The three sections of the human ear. Left to right: sound waves travel from the outer ear via the ear canal to the tympanic membrane (eardrum) where those waves are transformed into mechanical energy and amplified by the three bones in the middle ear. The last bone, the stapes, is attached to the inner ear or cochlea, which converts the mechanical energy into electrical impulses, which are carried along the cochlear or auditory nerve.
We speak to some of the leading experts in hearing loss to find out why it happens, how to prevent it, and what to do if your hearing fails.
If I asked you to name the single most important piece of music or audio kit you owned, you might mention your keyboard, your computer, your guitar, your modular synth or your favourite compressor or effect. And you’d be wrong.
By far the most critical piece of gear you possess is your hearing: without it, it is very hard to pursue a career in sound! Yet surprisingly, most musicians, producers, and engineers know hardly anything about how hearing works, how to protect this amazing piece of organic technology, and what to do if it malfunctions — that is, if you develop hearing loss. That’s a shame, not only because on a practical level you should understand how hearing works in order to do your job, but also because the auditory system — an intricate set of biological amplifiers, resonators, multiband compressors, feedback circuits and additional aural signal processors — is so fascinating.
The Mechanics Of Hearing
I asked one of the foremost experts on hearing in the UK, Dr Brian CJ Moore, Emeritus Professor of Auditory Perception at the University of Cambridge, to provide an introduction to the Rube Goldberg machine that is our auditory system.
Dr Brian CJ Moore, Emeritus Professor of Auditory Perception at the University of Cambridge.Hearing starts with sound waves that reach the pinna, the visible portion of the ear on the sides of our head, and travels down the ear canal. The ear canal acts as a natural amplifier that “introduces a broad resonance that boosts frequencies around 3kHz. This partly accounts for the fact that our sensitivity for detecting soft sounds is best around 3kHz,” said Dr Moore.
At the far end of the ear canal, the sound waves cause a thin membrane called the eardrum (or tympanum) to vibrate. Those vibrations are transmitted to the three bones of the middle ear — the smallest bones in the human body — which ensure the efficient transmission of mechanical energy to the inner ear, or cochlea.
The third bone in the middle ear, called the stapes, is attached via a thin membrane called the oval window to the cochlea, described by Dr Moore as “a coiled up bony structure that’s filled with fluid.” The motion of the stapes on the oval window causes waves in the fluid that correspond to the frequencies of the original sound waves.
“If we imagine [the cochlea] unrolled, it’s like a straight tube with a flexible ribbon called the basilar membrane running along its length. Each place on the basilar membrane is tuned and responds best to a particular frequency in a continuous gradation. The end closest to the stapes responds best to high frequencies around 17,000Hz. The other end responds best to low frequencies around 50Hz.” Arrayed on the basilar membrane are receptors called inner hair cells (so‑called simply because they have tiny hairs at their tips; the proper name is stereocilia) that convert the movement of the basilar membrane into electrical signals that are sent to the brain. In other words, the inner ear is laid out similar to a piano keyboard: different places on the basilar membrane respond to different frequencies, high to low.
But the basilar membrane is far more than a ‘passive mechanism’ that moves in response to the wave of fluid in the inner ear. If that’s all it did, we wouldn’t be able to discriminate frequencies very clearly to perceive sounds over a very wide dynamic range. “In a normal healthy ear,” Dr Moore notes, “there’s another mechanism that affects the vibration of the basilar membrane.” This ‘active mechanism’ consists of three rows of outer hair cells that sit on top of the basilar membrane and function much like an extremely smart and adaptive multiband compressor or automatic gain control.
As the basilar membrane moves, Dr Moore explains, the stereocilia of the outer hair cells “are bent sideways, which causes a flow of electric current through the hair cells. In response, they actually expand and contract, changing their length and feeding energy back into the movement of the basilar membrane.”
This positive feedback mechanism does three things: “First, it sharpens the tuning on the basilar membrane. The sort of response pattern that you get to, say, a single sine wave is much sharper when this active mechanism is working than when it’s not. This sharper response enhances our ability to separate the different frequencies in a complex sound, something called frequency selectivity.”
Secondly, “The active mechanism produced by the vibration of the outer hair cells amplifies the cochlea’s response [and] makes us very sensitive to soft sounds. For very weak sounds, it can provide up to 55dB of amplification.
