Beyond the cocktail party – headphones simulate selective ability of human ear
The information age brings us a blinding amount of data. Our ears may prove to be a better guide than our eyes.
HAVE YOU EVER BEEN at a cocktail party where dozens of people are talking all around you, yet without turning your head you can tune in to any conversation in the room?” asks Erik Tarkiainen, an acoustical engineer at Sonic Perceptions in Norwalk, Connecticut. Even though many voices bombard our ears, we manage to focus on just one, determine where it’s coming from, and even judge how far away it is. Acoustical engineers call this phenomenon the cocktail-party effect, and they’re starting to harness it for a variety of applications.
“In this age of data overload, the trick is coming up with new ways of interpreting information,” says Tarkiainen. “Hearing is a sense that has been overlooked.” Most of the improvements in information technology are based on sight, such as computer-graphics displays that allow users to visualize data and see the whole picture. But such visual improvements are not always enough for, say, an air traffic controller trying to land ten planes approaching from different directions. Two planes flying one above the other appear as superimposed bugs on the computer monitor, and there’s no way to see whether they’re passing peacefully or about to crash.
So HEAD Acoustics (the German company for which Sonic Perceptions is the North American representative) has designed a “binaural mixing console”–computer hardware that makes a noise sound to a person with headphones as though it’s coming from a particular place. Several voices heard at once through normal headphones sound like meaningless jumbles of words. But if each voice is assigned a position, the cocktail-party effect comes into play: suddenly the listener can easily tune in to any one of them. Our overburdened air traffic controller, for instance, now has audible as well as visual clues to judge whether two planes are closing in on each other.
Tarkiainen’s equipment places sound the same way the human ear does. When a gossiper is talking behind and to the left of us, we hear the voice in that position thanks mostly to our pinnae, the fleshy outer funnels that we call ears. The gossiper’s voice creates sound waves of many different frequencies, and as they bounce off the pinnae and rebound into our inner ears, some wavelengths are amplified while others are diminished. If that gossiper should take a few steps forward, different sets of frequencies will be amplified or diminished. Through a process still unknown to neurologists, our brain recognizes how such subtle frequency changes translate into “behind us” or “high to the left.”
The problem with headphones is that sound is transmitted straight into the inner ears, so the pinnae don’t have a chance to do their job. The binaural mixing console must therefore modulate sound electronically.
A hodgepodge of all audible frequencies of sound, or “white noise,” is recorded using an artificial head that has plastic pinnae and a microphone in each of its inner “ears.” To determine how our pinnae would alter a noise, say, in the eight o’clock position, 57 degrees high, sound is recorded from that location, and the amount the pinnae amplify or diminish each wavelength is measured. HEAD Acoustics has analyzed sound at points every two degrees around its artificial head; these modulations can then be applied to, say, a pilot’s voice. The computer makes the voice move smoothly from point to point, giving the listener the impression that the pilot is swooping in toward the southwest runway.
HEAD Acoustics thinks the technology will have applications well beyond the air traffic control tower. Future surgeons, for instance, could listen to the outputs of several machines at once, and if the cardiogram reading was the most critical, its sound would come from directly in front of the doctor. A tank driver could hear his commander alerting him to an approaching enemy, and the voice of warning would be located in the very direction of the threat. Detroit’s Big Three carmakers are using cocktail-party-effect microphones to measure which sounds are most disturbing to a car driver. And the applications to the music industry are obvious: headphone listeners could come closer to experiencing the feeling of being at a real concert.
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