or from body language, for example) and those further away that play a role in triggering emotions and empathy. The sheer complexity of the way our brains process sound allows them to do some incredibly impressive feats. “The processing part of our brains is basically a pattern recognition machine,” says Stephen Entwistle, Dynaudio’s chief engineer, acoustics. “This is why we can localise exactly where a sound is coming from even with our eyes shut. Our brains can figure out the size of a room from the way sound reflects off the walls and objects in it, and recognise the voices of people we know on the phone even if they’re distorted. They filter interfering sounds and even replace fundamental notes from music if they’re missing.” But it also means that our brains can be tricked through the use of auditory illusions. The most familiar of these psychoacoustic effects is the use of stereo to fool our brains into believing a sound is coming from a 3D space rather than a left and right speaker. Where it’s at “With a really good speaker, you can localise sounds with incredible accuracy,” says Entwistle. “At Dynaudio we evaluate our speakers in stereo even though many others follow guidelines from the AES (Audio Engineering Society) to use mono because it’s easier to get a consistent result.” Entwistle and his colleagues use a wide range of music to help them assess the performance of their speakers during development, but he points at two particular favourites that make use of the ability to recreate 3D sound effects. The first words of Vogue by Madonna sweep across the listener before a click appears high on the left. The Ballad of Bill Hubbard by Roger Waters features a dog barking behind and to the right, before a radio appears on the floor to the left. “A lot of this stereo imaging and immersiveness has to do with the fundamental tracking that appears when you put a properly integrated subwoofer onto a speaker,” says Entwistle. “The low-frequency information seems to help our brains process the other information in some way.” Close your eyes and see There is some evidence that depriving ourselves of our other senses, such as sight, can also alter our experiences. A small study conducted by researchers in Israel found that when volunteers closed their eyes while listening to clips of music from films, they experienced a greater emotional response. They also showed greater activation in a Magazine 04 57
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