Sounds Realer Than Reality

3 June 2002 (All day)

Bag of tricks. An assortment of Foley props.

Hollywood may soon be able to craft acoustic illusions that sound even better than the real thing. New experimental findings reveal that scientists can generate imitations of real-life sounds significantly more convincing than actual recordings of the events they are intended to mimic--results that also shed light on how the brain extracts meaning from experiences.

Sound effects technicians, known as Foley artists after Hollywood pioneer Jack Foley, create the noises that bring to life the soundscapes of radio, film, and television. Because giant explosions and other, less extraordinary activities often prove impractical to record in a studio, Foley artists traditionally relied on props. For instance, the sound of a crackling fire can be imitated by twisting cellophane, and squeezing a box of cornstarch can duplicate the sound of footsteps in snow.

Because traditional Foley effects often possess very different acoustic characteristics from their real-life counterparts, experimental psychologists Laurie Heller and Lauren Wolf at Brown University in Providence, Rhode Island, wanted to find out which components are key in recognizing a sound. First, they had 17 volunteers listen with headphones to familiar sounds, such as breaking glass, paired with lab-generated Foley imitations. A few Foley effects fooled the listeners, but in most cases they could pick the real thing.

Next, the researchers attempted to create sounds that were more convincing than the real ones by digitally manipulating the three most successful Foley effects: "walking on mud" (squishing wet crumpled newspaper), "walking in leaves" (running fingers through cornflakes), and "crushing eggshells" (squeezing folded sandpaper). More than 70% of the time, listeners rated these new sounds as more convincing than the real ones, the researchers reported 3 June at the Acoustical Society of America meeting in Pittsburgh. They say that enhancing the slow-moving wave components of a sound--known as its "envelope"--results in better perception of actions such as walking. But augmenting the faster acoustic portions of a sound apparently helps people identify what materials are involved in an event. Heller and Wolf say the findings are a step toward understanding what acoustic clues the brain uses to interpret sounds.

And how real do the findings sound? "I find the early data quite promising," says experimental psychologist Virginia Richards of the University of Pennsylvania in Philadelphia. But she says the team will need to investigate a wider variety of sounds to show convincingly what information the brain really uses to decide if a sound is real.

Related sites
The researchers' lay language presentation
The Art of Foley

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