I’m standing in the confined space of a custom-built anechoic chamber at Princeton University’s 3-D Audio and Applied Acoustics Lab, bathed in green light and surrounded on all sides by wedges of melamine acoustic foam. I’m facing a pair of Ascend Acoustics speakers set on tall stands about a foot and a half apart. And I’m considering the advice that professor Edgar Choueiri has just offered, in a voice curiously deadened by a total absence of room reflections.
“You may want to close your eyes,” he said. “If you clear out the visual cues, you get even more realism.”
I’m about to hear a demonstration of Choueiri’s Pure Stereo filter, which promises “truly 3-D reproduction of a recorded soundfield.” Only a handful of people have heard his 3-D demo, but it’s already spawned awestruck hype, as well as preemptive rumblings of audiophile skepticism.
Choueiri leaves. A few seconds later, the sound of flowing water fades in and rises in both volume and presence. I have the uncanny sensation of standing neck-deep in a river, with its plashing surface spreading around me. Next, a buzzing fly circles my head. Then an aural nightscape of crickets and the loud croaks of a frog, precisely over there. An excited crowd, children shouting. A train chugs in from the right and comes to a halt across the platform.
Musical selections follow—an a cappella choir in some vast reverberant space, a New Orleans street band, a quartet of classical guitars—featuring shockingly expansive soundstaging, exact source positioning, and vivid ambience. Then Choueiri’s virtual voice is speaking in my left ear, my right ear, behind my head, and lastly he’s simulating giving me a haircut, with scissors snipping sides, top, and back.
Choueiri reappears at the door. “That was absolutely fantastic,” I tell him.
Spatial hearing in three dimensions depends on subtle differences in timing, sound level, and the shape of our heads and ears, among other factors. Binaural and even conventional stereo recording incorporates rich 3-D information. But “crosstalk” collapses the 3-D illusion: during playback, the left ear hears not only sound from the left speaker, but also some of the right-speaker sound, and the right ear likewise hears spillover sound from the left speaker.
A technique called crosstalk cancellation—processing the audio signal so that the left ear hears sound from only the left speaker, and the right, from only the right—can reveal the inherent 3-D sound in stereo. But crosstalk cancellation has always introduced audible spectral coloration. It’s this problem, applied to two-speaker playback, that Choueiri says he’s licked. He wrote a fiendishly abstruse 24-page technical paper explaining his theoretical work, and then spent several years coding and designing his Pure Stereo filter.
Manufacturers and producers sense enormous profits looming in 3-D audio for TV, cinema, and gaming. Compared with 3-D, the sales pitch goes, surround-sound systems are unwieldy and offer crude spatial definition. Princeton is now negotiating with various consumer companies to license Pure Stereo, and Choueiri also hopes to improve on hearing aids, which currently are not very good at pinpointing where sound is coming from.
In a sense, Choueiri’s adventures in audio represent a hobby that’s spun out of control. His real job is teaching applied physics at Princeton and developing plasma rockets for spacecraft propulsion. Visiting Europe to attend a conference in 2003, Choueiri decided on a whim to detour to Amsterdam and crash a meeting of the Audio Engineering Society, where several sessions explored the technical challenges of 3-D audio. “Within a few weeks, I read pretty much every paper in the field,” Choueiri recalls. Funding for his 3-D audio lab came from Project X, an initiative to encourage unconventional engineering research at Princeton.
Later during my visit, Choueiri invites me to his restored 1834 home near campus, where we spend hours sampling his enormous collection of vinyl LPs, reel-to-reel tapes, and high-definition audio files. Choueiri has a Jerry Garcia beard, a high forehead topped with stray tendrils of disorderly hair, and the dark-circled eyes of a nocturnalist. He puffs on a pipe while he roams the shelves.
“The most tiring part of stereo is the fact that the image spatially doesn’t correspond to anything that you ordinarily hear,” Choueiri tells me. “That’s what drove me to create this thing. Your brain is getting the right cues, and you relax. Your brain stops trying to re-create reality.”
Read the author's “Notes on the Search for Startling Innovations in 3D Audio” on The Atlantic's Technology Channel.
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