“The third thing that the outer hair cells do,” Dr Moore continues, “is introduce a form of amplitude compression or automatic gain control into the vibration patterns on the basilar membrane. They apply a lot of gain for very weak sounds, but the gain reduces as the input sound level goes up. At high sound levels, they don’t produce any amplification at all. And they may even damp down the vibration a little bit for very high sound levels.”
In short, our auditory system is nonlinear; it compresses and limits the audio signal it receives. “It’s got this automatic gain control mechanism built into it,” said Dr Moore. “Engineers often think that linear is good and nonlinear is bad. But in the case of the ear, nonlinear is good because it’s allowing us to hear over a huge range of sound intensities.”
Next, the electrical signals from the basilar membrane travel through several processing centres in the brain stem and eventually reach the auditory cortex in the brain. And just as the brain has specialised neurons that detect visual shapes like vertical, horizontal and diagonal lines, the auditory cortex “has neurons that only respond to certain specific patterns of sound like a frequency glide in a particular direction, or a certain pattern of amplitude fluctuation.”
Losing It
Assuming perfectly healthy ears, we can discriminate small changes in sounds with exquisite precision over a wide range of frequencies and intensities. But our hearing system, especially the inner and outer hair cells, can easily be damaged and when it is, our ability to hear will be adversely affected in all sorts of ways. For example, for reasons that are still unknown, the tiny bones in the middle ear can become fused together, a condition called otosclerosis. While many middle‑ear hearing losses can be quite serious — leading to a significant perceived drop in overall sensitivity that can reach more than 30dB — they can often be fixed via surgery.
Not so when it comes to damage within the inner ear. These so‑called sensorineural hearing losses can be extremely serious and are, unfortunately, usually irreversible.
While both aging and genes can cause sensorineural hearing loss, both beyond our control, by far the most prevalent cause is something we can control: prolonged exposure to intense sound for an extended period of time. In a paper he wrote for the Journal of the Audio Engineering Society, Dr Moore starkly described some of the problems overexposure to loud sound, like listening to highly amplified music, can create.
Damage to our inner hair cells, Dr Moore wrote, will lead to “poorer auditory discrimination and may contribute to reduced sensitivity to the temporal fine structure of sounds and to poor pitch perception.” In other words, our ability to perceive timbral and pitch differences can be badly affected by inner hair cell damage.
Even more seriously, “Damage to the outer hair cells within the cochlea leads to a loss of sensitivity to weak sounds, loudness recruitment (a more rapid than normal growth of loudness with increasing sound level), and reduced frequency selectivity.” That is, damage to the outer hair cells makes it harder to hear soft sounds; distorts our perception of loudness and dynamic range; and makes it more difficult to focus our hearing on specific frequencies and frequency ranges, such as those important for understanding speech.
This is a lot to absorb, but the point is this: you don’t want to damage your hearing by prolonged exposure to loud music. Ever.
You may be concerned about what you might learn from a hearing test. But if you’re a professional, get over it! If you don’t know the state of your hearing, you’ll be making decisions without a good idea of what you’re perceiving...
Racket Protection
But how can you protect your hearing? First, every expert I spoke to for this article recommended that all musicians, engineers, producers, etc, go to an audiologist and get their hearing tested regularly; at least once a year at minimum and more often if hearing issues arise. Try to find an audiologist that works regularly with others in music and audio. There are very good app‑based and online hearing tests available, but for more comprehensive testing, you should see an audiologist.
You may be concerned about what you might learn from a hearing test. But if you’re a professional, get over it! If you don’t know the state of your hearing, you’ll be making decisions without a good idea of what you’re perceiving (or not perceiving). In addition, there may be things you can do to help yourself hear better — and be better at your job — but you won’t know what they are.
The NIOSSLM sound level meter app for iOS. This app can be calibrated with an external microphone for highly accurate sound level readings. NIOSSLM provides an instantaneous read‑out of the sound level as well as a projection of how long it is safe to listen at a given level (the dose).Next, you should get a sense of how serious your risk is for sound‑induced hearing loss. Different organisations have somewhat different recommendations but an overall principle holds: the amount of time you can safely listen diminishes rapidly with increased volume levels.
One common rule of thumb is called the 3dB rule. For example, according to the National Institute for Occupational Safety and Health in the United States (NIOSH), it is safe to listen at a sustained level of 85dB(A) for up to eight hours, but if the sustained level rises a mere 3dB to 88dB(A), that halves to just four hours. And for every additional 3dB of level, the length of time available for safe exposure halves again: at 91dB(A), it is safe to listen for just two hours; and just one hour at 94dB(A). And yes, listening for just 30 minutes at 97dB(A) — which is common at live events or extended mixing sessions — risks developing serious and permanent sensorineural hearing loss.
