Tag Archives: 3D sound


Last Autumn I received an email out of the blue from a Professor Edgar Choueiri who introduced himself thus:

Dear Mr. Weiss,

I am the director of  the 3-D Audio and Applied Acoustics (3D3A) Lab at Princeton University, where my research group has been focusing on binaural audio reproduction through two loudspeakers using optimized crosstalk cancellation filters.

Over the past few years, I have developed a method for deriving crosstalk cancellation filters (called BACCH filters) that are optimized to minimize spectral coloration while maximizing crosstalk cancellation between two speakers and the contra-lateral ears of the listener.  The resulting audio is of unprecedented spatial reproduction realism from a two-loudspeaker system (it is able, for instance, to reproduce the sound of a buzzing fly around the head of a listener, or the detailed 3D staging of a musical ensemble  with high spatial accuracy).  This is not an attempt at a standard surround sound but the goal is rather a highly accurate spatial reproduction of 3-D sound fields.  The technology, called BACCH 3D Sound, has been patented by Princeton University and is being licensed in the audiophile, pro and consumer audio markers.

He went on to say that he’d like to demonstrate BACCH for me, either at our showroom  in NYC or at his lab at Princeton, and he was interested in our horn loudspeakers too.

I was rather surprised to get this email. I’d read about Choueiri and BACCH in the New York Times a few years prior. It seemed interesting in a theoretical sort of way. But nothing that I thought would have anything to do with my area of hifi.

How wrong I was.

Now I was curious about Choueiri. This is just the list I found of his positions at Princeton University:

Professor of applied physics at the Mechanical and Aerospace Engineering Department ofPrinceton University, and Associated Faculty at the Department of Astrophysical Sciences,Program in Plasma Physics. Director of Princeton University’s Engineering Physics Program. Chief Scientist at the university’s Electric Propulsion and Plasma Dynamics Lab, a recognized center of excellence in research in the field of advanced spacecraft propulsion.”

Basically, Choueiri’s day job is designing plasma rocket ship engines for space travel. He also has been a very serious audiophile for decades, with an enormous collection of priceless master tapes (the reel to reel tapes from which records are made) and has done his own recordings as well. Princeton had given him carte blanche to pursue a solution to the holy grail of hifi- 3D sound from a pair of stereo speakers. Private corporations like Sony were also involved, and Choueri’s sound lab at Princeton was almost as big as the one with the rocket engines.

Choueiri was not the first to try to create 3D sound- there have been many attempts and all failed. I attended a demo of a technology called Ambiophonics years ago, and the results were miserable, worse than not trying in the first place.

3D sound is really very similar to 3D visually. You have two eyes, as you have two ears, and the reason a movie, for example, is visually flat is something called crosstalk. An easy way to understand crosstalk is to look at the first gadget that allowed you to experience a 3D image- the stereoscopic viewer. You wore this device on your head, and looked at two images of, say, the Leaning Tower of Pisa, each taken slightly offset. To keep your left eye from seeing the right image,and vice versa, there was a little piece of cardboard that was stuck in the middle of your forehead. With the visual crosstalk thus eliminated, your brain miraculously processes the two images as a single, 3D image!  The colored glasses you wear in a 3D movie theater do the same thing. If you remove the glasses, the result is blurred and discomforting.

As Choueiri later explained to me, listening to stereo sound is like watching a 3D movie without the glasses. Stereo sound is not a natural thing. The sound from the right speaker should only go to your right ear, same for the left. But that is not what happens, and the resulting crosstalk is confusing for your brain. You generate (best case scenario) a phantom image between the two speakers in stereophony, but if you could get rid of the crosstalk, you would have 3D sound, and you would also enjoy music more because your brain could relax and not have to process the crosstalk.

To do this, two things are required. An incredible mathematical and engineering feat, and the hardware and processing power to enact it. Choueiri, with Princeton’s backing, had seemingly mastered both.

