The Sound Book: The Science of the Sonic Wonders of the World

by Trevor Cox

  “Space, the final frontier,” announces James T. Kirk at the start of the first Star Trek episode. As the spaceship Enterprise flies past the screen, the voice sounds as though it was recorded in a very reverberant cathedral. I know space is a big place, but where are the reflections meant to be coming from? And anyway, space is silent or, to quote the catchy tag line from the 1979 movie Alien, “in space, no-one can hear you scream.” For an astronaut unfortunate enough to be caught outside the spaceship without a space suit, screaming to occupy the moments before asphyxiation would be pointless, as there are no air molecules to carry the sound waves. But Hollywood does not let anything as trivial as physics get in the way of a compelling soundtrack. The latest Star Trek film showed the outside of the soaring Enterprise accompanied by lots of powerful engine noises; the photon torpedoes sounded pretty impressive as well.

  When I think of the inside of a real spacecraft, I picture people floating serenely and gracefully in zero gravity. I met NASA astronaut Ron Garan in early 2012, when he had just returned from a six-month mission on board the International Space Station. He explained to me that the sonic environment in a real spacecraft is a long way from being serene. Even outside on a spacewalk (his previous mission had included a walk that lasted six and a half hours), there is no silence. Indeed, it would have been worrying if there had been, because it would have meant that the pumps circulating air for him to breathe had stopped working. Spacecraft are full of noisy mechanical devices, such as refrigerators, air-conditioning units, and fans. Theoretically, the noise could be reduced, but quieter, heavier machines would be expensive to lift into orbit.

  Studies on a single space shuttle flight found temporary partial deafness in the crew. Inside the International Space Station (ISS) it is so loud that some fear for the astronauts’ hearing.11 At its worst, the noise level in sleep stations was about the same as in a very noisy office (65 decibels). An article in New Scientist reported, “Astronauts on the ISS used to have to wear ear plugs all day, but are now only [required to] wear them for 2 to 3 hours per work day.”12 The need for earplugs, even for part of the day, indicates how hostile the soundscape is. Squidgy foam earplugs can reduce sound by about 20–30 decibels. The higher levels of carbon dioxide and atmospheric contaminants that exist at zero gravity in spacecraft might also make the inner ear more susceptible to noise damage.

  Outer space might be devoid of audible sound, but that is not true of other planets, and scientists have put microphones on spacecraft such as the Huygens probe to Saturn’s moon Titan to record it. As long as a planet or moon has an atmosphere—some gas clinging to the planet—there is sound. Microphones have the advantage of being light, needing little power, and being able to hear things hidden from cameras. Mind you, the audio recorded from Titan as the Huygens probe descended through the atmosphere is not very otherworldly. It reminded me of wind rushing by an open car window while driving on a highway. However, when I consider where it was recorded, almost a billion miles away from Earth, this mundane sound feels much more exciting.

  If a pipe organ were taken to Mars for a performance of Bach’s Toccata and Fugue in D Minor, the astronauts would find the notes coming out of their musical instruments at a lower frequency. The atmosphere of Mars would transpose the music to roughly G-sharp minor. The frequency of the note produced by an organ pipe depends on the time it takes sound to travel up and down the length of the tube. Because Mars has a thin, cold atmosphere of carbon dioxide and nitrogen, sound moves at about two-thirds the speed it does on Earth. The slower round-trip up and down the organ pipe produces a lower frequency. Given the toxic gases in the atmosphere, visiting astronauts would not be taking their helmets off to sing. But if someone did dare to do this, the voice would drop in pitch like the organ pipe, turning tenors into Barry White soundalikes. Unfortunately, the sexy voice would not carry very far, because Mars’s thin atmosphere is almost a vacuum.

  Venus has a very dense atmosphere, which would slow down the vibration of the astronaut’s vocal folds (vocal cords) and lower the pitch of the voice. However, sound travels faster in the Venusian atmosphere, which would make the resonances of the mouth and throat rise. As a result, the astronaut’s voice would sound squeaky, as happens when someone talks after breathing helium. Tim Leighton, from the University of Southampton, suggests that together, these effects would make an astronaut sound like a bass Smurf.13

  Although sound levels in the International Space Station have been reduced enough that they probably no longer pose a risk to hearing, noise can affect health in other ways. And it is not just astronauts who should be concerned. For example, someone whose sleep is disturbed by airplane noise is more likely to be tired, irritable, and less effective at work the next day. If we are exposed to high levels of noise, our bodies will produce more stress hormones in the long term that might elevate blood pressure and increase the risk of heart disease.14 Removing noise is therefore good for us, but is a strong dose of quiet better? Should we be seeking out complete silence?

  One day at the office—that is, our anechoic chamber at Salford University—as the BBC tried to measure the footfall of a centipede, sound recordist Chris Watson suggested I should visit a flotation tank, a dark isolation chamber where you float in very salty water and experience sensory deprivation. And when better to experience that than a few days after hearing silence in the Mojave Desert? I headed to Venice Beach, a bohemian district of Los Angeles famous for its skimpily dressed in-line skaters, outrageous street performers, and kooky poseurs. My appointment was after dark, when the place feels less free-spirited and distinctly more dangerous.

