I Can Hear You Whisper Read Online Free PDF Page B

decibels.
    The number of cycles in each sound wave, whether it rises and falls in tight, narrow bands or loose, languid swells, determines its frequency, which we hear as pitch and measure in hertz (Hz). The range of normal hearing in humans is officially about 20–20,000 Hz. Just how astonishing that range is becomes clearer when you compare it to what we can do with our vision. The visible light spectrum encompasses one octave (a doubling of frequency, so violet light has roughly two times the frequency of red), resulting in 128 noticeably different shades of color (these are literally measured in a unit called “just noticeable difference” or JND), although in fact there are far more variations than the eye can see. Hearing, on the other hand, encompasses nearly ten octaves with five thousand just noticeable differences. What sounds too good to be true usually is. Only small children really hear that much. Hearing sensitivity declines with age, and what most adults hear spans about half the possible range, 50–10,000 Hz.
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    Somewhere along the way, some part of the sequence of hearing was not working for Alex. Jessica and Tracey were trying to figure out what. Having two audiologists was going to make a difference in the reliability of the results, because testing children takes as much art as science. Kids get cranky and tired. They don’t pay attention. If they’re very young, they can’t tell you what they hear. The solution is for one audiologist to run the test and the other to play with the child. Both watch like hawks for signs of response and compare notes. Although there are more direct physiological tests of hearing, behavioral testing is still essential because it’s a measure of the results of the entire system. It’s like the difference between seeing if a dishwasher turns on and seeing if the dishes come out clean.
    A quick immittance test—a puff of air through the canal—showed that Alex’s right ear was still full of fluid. No air, and therefore no sound, was flowing through. His left ear, however, was not fully blocked. By this point, the fluid alone was not enough of an explanation. “Fluid doesn’t make them not talk,” Jessica explained. “They might be slower or like louder noises,” but children won’t fail to talk entirely.
    We moved on to testing in the booth. With Tracey running the audiometer and Jessica enticing Alex with stuffed caterpillars eating toy fruit and toppling block towers, they worked their way through loud and soft sounds of every frequency. Alex had to feed the caterpillar or add a block every time he heard a sound.
    Watching the test was an anxious experience, like watching a child readying to catch a pop fly when the game hangs in the balance, or willing her to perform a difficult piece at a crowded recital. Only more so. You observe and your nerves jangle.
    As Karen had explained to me, hearing tests create an audiogram, a graphic representation of what a person can hear, by drawing a line (two, actually, one for each ear) along the threshold of the softest detectable sound. The x-axis charts low to high frequency from left to right. Decibels run down the y-axis, getting louder from top to bottom. (Some audiograms reverse this and put the louder sounds at the top.) There’s a complication, though. Sound is deceptive. When we listen, we tend to think we hear just one pitch, but there’smore going on than that. Daniel Levitin, in
This Is Your Brain on Music
, uses the analogy of Earth spinning on its axis, traveling around the sun, and moving along with the entire galaxy—all at the same time. When we call a note on the piano middle C, we have identified the lowest recognizable frequency, known as the fundamental frequency, but there are mathematically related frequencies called harmonics or partials sounding above that at the same time. Our brains respond to the