One easy way to monitor your risk is via the NIOSSLM smartphone app (iOS only). This app provides you with both an instantaneous sound pressure level and an accumulated ‘dose’ level. Exceed the recommended daily dose and you’re at risk. It would be a good idea to keep this app active during extended mixing or mastering sessions, as we all lose track of time and listening levels have a habit of creeping up.
Plugging The Gap
When listening to or performing live amplified music, the first, and least expensive, way to protect your hearing is to purchase musicians’ earplugs. Dr Marshall Chasin, a Canadian audiologist who specialises in music‑related hearing health, recommends a highly effective yet inexpensive set of earplugs made by Etymotic Research called the ER20XS (about $20 £20 a pair). These reduce sound levels by 20dB across all frequencies, thus preserving the music’s tonal balance — something that the more ubiquitous foam earplugs you get in pharmacies can’t do. There are plenty of videos online that will instruct you on how to insert the earplugs properly to seal your ear canal.
Custom musicians’ earplugs with replaceable filters that provide different levels of attenuation.For a more personalised experience, you could step up to Etymotic’s ER15, which feature sound level filters at different strengths (‑9, ‑15 and ‑25 dB) and custom ear tips. To produce tips precisely moulded to your own ears (which many musicians find more comfortable than generic ear tips), you will need to visit an audiologist to get an impression of your ears.
Using IEMs Properly
For performing musicians, another important hearing protection system consists of good in‑ear monitors (IEMs). These can be used to replace traditional stage monitors (aka wedges) which are often turned up to hazardous levels due to the complexity of the auditory environment on stage.
To get a sense of how to use IEMs properly, I contacted Michael Santucci, AuD, a well‑known advocate for hearing health in the music industry. His company, Sensaphonics, manufactures high‑end IEMs like the 3DME Custom Tour System, which is equipped with a binaural mic array that enables musicians to hear their fellow band members on stage. The balance between the monitor mix and ambient sound is controlled via a smartphone app.
Sensaphonics’ 3DME in‑ear monitor system has an app that lets you mix the signal from a pair of binaural microphones into your monitor mix.
Dr Santucci — who has worked with many A‑list performers including the Dave Matthews Band and the Chicago Lyric Opera, and also runs a popular hearing clinic for musicians — notes that it is up to you to protect your hearing. “Nobody’s going to tell you to turn it down. Nobody’s going to tell you to protect yourself... it’s a voluntary thing.” And IEMs can help — if used properly.
When musicians wear IEMs in both ears, they can lose localisation and spatial cues and so are tempted to remove one. However, doing so is problematic because the exposed ear is then at high risk for hearing loss. Wearing both IEMs provides considerable benefit, taking advantage “of the binaural summation that results in a perceptual increase of 6dB over wearing only one”, says Dr Santucci.
Another plus: while wearing IEMs, many musicians find that they can play at a lower level than when using wedges — but they have to know they can turn them down. “From the start,” Dr Santucci recommends, “musicians should turn their IEMs down relative to what they’ve been used to from wedges.” And it is possible to turn IEMs down significantly more than wedges without affecting performance. Dr Santucci ran a study in which musicians were asked to turn down the volume of their monitoring system from their initially preferred volume to the minimally acceptable volume needed to perform. Performers using wedges could only lower the gain about 3dB, but IEM users could turn them down as much as 6dB and still perform comfortably.
Carrying On
But what happens if you develop hearing loss? Well, everyone’s capacity to hear is different, but many music and audio professionals with hearing loss have still been able to work. The Beatles’ producer Sir George Martin is one prime example. Sir George began to lose his hearing in the mid‑1970s but continued to produce numerous projects over the next 20‑plus years, including three solo albums for Paul McCartney.
In my own case, after developing severe otosclerosis in both ears, I wrote a large piece for orchestra and chorus called ‘Voices Of Light’ that became a Sony Classical bestseller and has been performed all over the world. Eleven years ago, my hearing got even worse when I lost the use of one ear, likely to a viral infection. Even so, I’m writing as much as ever, currently finishing an opera commission and starting an electric string quartet.
If you believe you are having hearing problems — if, say, you’ve noticed that you’re having trouble hearing higher frequencies or understanding speech — the first thing to do is to go to an audiologist and get a full hearing workup.
