Rocket scientist converts stereo into 3D sound

Princeton University professor Edgar Choueiri not only designs plasma rocket engines, he invented 3D stereo!

Steve Guttenberg
Ex-movie theater projectionist Steve Guttenberg has also worked as a high-end audio salesman, and as a record producer. Steve currently reviews audio products for CNET and works as a freelance writer for Stereophile.
Steve Guttenberg
3 min read
The sound lab at Princeton University; note the close spacing of the stereo speakers. Steve Guttenberg

Edgar Choueiri is a professor of applied physics at Princeton University, where he is the director of the Engineering Physics Program and the chief scientist of the university's laboratory for advanced spacecraft propulsion (the Electric Propulsion and Plasma Dynamics Lab). Right, he's a rocket scientist, but he's also an audiophile.

Professor Choueiri's Pure Stereo system is a "Revolutionary Technology for Audiophile-Grade 3D Audio." I was treated to a demonstration in Professor Choueiri's lab in Princeton, so I can tell you it really works. The professor played a variety of commercial classical and rock recordings, including Led Zeppelin, over a pair of closely spaced speakers (see photo). The sound spread to the full width of the room, and projected sound forward. He also played recordings he made, including a "haircut" with the sound of "scissors" snipping away all around my head. Professor Choueiri's 3D claim is no hype; Pure Stereo sounds amazing.

The technology can be used with any stereo system, and can operate in any resolution, including high, 192-kHz sampling rates, at 32-bit resolution. Pure Stereo is also compatible with analog sources like turntables and FM radios. Professor Choueiri doesn't equate Pure Stereo (two speakers only) with surround-sound systems that produce envelopment from multichannel music or movie soundtracks from five or more speakers. Pure Stereo's goal is to create more accurate spatial reproduction from two-channel recordings.

It's Professor Choueiri's assertion that stereo playback over loudspeakers is a deeply flawed concept because "Crosstalk corrupts the natural transmission to the brain of 3D cues that exist in all stereo recordings." That is, crosstalk occurs in normal stereo listening when your ears hear both the left and right channels. Professor Choueiri's Pure Stereo BACCH (Band-Assembled Crosstalk Cancellation Hierarchy) filter algorithm prevents your left ear from hearing the right channel speaker's sound, and your right ear from hearing the left channel speaker's sound. Professor Choueiri is hardly the first to develop such a crosstalk filter, but he may be the first to make one that doesn't adversely affect sound quality in the process. The Pure Stereo 3D filter is said to "purify" (eliminate crosstalk) between the two speakers and allow the listener to more accurately hear spatial cues in stereo recordings. In addition, the Pure Stereo 3D filter can provide room correction, to reduce acoustic problems in real world spaces.

Edgar Choueiri at work Steve Guttenberg

Once the crosstalk is eliminated stereo recordings take on a 3D quality; the soundstage is wider, deeper and significantly more solid and realistic sounding. Professor Choueiri has developed three types of BACCH filters: the u-BACCH, a universal filter that can be used with any hi-fi system, without any adjustments; a t-BACCH (theoretical) filter that only requires the end user to input the distances between the two stereo speakers and the listening position in the room; and a c-BACCH filter custom-designed using the audiophile's own head to work with the user's ears, hi-fi system and listening room. The c-BACCH filter provides more exacting spatial cues than the other filters, but I only heard the u-BACCH, and it sounded great to me.

As it stands right now you can't buy a BACCH filter directly, but Professor Choueiri told me that Princeton University has just licensed a local custom installer company (Audtech Associates) to design Pure Stereo c-BACCH filters for audiophiles. Audtech Associates will integrate the filters in their customers' stereo systems. All of this is just now starting to take shape, and the Professor also told me Pure Stereo will also be used in some form with 3D video displays in the near future.

Professor Choueiri's Web site is the best place to find the latest information about Pure Stereo. While you're there, take a few minutes and watch Mike Wood's video, "Introduction to 3D Audio with Professor Choueiri" that demonstrates how Pure Stereo works.