We hear a doubling of frequency as an octave, so our 20-20,000 Hz audible range spans just under 10 octaves. By contrast, the entire visible light spectrum is just one octave. Hearing degrades with age and gets damaged by exposure to loud noise, so many people can no longer hear the full audible spectrum. I know this all too well: after years of drumming in bands, I can’t hear anything above 12 kHz and I have tinnitus, a ringing sound in the ears that becomes quite evident if I sit in very quiet places. We’ll look at hearing in more detail in Chapter 3.
Sound always requires a medium to carry it. In most cases the medium is air, though you may be surprised to learn that sound travels almost 5 times as fast, and much further, in water. To understand how sound works in a medium, imagine a densely-packed crowd standing in a room. If you were to barge into someone on one side, the domino effect will end with someone on the other side of the crowd falling over. This is exactly how air carries sound waves; the air molecules bump into one another, and the wave propagates. Without a medium, sound simply can’t travel, so it was perfectly accurate for the promoters of the film Alien to say “In space no-one can hear you scream.”
Most sounds we hear are composites of many frequencies. Usually there is a fundamental, which in music we hear as the pitch, plus overtones, which are what give the sound its particular timbre or colour. Overtones create timbre: they are how we distinguish a flute from a trumpet playing the same note, or how we instantly recognise a familiar voice. Tuneful overtones with frequencies that are perfect multiples of the fundamental are known as harmonics.
Harmonics exist in many of the sounds we encounter, even though we are largely unaware of them. I once had a revelatory experience with harmonics during a week-long workshop with the great American overtone singer and teacher David Hykes. The practice of modulating and filtering the harmonics of my own singing voice (which is how overtone singers are able to sing 2 notes at once) had an effect on my ears, sensitising them to harmonics in general. I got into the car at the end of the third day of the workshop and turned the ignition key – and was astounded to hear all the harmonics of the engine noise. This was the auditory equivalent of seeing a rainbow, where all the constituent colours of light become visible, and it was just as beautiful. Sadly, as the weeks passed, the ability faded and now I no longer hear those harmonics, though I know they are all there. This experience is what gave rise to my listening exercise of savouring, which you will learn in Chapter Four.
Many physical objects have a property called resonance, which means they are particularly responsive at one or more frequencies. You may have experienced something similar in some badly designed rooms, where there’s a booming effect at particular frequencies when people speak. A bell is a perfect example: when struck, its resonance emphasises a certain set of frequencies, which we hear as the note of the bell and its harmonics, while it effectively filters out all the other possible pitches. Most musical instruments make use of this property to create notes, and this natural physical effect may well have been what led ancient humans to create music in the first place. Resonance can be destructive too: soldiers break step when crossing bridges in case the tempo of their marching matches the resonant frequency of the bridge, which can create oscillations powerful enough to destroy the structure completely. When the beautiful Millennium Bridge in London opened in 2000 it had an effect nobody had forecasted: its resonance created little vibrations that entrained the people walking across to fall in step, setting up a feedback loop that ended up with the whole structure wobbling alarmingly. The bridge had to be closed and £5 million of special damping equipment installed before it could be reopened.
Some sounds also have rhythm and tempo. Music is the most obvious example, but it’s also true of many electromechanical sounds, from manufacturing machinery and pile drivers to air conditioning units and photocopiers. Sounds with rhythm and tempo can exert influence through entrainment, which is the tendency of oscillating bodies to fall into synchrony, with the most powerful oscillators establishing the tempo. The Dutch scientist Huygens was the first to notice that pendulum clocks hanging closer to one another always end up in synchrony, with pendulums swinging exactly together. This entrainment effect works on us humans too, as we’ll see shortly.
All the effects of sound tend to increase with its intensity. We measure sound in decibels (dB), which are logarithmic. This means that we perceive an increase of 10 dB as a doubling of the volume level – so 80 dB of noise is not double the intensity of 40 dB; it’s 16 times as loud!
Before we move on, let’s define noise as ‘unwanted sound’. This is inevitably a moving target because it’s personal: my music might be your noise, and vice versa. Nevertheless, we can all agree on some sounds being noise: the sounds of road traffic, aircraft, construction and heavy industry are not going to top anyone’s list of favourites.
I hope you’re starting to see how rich, complex and fascinating sound is. Now let’s investigate the 4 powerful ways in which it affects you every day of your life.
PHYSIOLOGICAL
The human body is 70 per cent water, which makes us rather good conductors of sound. It’s not surprising, then, that sound can powerfully affect us physiologically, changing our heart rate, breathing, hormone secretions and even our brain waves. All our bodily rhythms can be affected by sound.
An age-old example of this is the fight/flight reflex. Many thousands of years of sharing caves with bears or tigers sharpened this instinctual response to any sudden or unexplained sound, and it still operates in you today. You may know intellectually that a dropped plate or backfiring car is not actually a threat – but long before you’ve processed that thought or any visual input, your autonomic nervous system, using much more primitive parts of your brain and working far faster than your conscious cortex ever can, has already acted, releasing hormones that accelerate your heart rate and increase blood pressure and blood sugar levels so that you’re ready for vigorous activity. Any sudden, loud or unexplained sound will have this effect.
Your heart rate and breathing can both be entrained by any loud external rhythm. The typical resting human heart rate is between 50 and 80 beats per minute (bpm), so it’s no surprise that loud dance music at 140 bpm will tend to accelerate your heart, even if you don’t take that sound as a threat! Your breathing will tend to follow suit. The opposite effect pertains in a spa or a meditation session, where slow-paced, gentle sound is often used to slow your heart and your breathing, and create physiological calmness.
TIP: If you ever have problems sleeping, I suggest playing the sound of gentle surf with about 6-10 cycles per minute in your bedroom. This rhythm and tempo is very like the sound of the breathing of a sleeping person and will entrain your breathing and promote rest; also, we tend to associate this sound with being carefree and relaxed and with natural tranquility, so it works on many levels.
From the moment you wake (preferably to something much gentler than the traditional startling alarm clock bell or beep) to the moment you retire, sound plays a significant role in your physiology, affecting your heart, your breathing, your hormone secretions and even your brain waves.
PSYCHOLOGICAL
The second way sound affects us is by changing our feelings, moods and emotions.
The clearest example of this is music. Take a moment to think of your favourite song. I’m joining you by thinking of mine, which is River Man by Nick Drake. As your song plays in your mind and you listen with imaginary ears, you may notice a shift in your mood. Music is a very powerful conveyor of emotion, and most people know how to use it deliberately either to counteract a feeling they would rather not have, or to enhance one they are enjoying. The process may be intuitive, but it’s also complex because music involves many factors: tempo and rhythm; timbre and dynamics; melody and harmony; and for vocal music lyrics and singing style too. Some of these are cultural; for example, the melancholic association of minor keys is strong in the classic European and American tradition, but far weaker in the Middle East, where some very happy music uses the minor mode.
On top of this, like all sound, music works powerfully by association. These associations may be global, like those evinced by the first 2 notes of John Williams’s famous theme from the film Jaws (I bet you just imagined them and thought of a shark!); they may be local, like