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Musical sweet spot for 3D sound

By Matt Wells
Today programme

Sound wave and ear

An enhanced way of creating 3D sound using computer software is attracting interest from the TV industry and Hollywood.

I am standing in a foam-clad chamber with my eyes closed, listening to the sound of scissors dancing around my head.

All that is missing from a real visit to the barber is the feel of hair dropping to the floor.

This virtual reality "3D" audio experience is the product of Professor Edgar Choueiri's life-long passion for recorded music.

The Princeton University physics professor's main day job is working on space rocket propellants.

But striving to make his own listening experience as real as possible led him to start designing an audio filter for standard stereo speakers, which goes a step further than conventional surround-sound.

Professor Edgar Choueiri
Prof Choueiri is the only person able to design his 3D sound filters

"Surround-sound can give you a sense of an explosion happening at a distance, but it's not accurate," says Professor Choueiri, sitting in his custom-built acoustics lab on campus.

"With 3D audio, I can get a fly to go around your head… or if you want to really scare somebody, you can put a sound inside their head."

His breakthrough is a small one, he is careful to say.

The brain-tricking effect can be created in other ways, and other pioneers have achieved it.

But none of the solutions appear to be as simple - or it seems, commercially viable - as his software filter, based on mathematical algorithms.


By eliminating what is known as "cross-talk" from ordinary stereo systems - when the left and right ears hear sounds that they do not in real life - his unique filter relies on the listener being in a small "sweet spot" between two speakers.

"Right now, I'm the only one who can design the filters, until we train somebody," he adds.

Princeton sound lab
3D sound has taken far longer to crack than 3D vision

The 3D effect is most pronounced inside the anechoic (echo-less) chamber at Princeton Sound Lab, but the professor shows it can also work on a small wireless speaker linked to a simple laptop.

"3D vision goes back to 1895, people cracked it then. 3D audio turned out to be a much more difficult problem," he says, with just a whiff of the mad-professor, bubbling over with excitement at a new discovery.

Princeton University has patented his technique, and recently teamed up with the British-based technology company, Cambridge Mechatronics, to design a 3D sound system for 3D televisions.

They say they have already managed to crack the problem of creating multiple sweet-spots in a single room for family viewing.

Hollywood production studios are taking an interest in this pipe-smoking academic's work - helped, he says, by his unlikely friendship with the US's leading magician, David Blaine.

Wired for 3D

On the day we met, Lebanese-born Professor Choueriri had just returned from demonstrating his filters in Los Angeles to, among others, the producer of the movie Avatar, and the co-president of Columbia records.

It is clear that the attention his breakthrough has received from the entertainment world is a thrill.

But he also points out it could help to advance hearing-aid technology, and that in scientific terms, having optimised the filter design, his contribution is over.

The professor is already enjoying the benefits of his own invention. His home's music system is wired for 3D.

Equipment used for sound testing
Not all those in the Princeton sound lab enjoy the experience

We take a musical tour from Bach to Led Zeppelin, and sitting in the sweet-spot, I felt as it is as if the performers are there in the room.

He is also an avid collector of rare original recordings and even has a copy of the first ever stereo release from 1954. The 3D enhancement can be used to listen to the vast majority of existing stereo music, he explains.

Unlike its visual counterpart, there will be no need to re-do your favourite discs for 3-D listening pleasure.

So is this really the dawn of the virtual world, I wondered?

"Imagine not only hearing a fly going around your head, but you'll be seeing the fly going around," says the professor.

"And the next thing is for when the fly lands on your nose, somehow, there will be sensors that excite your nose, so you can feel it."

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