In the soundproof booth in the audiologist’s office, you will put on a pair of headphones and listen to a series of pure tones at different levels to determine their audibility threshold for you. The full range of hearing won’t be tested — typically, the test will only range from about 100Hz to 8kHz — but it is still useful for determining many hearing problems. Also, your speech comprehension will likely be assessed by listening to and then repeating a list of words or sentences. Additional tests will measure the response of your eardrum and other auditory functions. The results of all this testing will be displayed on an audiogram which superficially looks like (but is actually quite different from) a frequency response graph.
The author’s audiogram. Frequency is on the X axis, hearing level (a decibel scale) is on the Y axis. Normal hearing sits between 0 and 20 dB HL. This audiogram represents a moderate‑to‑severe loss of hearing.
Hearing Aids
After the testing, your audiologist will discuss the results with you. If you have a hearing loss, the audiologist may suggest hearing aids. While one hearing aid textbook drolly defined hearing aids as “basically a miniature public address system,” modern hearing aids are actually quite sophisticated. They typically include mic arrays that provide considerable directionality, digital converters with high sample and bit rates, and specialised signal processors that use multiband compressors and equalisers that your audiologist will adjust to help compensate for any hearing loss.
Many modern hearing aids have the ability to switch between different presets for help in different kinds of hearing situations — restaurants, outdoors or general hearing assistance — which are, understandably, biased towards optimising speech comprehension. But you can, and should, request a music listening preset which provides a somewhat flatter frequency response as well as less compression and less feedback suppression than the speech‑oriented programs.
In addition, many hearing aids also provide Bluetooth connectivity to smartphones, enabling you to stream audio and take phone calls. In my experience with multiple brands and models, the current quality of audio streaming to hearing aids is fine for podcasts, audiobooks and video calls, but for music streaming, the sound is somewhat compressed and thin. So, when I want to listen to music, I remove my hearing aids, put them somewhere safe, and use a good pair of earphones.
Hearing aids can be very helpful — and they’ve come a long way from Grandpa’s ugly body‑worn contraption with earpiece — but it’s important to understand that they can’t correct hearing in the way that glasses correct sight. My audiologist recommended that I wear my hearing aids all day (except when in the shower or swimming) in order to get used to the sound. At first the sound was very unnatural — I could hear pumping from the compressors and the sound was very aggressive — but after two weeks, I was used to it. I still had trouble hearing but the sound no longer called attention to itself.
Is there anything to do when performing or in the studio while wearing hearing aids? I asked a number of musicians and, of course, got a wide range of answers.
For live performance, musician Larry Revit, who is also a recording engineer and research audiologist, developed a personal sound system that employs strategically placed stage mics, signal processors, monitor mixes and an IEM equipped with binaural mics. This enabled him to tailor the sound to his hearing loss as well as hear his bandmates clearly. While it works quite well, Revit said, it is cumbersome; a wireless version would be more practical.
Whenever he rehearses and performs, Charles Mokotoff, a wonderful classical guitarist from Maryland, wears his hearing aids set to their music program, with the program’s settings tweaked via a smartphone app. When recording in his well‑equipped home studio, he listens to playbacks by attaching a special accessory made by his hearing‑aid manufacturer to the output jack of his studio’s audio interface. This enables him to stream the output from the interface directly to his hearing aids via a proprietary wireless protocol.
In my case, I’ve tried various techniques in my studio to try to hear better. Because I only hear properly from one ear (and then, only when wearing hearing aids), I’ve sometimes set up mono monitor mixes. I’ve also tried compensating for my hearing loss by brightening and limiting the monitor output. In truth, I’ve found such tricks less useful than one might expect them to be. When composing, I simply listen over very good speakers through my hearing aids. Whenever I use headphones, even if they’re an over‑the‑ears model, I take my hearing aids out and listen flat. Your own experience may be different, of course, and it pays to experiment. Just be sure always to keep the level of your monitor mix at a safe level!
There is one trick everyone I spoke to uses, including me: have someone whose ears you trust listen to what you’re doing. It is very easy to go down an aural rabbit hole without knowing it, even if you don’t have hearing loss, but especially if you do.
Last Word
Hearing, hearing protection and hearing loss are all vast subjects. But it is essential for all of us in the music and audio industries to know at least something about these topics and to be proactive about following up if problems arise.
In conclusion, I’ll just reiterate how important it is to understand and protect your hearing. It is by far your most valuable asset. So have fun, and enjoy your music‑making — and do so in a responsible manner that will help ensure you’ll be able to make music for many years to come.