The Sound Book: The Science of the Sonic Wonders of the World (11 page)

A
year after going to Wayland's Smithy, I joined thirty other people at sunrise of a very cold spring day to hear birds singing the dawn chorus at the Yorkshire Sculpture Park in England. Our guide, Duncan, was a typical bluff and taciturn Yorkshireman who was not going to waste ten words where one would do. “How do you know that's a great tit,” I asked. “You just know. Years of listening and watching,” was the straight answer. We stood among the trees and sculptures, with bluebells lighting up the undergrowth, all being brought to life by rays of early-morning sun, and just listened. As Duncan might have said, we had signed up for a dawn chorus walk, and listening to birds was all we were going to do.

First I took in the general soundscape. Since it was spring, the birds were in full voice, with song surrounding us from all sides. Duncan was right not to give us expansive descriptions, because being forced to stand and just listen was revelatory, bringing home to me the sheer complexity of the dawn chorus. I tried estimating how many birds were singing and where the sounds were coming from. I tried to pick out individual calls, like a conductor listening for a particular orchestral instrument. In the distance, there was the honking of noisy geese from the lake at the bottom of the hill; they seemed to be constantly screaming. Higher up the slope was the occasional cooing of wood pigeons. In the direction of a rusting sculpture, rooks were cawing their signature call. And all around, songbirds were tweeting and warbling. I picked out one bird singing a powerful short cascade of notes; Duncan identified it as a robin. Now, robins visit my garden all the time, but I had never realized how rich their song is. Chiffchaffs, nuthatches, and chaffinches—how could I have overlooked the diversity of this natural orchestra and just lumped all these little instrumentalists into one big category labeled
birdsong
?

The scientific literature on noise extends even less consideration to individual creatures. A single category contains not only bird calls but also every other natural sound. And there are only two categories:
natural
and
unnatural
. Common sense holds that natural things are good for our health and to be encouraged, and unnatural sounds are harmful and to be abated. But this is an oversimplification that researchers such as Eleanor Ratcliffe, an environmental psychologist from the University of Surrey, are starting to pick apart. Eleanor is researching people's responses to birdsong. In a survey, she found that although birdsong was the most commonly mentioned natural sound, in about a quarter of the responses she read it was unwelcome. For instance, one person complained about the unpleasant, raucous, cackling cry of magpies, partly because magpies have been unfairly blamed for there being fewer songbirds nowadays.
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Eleanor has been running other experiments to see whether more pleasant bird calls may be better than others in helping people de-stress. In one test, the call of a small, olive green forest bird from New Zealand, the silvereye, was rated as most likely to help people relax and recover from mental fatigue. The silvereye sings an archetypal, pretty songbird warble. In contrast, the ugly screech of a jay was rated as less helpful for stress and mental fatigue.

Animal calls are at the heart of our relationship with the natural world. The sounds of insects, birds, and other animals are parts of our memories—evocative of time, place, and season. For me, the croaky “aah” of a rook immediately conjures up images of a churchyard in an English village at twilight, where the birds are settling down to roost. The rhythmic buzz of crickets brings back fond memories of balmy evenings camping in the south of France. When I hear the horrible scream of foxes in heat, I remember waking up once with a start, convinced that a baby was being murdered outside my bedroom window. Many natural sounds are unpleasant like the fox's cry, but could some of these ugly calls be good for us?

Documentary directors portray the natural world as though vision is the only important sense. Sadly, in natural-history television programs the wildlife sounds are virtually inaudible; instrumental mood music and pictures dominate. I asked natural-history sound recordist Chris Watson about this. If you have seen any recent BBC natural-history programs, chances are that Chris recorded some of the wildlife. In his soft, northern English drawl, he explained to me that the music is slapped on to manipulate mood: “[It's] so badly done, it's so omnipresent and intrusive, it's like being injected with steroids.”
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But this playing down of natural sound is artificial. How often have you heard wildlife you did not see, because it was difficult to spot or hidden from view? And how did that sound make you feel?

This may not come as a great shock, but science seems to demonstrate that nature is largely good for us. One well-known study showed that patients after gallbladder surgery were discharged from the hospital sooner if their bed had a view out of a window rather than facing a brick wall.
³
Laboratory studies have shown that exposure to nature aids recovery from mental fatigue. Psychologist Marc Berman and collaborators assessed their subjects' mental abilities, for example, by getting them to remember and recount a sequence of digits in reverse order. The subjects then went for a walk in a park or in downtown Ann Arbor, Michigan. After the break, the subjects were retested, and those who had experienced nature outperformed those who had gone downtown.
⁴

Nature can also aid recovery from stress. Roger Ulrich and collaborators examined the responses of 120 undergraduate volunteers as they watched a couple of videos.
⁵
All of the students watched the same first video, which was designed to create stress, depicting accidents in a woodworking shop and including serious injuries, simulated blood, and mutilation. For the second video, half of the students viewed a depiction of a natural setting, and the other half viewed an urban setting. During this second video, the students were asked to rate their affective state while researchers took physiological measurements to gauge how much they were sweating. The students who watched the nature movie recovered more quickly from the stress induced by the accident video than did those who watched the urban recovery film.

