanical and aerospace engineering at Princeton University. Let the ‘3D sound? It’s not rocket science’ gags commence.

Born in Lebanon and schooled in France, Choueiri now works on spacecraft propulsion in the US, funded by Nasa. But in 2003 a lifelong passion for music led him to wander into a conference of the Audio Engineering Society, where he heard people discussing 3D audio, and why no one had managed to perfect it yet. To Choueiri, this sounded like a challenge.

So he went and did what any good professor would do — read ‘what I think is every paper on the problem’. He soon learnt that any stereo recording (that is, any recording made through separate microphones) — which is almost every recording from the past 60 years — contains enough information to be reproduced in 3D, but, because of sound’s frustrating tendency to spread out from loudspeakers, some of the sound meant for the left ear is picked up by the right ear, and vice versa, destroying the 3D effect. ‘Stereo kind of fell short,’ explains the professor. ‘Imagine watching a 3D movie — if you take off your glasses, the image won’t be in 3D. That’s what happens when you take a good recording and play it through your home stereo — you are seeing without the glasses.’

The way to fix this is using a technique called ‘crosstalk cancellation’, which I asked him to explain in terms it wouldn’t take a PhD to understand. ‘Take a mattress,’ he said, ‘and place it vertically between two stereo speakers. If you sit with your nose touching the mattress, you’ll hear in 3D, because the sound from each speaker is only reaching the ear it’s meant to reach.’ This is a rudimentary, if somewhat uncomfortable, example of crosstalk cancellation; and people have been trying to recreate the mattress, in digital form, for years. But they always encounter the same problem: any 3D digital crosstalk cancellation filter changes the sound so much that it is unacceptable by most audio standards. Choueiri, however, applying tools from his plasma physics background, has designed a filter that is ‘transparent’, meaning the sound isn’t affected at all; and he has found what he calls the ‘optimal solution’, which in any other field might sound like arrogance, but in something like plasma physics actually means what it claims.

If this strikes you as little more than surround sound, don’t mention it to Professor Choueiri; it would be like telling Edison you already had a perfectly good candle. With surround sound, sounds may come from specific directions, but they will always be clearly emanating from the speakers; with 3D audio, however, a fly can be made to sound like it’s circling your head. Quite apart from the obvious applications in the film industry, this technology will be available for hearing aids, security and teleconferencing — so why isn’t it already out there? Why isn’t it being fawned over by Steve Jobs and his ilk, available first in black and then, after months of painstaking research and development, white?

Well, the first licence has been signed — Choueiri can’t disclose with whom, but you can bet it’s someone big — and within a couple of months you’ll be able to buy small, wireless speakers specially designed for 3D listening. Then there’s interest from Hollywood — after talking to me, Choueiri had to rush off to have lunch with someone who wants to make the first short film combining 3D image and sound. And, on top of all this, he and his team have been working with British firm Cambridge Mechatronics on a device that detects all the listeners in a room and directs sound beams to their ears, so that each person can hear in 3D. Before this development, the 3D experience would have had you rooted to the spot — now, however, it looks as if you’ll be able to roam around your own virtual concert hall.

Having made arguably the biggest leap in sound reproduction technology since the Allies stumbled across magnetic tape when they captured Radio Luxembourg in 1944, the pressure is now somewhat off Professor Choueiri, and he is taking whatever time off a rocket scientist gets to rediscover his entire record collection in 3D. But he shouldn’t relax just yet: Nasa is going to have some serious questions about how he’s been spending his time.

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