Within a very short time from receiving that first email, Choueiri arrived at my doorstep with the proverbial black box, about the size of a powerful amplifier. The box connects to your system, between the source (like my turntables or CD player) and the amplifier. Choueiri had me sit in my usual spot, and gave me what looked like a stethoscope with two tiny, laboratory grade Danish microphones which went inside my ears. The BACCH system uses an iPad, which Choueiri has programmed for the user so intuitively and simply that it could have been done by Apple. With a couple of touches on the iPad the black box sent a test signal through my system, out of the speakers, and measured what each of my ears was hearing. This took less than a minute. The stethoscope thing was retired, and the box now had an extremely accurate measurement of my “head transfer function” or the way my head, torso and pinnae (the outer ears, which are unique to each person) effect how you hear.

The way you can uncannily identify the direction of a sound source, like where you dropped your keys, is by the tiny difference in time and level that it takes for a sound to reach each ear. Your brain makes unbelievably fast and precise calculations that tell you where a sound is coming from by judging the differences in time and level of a source as it reaches each ear. The way BACCH works is by correcting the sound reaching each ear from your stereo speakers, in real time, and even if you are moving about the room (via a camera which tracks your head’s movements.) How this works is beyond my meager technical abilities to explain, but for the math inclined an elucidative white paper can be found on the BACCH website.

Sitting in my own showroom, surrounded by equipment which I know intimately, because we make it, I did not know what to expect. What happened next, however, is certainly one of the great surprises of my audio life.

With world class speakers and attendant electronics, you cannot tell that the sound is coming from the speakers, it just appears in front of you, but between the speakers (and always, between the speakers.) It does not surround you, it can’t do that. It does not approach you or envelop you either, it can’t do that. As good as it can be, you are always aware that you are listening to music reproduced through a stereo system (at least I am.) When Choueiri ran music through the BACCH box, all that changed. Suddenly music was everywhere, and it was definitely three dimensional The better it was recorded in terms of spatial cues, the better the 3D effect. If a fly was recorded using a binaural head, the most sophisticated way to generate accurate spatiality, then the fly was buzzing around your head. As Arthur Clarke once noted, “any sufficiently advanced technology is indistinguishable from magic.” What I was now experiencing was audio magic, but it really felt like someone had slipped me some LSD, to be honest. Hallucinatory.

Even if a recording did not have any spatial cues, because it was created, for example, by multi-tracking in a studio, where there is no space surrounding the performers, I noticed something else happening with BACCH that was also amazing. The music felt much more enjoyable to listen to. It was like taking off a pair of too tight shoes, you don’t know how unpleasant they were until they’re off. Without the crosstalk, all music was much more enjoyable, a very unexpected result.

Choueiri left that evening as swiftly as he had come. He’s an elegant man, in an old school European way (he is Lebanese) always impeccably dressed, someone for whom aesthetics matter greatly. He had explained to me one problem he had- for BACCH to work well, you need a loudspeaker that has very good directivity. That way the crosstalk cancellation will be effective. You can get BACCH to work perfectly with any speaker (even a really bad, cheap speaker) in an anechoic chamber like he has at Princeton- there are no reflections of sound in an anechoic chamber. But we don’t live in anechoic chambers. Choueiri has a pied a terre around the corner from the Metropolitan Museum of Art in Manhattan, furnished with beautiful Scandinavian and Czech art deco furniture, pre Hellenic vases and ancient art. The space was basically a sonic nightmare, with virtually no absorption and little diffraction, a very reflective and reverberant room. He knew this, and he was not about to change the room one iota to make it more audio friendly. Choueiri asked if I would bring the OMA Mini loudspeakers over for a test. He needed speakers which mitigated the problematic room acoustics and let BACCH do its thing. They never left his apartment.

Eight months later, the first BACCH SP units are in production, and are slated for release this Summer. OMA will be the first North American dealer/distributor and representative for BACCH. I hope to have a unit available for demo at our Brooklyn showroom from August of this year. I’ll be posting more about this soon, but suffice to say, it’s a great vote of confidence by Choueiri to choose OMA to release what I fully believe is the most important qualitative innovation in audio in more than half a century.

We’re already working on the new BACCH SP section of the OMA website. Stay tuned…