The Structure and Function of Hearing
Having healthy ears is of enormous consequence to music technologists and audio engineers. If an engineer or a technologist has unhealthy ears, then he or she will produce worse sounding music than an otherwise equally-qualified person with healthy ears.
Many people who are not music technologists or audio engineers routinely ignore the health of their ears by subjecting themselves daily to punishing sound pressure levels. The following behaviors are particularly problematic: listening to car stereos at high volume, attending rock concerts without earplugs, and using headphones on full blast.
These activities, if done repeatedly over an extended period, will cause irreversible hearing damage. From my point of view, losing one’s hearing by recklessly listening at high volume is analogous to losing one’s sight by recklessly staring at the sun.
The difference, of course, is that listening at high volume does not hurt the same way that staring at the sun does. Nevertheless, ear-destroying sounds do exist—especially in the realm of music technology. The working environment for the music technologist is daily bombarded with obscene sound pressure levels from amplifiers, speakers, drum sets, and many other ear-splitting sources.
Anyone who runs live sound or produces recorded music will tell you that ear protection is a necessary part of the job. Because of the dangers inherent to the activity of listening, it is important to understand some of the details about the sense of hearing.
This lecture focuses on some of those details by exploring the physiology of the ear, discussing further the problem of hearing loss, and introducing the methods of active listening.
The Anatomy of the Ear
The ear is the organ for hearing and equilibrium. It is divided into three parts: the outer ear, the middle ear, and the inner ear.
The exterior portion of the ear is called the pinna or auricle, and the corridor that leads from the pinna into the skull cavity is called the ear canal. The primary purpose of the pinna and ear canal is to collect sound and focus it into the middle ear.
The middle ear begins with the eardrum, which is a thin sheath of skin also known as the tympanic membrane. This membrane vibrates sympathetically with sound pressure waves, that is, the eardrum skin moves back and forth in concert with the compression and rarefaction of air molecules.
Affixed to the interior plane of the eardrum are three tiny bones positioned one after the other. They are known, collectively, as the ossicles. The purpose of these tiny bones is to amplify the vibrational energy of the eardrum.
The third and final ossicle (a very tiny bone known as the stapes) is affixed to the cochlea, which is a spiral-shaped cavity that contains fluid, several chambers, and a layer of tissue furnished with many thousands of hair cells.
The hair cells themselves possess further hair-like projections known as stereocilia. These stereocilia are what begin the transformation of sound energy into nerve activity.
Here is a picture of stereocilia taken by a microscope:
The sound energy transferred from the middle ear causes the fluid in the cochlea to wash over and perturb the hair cells and their attendant stereocilia. The sound energy is converted by the stereocilia into nerve impulses, sent to the brain via the auditory nerve, and experienced by the listener as sound.
The Nature of Hearing Loss
Sensorineural hearing loss, which is hearing loss caused by the degradation of hair cells within the cochlea, is due to prolonged exposure to high sound pressure levels.
The loss of hearing usually occurs slowly and over extended periods of time, so it is easy for one not to notice the degradation.
Prolonged exposure to loud sounds, or sudden exposure to very loud sounds (such as a gunshot or a jet engine), will damage hair cells or break them off completely.
When this happens, there is swelling and inflammation in the epithelium, which is the membrane within the cochlea that houses the hair cells. The broken hair cells and the inflamed cochlear tissue conspire to ruin your hearing.
Hearing loss occurs at specific frequencies and at specific amplitudes. For example, a person suffering from sensorineural hearing loss in the treble range may not be able to hear quiet whispers or children’s voices.
The body does not regenerate the hair cells in the cochlea, so losing them is like losing fingers. You cannot close your ears the same way that you can close your eyes, so there are only three ways to avoid damage to your body when you’re in a loud environment: (1) turn the sound down, (2) put earplugs in, or (3) leave the area.
The tell-tale sign that damage was done to your hearing is temporary threshold shift, which is a condition of desensitization that occurs to the ears in response to high sound pressure levels. Blood flow to the hair cells within the cochlea decreases when the body is exposed to extremely loud sounds, and this lack of blood flow is what causes this curious state.
Temporary threshold shift, also known as auditory fatigue, is often accompanied by tinnitus, which is ringing in the ears. If exposure to high sound pressure levels continues, then both threshold shift and tinnitus may become permanent.
It’s a clever idea to carry earplugs with you everywhere you go. You should make it a habit to use them while on city streets, at restaurants, at concerts, at rehearsals, etc.