  I went to a tatty, closed shopping mall, and the attendant opened up the shutters to let me in. The tank was in a small shop at the back. He showed me around, giving detailed instructions on what to do, before asking me to sign a lengthy disclaimer. He then announced that I could stay as long as I wanted because he was leaving. I was told to let myself out, making sure I closed the shop door securely behind me. This was unnerving. What would happen if I fell asleep? What if I could not get out? Was I going to be stuck in a flotation tank overnight? With trepidation I got undressed, stuck in my earplugs, showered, and wandered over to the tank.

  From the outside, the chamber looked like a giant industrial fridge, made of metal to keep noise out, about 2.5 meters (8 feet) long, 2 meters (7 feet) high, and 1.5 meters (5 feet) wide. I climbed in, shut the door, and lay down in the body-temperature, shallow, salty water. The buoyancy of the brine kept me well afloat, but the angles between my head, neck, and back felt unnatural, and it took time for me to get comfortable. It was pitch-black; it did not matter whether my eyes were open or closed, there was nothing to see. Lying naked in the dark, unable to hear external sounds, and in a closed, rundown shopping mall, worrying thoughts besieged me. Was the attendant a new age version of Sweeney Todd?

  I turned my mind to more pleasant things and tried to relax into the experience. Provided I lay still and did not splash about, I could perceive nothing from outside. I could hear the internal high-pitched whine I had noticed in the desert, but after a while it disappeared, returning only intermittently. There was also a low-frequency, pulsating sound that sometimes seemed to make my head wobble. This was pulsatile tinnitus, where the sensitive hearing system picks up the rhythmic pumping of blood. It’s similar to the sensation you get when the heart starts pounding during intensive exercise. Normally, this blood movement is quieter than the everyday external sounds passing down the ear canal, but in the flotation tank with earplugs, this pulsing sign of life became audible. I heard it only occasionally, and most of the time I could hear nothing at all. To appreciate this total silence, I had to shut up the voice in my head and stop myself from listening for sounds. This is not easy to do, because the brain constantly directs attention in anticipation of hearing something. In a neuroimaging study, Julien Voisin and colleagues found increased activity in the auditory cortex during the silence before a sound was heard.15


  The effect of cutting off both hearing and vision, and the feeling of the hot, salty water on my skin, made me very aware of touch. After a while I got the impression that my legs and arms had disappeared and my feet and hands were detached from my body. They felt slightly numb, like the sensation you get just before pins-and-needles sets in. It is hard to articulate the sound experience because it was all about an absence of hearing. This was probably the nearest to a truly perceived silence I have heard, because for long periods my sense of hearing seemed to be completely missing, to the point that my only sense seemed to be touch.

  I decided it was time to finish; I struggled to my feet and groped around for the door handle. Outside of the chamber I checked my watch and was flabbergasted that I had been floating for two hours! I showered, dressed, let myself out of the shop, and sat in my car feeling very weak and queasy, probably because I was badly dehydrated. The flotation tank is supposed to help with stress management by lowering levels of cortisol, but in my shaky state I was not at all sure it had worked for me.16

  Going to the countryside and getting some peace and quiet is meant to be good for us. But rural places are usually far from silent. Within a crowded and intensely farmed country, it is difficult to escape the sounds of agriculture and human activity. Media stories about newcomers to the countryside complaining about noise appear each year like perennial weeds:

  The mayor of a French village has forbidden complaints about farmyard noises, in a pre-emptive strike against a growing number of urban newcomers prepared to sue for their “right” to rural peace. City dwellers intending to join the 300 inhabitants of Cesny-aux-Vignes, 12 miles from Caen in Normandy, have been asked to cohabit with crowing cockerels, braying donkeys or chiming church bells “without complaint.”17

  But those people aren’t alone in imagining the ideal countryside through rose-tinted ears.18 I conjure up pastoral sounds: the bleating of sheep in fields, the trickle of water running down a stream, and the thwack of leather on willow at a village cricket match. I am not a particularly nostalgic person but, rather startlingly, I have just painted a scene from a P. G. Wodehouse novel, tales of England from a hundred years ago, with the bumbling aristocrat Bertie Wooster and astute butler Jeeves.

  Take a moment to think of your ideal rural soundscape; what would you like to hear? I would be surprised if you picked complete silence, because most people go to the countryside to feel connected with nature. Gordon Hempton, a sound recordist and acoustic ecologist from Washington State, has been campaigning for the preservation of natural silence, which “is as necessary and essential as species preservation, habitat restoration, toxic waste cleanup, and carbon dioxide reduction.”19

  Gordon Hempton claims that there are very few remaining quiet places in the US, even though the country has large tracts of empty land. True freedom from man-made sounds is surprisingly hard to achieve because of the web of flight paths that crisscross the sky. Hempton has named one niche that is free from aircraft noise as “One Square Inch of Silence” and says this “is the quietest place in the United States.”20 It is located in the Hoh Rainforest, in Olympic National Park, Washington State. But there is not a complete absence of sound. Although the location is free from man-made noises, there are plenty of natural sounds to listen to in this enchanting rainforest. The lush, green canopy of ancient coniferous and deciduous trees with mosses and ferns blanketing the surfaces is home to noisy animals and birds, and the high level of rainfall produces lots of river noises. Imagine if it were truly silent, so the rapid staccato notes of the winter wren were missing and no Douglas squirrel was crying “pillillooeet.” This would be a barren and lifeless place.