Unfortunately, very few studies in this field have focused on the role of acoustics. One rare exception is the study by Jesper Alvarsson and colleagues. They stressed forty people with tricky mental arithmetic tasks. They then allowed the subjects to recover while listening to recordings such as fountains and tweeting birds, or traffic noise, to see how different sounds changed stress recovery. Results were inconclusive, however. Only one of the physiological measures, the amount of sweating, responded positively to the natural sounds.
⁶

There are three competing theories as to why nature might be good for us. The first is evolutionary; it suggests that a preference for natural things evolved to encourage us to seek out fertile natural environments where we could find food. The second is psychological and suggests that nature stops us from being too self-absorbed and having negative thoughts, by giving us a sense of belonging to something “greater than oneself.” The third theory says that restorative natural places have “soft fascination,” meaning that there are captivating yet calming features to look at, such as clouds, sunsets, and the motion of leaves in a breeze, and that this soft fascination helps achieve cognitive quiet.
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These theories can help explain our reactions to natural sounds that are aesthetically pleasing. But what about those that aren't?

W
atching westerns as a child, I always felt that the rhythmic chirring of crickets was ridiculously loud. How could the cowboys sleep with that racket going on? It seemed unbelievable that such a small insect could make such a loud sound.

I got the opportunity to ask some top sound people from Hollywood about this one sunny afternoon, as we sipped margaritas alongside a clear blue swimming pool in Los Angeles. Myron Nettinga is an Academy Award–winning sound mixer and designer. Gregarious, enthusiastic, and fixed with a permanent smile, he explained that insects really are that loud in the midwestern US. But what he said next is what really grabbed my attention. In choosing a cricket to accompany the cowboys eating beans around the fire, a sound designer does not pick out any old recording, but must find the one that portrays the right mood to accent the film's emotional narrative. Myron explained that for a scene about a lazy, calm night in the country, he might pick a soothing cricket, “but hey man, if a guy is creeping around the back of the house looking to jump some people, then all of a sudden there's a cricket and he's agitated and he's a little nervous, and he's stopping and starting.”
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Myron's choice depends on the rhythm of the cricket chirrs and the abruptness with which each sound starts.

While cricket calls vary between species, the various buzzes and chirps all start with stridulation, in which the insect rubs its body parts together.
⁹
The snowy tree cricket sounds like a quiet trill phone as it rubs its wings together in a rapid scissoring action, swiping a hardened scraper from one wing against the stridulatory file—a structure that looks like a saw blade when magnified under an electron microscope—on the other wing. It is like a tiny version of a scraper percussion instrument you might have played in elementary school. Every time the cricket's scraper hits one of the teeth of the stridulatory file, a small impulsive sound is made. The pitch of the trill depends on how fast the scraper is pulled past the teeth. Typically a tooth on the stridulatory file is hit by the scraper every half millisecond, creating a frequency of 2,000 hertz, a typical pitch for someone whistling.

In a recording I have of a snowy tree cricket (Figure 3.1), the insect draws the wings across each other eight times before pausing for about a third of a second and then doing it again. The snowy tree cricket is nicknamed the
temperature cricket
because its call speeds up as the insect gets hotter. You can estimate the temperature (in Fahrenheit) by counting the number of chirps that happen in a quarter of a minute and then adding 40.
¹⁰

Figure 3.1 The call of the snowy tree cricket.

Given this well-known correlation between temperature and rhythm, sound designers like Myron might choose a slower-chirping, colder cricket to evoke calm (even if the film scene depicts a warmer, lazier night). A hotter cricket sounds more urgent, like a trill phone that demands to be answered, with the chirps closer together and starting more abruptly.

On its own, the stridulation does not make a very loud sound, but each tiny impulsive vibration causes parts of the wing to resonate and amplify the sound. This is similar to how a violin works. The bow vibrates a violin string, which is very quiet on its own. But the string's vibration travels through the instrument's bridge to the wooden body, which has a large surface area and radiates a much louder sound.

The periodic cicada, another insect that uses stridulation, sounds more like a bird than any insect. The cicada's slow, two-tone call starts with an unpleasant, high-pitched screech that lasts a couple of seconds before the frequency drops by about an octave down to a lower, breathy note.
¹¹
The cicada makes short impulses by rapid muscle movements that deform and release tymbal membranes underneath the folded wings—a bit like deforming an aluminum can with your finger. The clicks created when the membrane deforms or pops back are amplified by the resonance of air in the insect's abdominal cavity.
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While the cicada's dissonant call is terrifying in its own way, I suspect the call is too unusual for sound designers. If you are trying to pull people in and make them feel as though they are really in a film scene, sounds must not be so unusual that they draw attention to themselves. As Myron put it, “You don't want to let them see the magician behind the mirrors . . . You want to make it seem . . . that they're there.”
¹³

In Bowie, Maryland, near Washington, DC, ash trees filled with a brood of male cicadas can exceed 90 decibels, well above safe workplace levels.
¹⁴
Such dense congregation of cicadas happens only every seventeen years, because of the cicadas' long life cycle. The biggest and most common cicada in the Maryland brood was
Magicicada septendecim
, which, according to a report in a local paper, “sounds like a giant [w]eed-whacker or sci-fi spaceship.” The loudest cicada in the trees was another species,
Magicicada cassini
, which produces “a harsh screeching noise like the sound of a million baby rattles.”
¹⁵

Famous ocean explorer Jacques Cousteau might have celebrated
The Silent World
back in the 1950s, but actually the underwater environment is far from quiet. Water boatmen (
Micronecta scholtzi
) use stridulation to make calls that sound like the rhythmic chirring of crickets.
Micronecta scholtzi
is said to be the loudest aquatic animal relative to its body length. Though only a few millimeters (about a tenth of an inch) long, it can be audible from a riverbank.
¹⁶
The discovery that the insect rubs a ridge on its penis against corrugations on its abdomen to initiate the sound made headlines—a rare tabloid triumph for entomological anatomy.