The book, Audio in Media, categorizes the relative dangers of various sound pressure levels produced by various sources as follows:
- Sounds of 1 to 30 dB-SPL are considered faint or very faint and result from insect noises at night, a furnished living room, or a quiet office recording studio.
- Moderate loudness, which includes sounds from 30 to 60 dB-SPL, result from the sound of an average office or from the average conversation.
- Loud sounds (60 to 80 dB-SPL) result from such things as acoustic guitars from one foot away or a busy city street.
- Very loud sounds include heavy truck traffic, babies crying, the subway, and a trombone from sixteen inches away.
- At 120 dB-SPL, hearing crosses over into the realm of feeling, and at 150 dB-SPL permanent damage is being done.
- Sounds that are deafening include jet engines, rockets, and being twelve inches below a cannon muzzle (Alten 6).
The Function of Hearing
Sound is a never-ending torrent that unfolds over time, stimulates experiences in consciousness, and passes away without a trace. It’s truly a remarkable phenomenon. To understand it fully requires active listening.
To listen actively is to pay attention, moment to moment, to every detail of every sound before it evaporates.
There are two kinds of active listening done by audio engineers: analytical listening and critical listening. Each technique has a purpose for music production (Alten 278-279).
Analytical listening is paying attention to the form and content of sound. To listen in this way means to define all that you hear: those are birds, that’s an orchestra, those are Fender guitars, that’s an old recording, those singers are experts, and so on.
To listen analytically also means to answer questions like the following: What instrument is that? Is the guitar sound coming from an amplifier or from a PA system? Is the singer out of tune? When was that recording made, in the 1950s? Does this microphone of mine work best for drum overheads or should I borrow one from my friend?
It is the duty of the audio engineer to listen analytically. If he or she is hooking up sound equipment, running cables, and operating a mixing console, then he or she must be defining every sound encountered.
Every song heard while listening analytically will induce an inner dialogue of this sort: “This band I’m listening to consists of two guitars, a bass guitar, and a drum set; the singer is a woman, an alto; this recording was made in the modern era using digital equipment; it sounds like the bass player is using a short-scale instrument.”
For most sound engineers, the process of analysis, like the one just detailed, happens automatically. If you are to become a sound engineer yourself, then listening to music must cease to be a passive affair.
The other technique of listening is critical listening. Listening critically is to offer perspective and judgment upon that which you are listening. In other words, critical listening is listening for the purpose of constructing opinions.
This mental exercise demands a reference to what qualifies as objectively good. Attempting to make judgments about sound means having some criteria or prior reference of objectively good audio, and it means understanding what the merits and faults are of any given sound or music. Using commercially-produced audio as a reference is a good place to start.
Asking questions about the sound is another effective way to begin. Here are some sample questions: What is crucial to the quality of this musical performance? Should the singer be louder in the mix? Would this song sound better if it were ten beats per minute faster? Does having the whole band inside the control room make a net contribution to the quality of the mix?
For a music project, the person most responsible for critical listening is the producer. These specialized musicians are there to make judgments and dictate a course of action. A producer is a kind of project manager, and they are usually the final arbiter of any important decision.
Famous producers include George Martin (The Beatles), Quincy Jones (Michael Jackson), Dr, Dre (N.W.A.), Rick Rubin (Beastie Boys), and many others.
Critical listening as an intellectual exercise isn’t limited to producers. Many other musicians and audio technologists listen in this way. Composers and songwriters must focus on faults and defects in their music, too, or they can be sure their critics will do the work for them.
To create music without honest evaluation is to fail to listen critically, and failing to listen critically is a recipe for producing bad music.
Music technologists must keep their ears healthy and listen actively to make good music.
Practical steps for achieving these goals includes (1) buying and using earplugs, (2) asking questions about sound, and (3) apprising the essential elements of every song heard.
In order to become an adept music producer, you must be willing to devote yourself to sound and hearing.
Alten, Stanley R. Audio in Media 9th ed. Wadsworth, Cengage Learning: U.S.A, 2011.
“Cochlea.” The Free Encyclopedia. Wikimedia Foundation, Inc. 29 May 2016.
“Hair cell.” The Free Encyclopedia. Wikimedia Foundation, Inc. 29 May 2016.
“Organ of Corti.” The Free Encyclopedia. Wikimedia Foundation, Inc. 29 May 2016.
The Hearing Loss Association of America (HLAA). Types, Causes and Treatment. hearingloss.org. Web. 30 May. 2016.
Webster’s New World College Dictionary, Fourth Edition. Edited by Michael Agnes. IDG Books Worldwide, Inc. 2000.