  Murray Schafer, the pioneering acoustic ecologist who evangelizes about ear cleaning, praises rural settings and calls them a “hi-fi soundscape.” A good-quality audio system reproduces sound with little or no unwanted noise. This fact led Schafer to define a hi-fi soundscape as being a place where the hearing system is not overwhelmed by undesirable noise, making useful, relatively subtle sonic information more audible. In contrast, he defined a lo-fi soundscape as one where individual sounds are masked by the rumble of traffic and other man-made noises.21

  The US National Park Service has a policy that states, “The Service will restore to the natural condition wherever possible those park soundscapes that have become degraded by unnatural sounds (noise), and will protect natural soundscapes from unacceptable impacts.”22 The Campaign to Protect Rural England (CPRE) claims that half the people visiting the countryside do it to find tranquillity.23 Access to tranquillity has been shown to reduce stress.24 (The three competing theories as to why natural sounds might be good for us were outlined in Chapter 3.) Research commissioned by the CPRE found that seeing a natural landscape, hearing birdsong, and seeing the stars were the top three things contributing to a sense of tranquillity. Unwanted features included hearing constant traffic noise, seeing lots of people, and urban development. As these findings show, tranquillity is not just about sound; it includes being calm and free of disturbance, including consideration of how a place looks. It requires our senses to be in harmony, and not to have competing and conflicting stimuli.

  In science, the different senses are often studied in isolation, but our brains do not take such a demarcated approach. Although we sometimes use different regions of our brains to process and interpret signals from our various senses, the overall emotional response comes from an aggregation of what we see, hear, smell, taste, and touch. Michael Hunter, from the University of Sheffield, and collaborators have shown how the brain handles sensory inputs in tranquil and nontranquil places using a functional magnetic resonance imaging (fMRI) scanner.25 Ingeniously, they used an ambiguous sound recording in all the tests (waves crashing on a beach sound remarkably like light road traffic) and just changed the picture to make people think they were listening to something different. The natural scene of the beach increased connectivity between the auditory cortex and other parts of the brain. The increase in connectivity did not happen with the man-made highway. The results show that what we are looking at affects which neural pathways are used to process sound. When we’re evaluating tranquillity, we must consider sound and vision together.

  The author Sara Maitland has gone to great lengths to find tranquillity and solitude: “Chosen silence can be creative and generate self-knowledge, integration and profound joy.”26 She moved to a remote cottage, cut off communication with others, and removed the TV, clothes dryer, and as many other noisy appliances as she could. Maitland writes about the sense of spirituality that her silent existence has given her. Others have also referred to rural tranquillity in hushed, almost reverential language. Indeed, surveys have linked quiet, natural places and a sense of spirituality.

  A tranquil soundscape has a quality and emotional connection similar to that found in churches: people become very sensitive to the sounds around them, but not in a stressful way.27 Maybe this sense of spirituality simply reflects the reduced cognitive load on the brain, which experiences less stress when processing the calmer soundscape. To keep our hearing open to possible signs of danger, our brains have to constantly work to suppress unchanging noises, such as the perpetual drone of traffic. This situation is not conducive to finding a relaxed and spiritual sense of well-being.

  The CPRE has even quantified tranquillity, publishing brightly colored, blotchy maps of England that define areas by how tranquil they are. Researchers calculated a tranquillity index by working out what people might see by measuring lines of sight to natural and man-made features, and also what they might hear through predictions of noise levels from roads and aircraft.28 When I looked up my home city on the map, I found it to be a sea of red, signifying no tranquillity. Then my eye was drawn toward dark green areas farther north, just below the Scottish border, indicating large tracts of tranquil countryside.

  Somewhere in the green areas was the most tranquil place in England, and I decided I wanted to visit it. But when the origin
al research had been published a few years earlier, the CPRE had been coy about the exact coordinates of the most tranquil place, not wishing it to be ruined by visitors. So I was surprised and delighted when I was granted access to the original mapping data so that I could pinpoint the location just outside Northumberland National Park, near Kielder Forest.

  The place would not be easy to reach, because by definition it was far from buildings, infrastructure, and roads. A few months after returning from the desert, I sorted out the logistics and started by cycling as close as possible on the nearest road. It was the start of autumn, and I was either too cold in the deep shadows cast by conifer forests, or out of breath and too hot climbing up hills in full sun. I traveled through countryside typical of northern England: rolling hills with fields being grazed by sheep and cattle bordered by dry stone walls. As I gained more height (the most tranquil place is almost at the top of a hill), I entered scrubby moorland with army tanks in the middle of a firing range. I now realized why this place has very little human infrastructure on civilian maps. Strange that the place rated as being very tranquil is where the gunners of fighter planes are often trained.