Everyday Mysteries
Audio recording is one place where it's becoming increasingly difficult to say whether noise is a force for good or evil. The vinyl phonograph record is noisy. Ticks, pops, scratches, and hiss all intrude. However, a very soft musical passage can still be discerned, even when its sound is quieter than all of that unwanted noise. Compact disks, on the other hand, are silent. Most CDs are recorded digitally; music becomes binary digits, long strings of zeros and ones. In the quietest sections, the sound level fades until there is no more digital information, and it cuts off. For just that reason--the arbitrary cutoff of sound--stereo snobs have for years argued that the CD is harsh and unrealistic.
Now, engineers are finding that by adding noise, they can improve CD sound. It's called dither, a low-level noise, about the volume of one digital bit (the smallest significant amount of recordable digital information), which is mixed into the sound being recorded. The addition of dither noise pushes low-level sound signals above the one-bit threshold, allowing a CD to capture what before would have been distorted or lost altogether. Ken Pohlmann, a digital expert at the University of Miami School of Music, says a CD recorded without dither captures a 95-decibel range from loudest to softest. With dithering, the range becomes 120 decibels.
Noise may play a similar, paradoxically useful role in visual perception. Enrico Simonotto of the University of Genoa shows research subjects a video on a computer monitor; the image is contrastless and contains very little apparent detail. To most people, it looks like a nearly blank screen. But when he introduces random "noise"--minute grains of color, almost like adding snow to a TV picture--viewers recognize what the image is, a human face. As the noise increases and the image begins to resemble a pointillist painting, features such as a beard and eyeglasses become apparent. Scientists studying this phenomenon of "stochastic resonance" believe the noise may help the brain's neurons detect weak signals.
Clearly, no one suggests rubbing a record with sand or watching TV without an antenna. But as science learns more about how we see and hear, noise seems to be a lot more than just, well, noise.
WHY DO WE HICCUP? The medical literature lists more than 300 causes of hiccups. So-called everyday hiccups can result from inhaling too much air, eating spicy foods, or drinking too rapidly. Excessive smoking, laughter, and fatigue all make the list.
But those in search of an explanation for why the body reacts to food, drink, air, or the Three Stooges that way will take little comfort from the fact that No. 1 on the list of causes is "no known cause." Particularly odd is that hiccups seem to be almost unique to humans as a species. "It's pretty rare to see hiccuping animals," says Dr. Charles Welford, a clinical assistant professor at the University of Illinois College of Medicine at Rockford. Welford has studied every article on hiccups published in three languages since 1860 in a so-far-unsuccessful quest for an explanation of the phenomenon.
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