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One Pair of Ears per Life

They are the best of tools, they are the worst of tools

We only get one pair of ears per life. They are complex organs that pick up vibrations in the air. Tiny hairs within the ear vibrate and these vibrations are converted into signals the brain understands as sound.

They can hear anything with a frequency between 20 and 20000 Hertz so its said. They can comfortably handle 120 DB TO 130 DB of dynamic range and the dynamic range of 16-bit audio is only 96 DB.

Although there are only two of them, our brains can interpret the tiny intervals between a sound's arrival at each ear to enable us to hear in surround sound.

If you were a salesman selling ears, these are the facts that you would trumpet loudly and proudly, but there's a lot of small print.

As you age, your hearing worsens and this process can neither be prevented nor reversed. Though research indicates this deterioration is less in women than men, no-one is exempt. The process is already well underway for everyone old enough to take this course.

Children under ten are able to hear some bat calls but after ten this ability disappears very quickly. There are devices called mosquitos, which shopkeepers can mount over their shop fronts to disperse crowds of loitering teenagers? How? By emitting a sound so high-pitched that almost no-one else can hear them, everyone else's hearing is already too degraded. As you've probably already guessed from these examples, this hearing loss generally effects high frequency content first.

I can't hear a 20 KHz sine wave, is my audio career at an end? Hopefully not because mine would be too. The fact is that this statistic that turns up everywhere is very optimistic. Not only does ones auditory frequency response vary with age, but also, for any given age, with gender. Again, the ladies really are the fairer sex when it comes to the upper limit of their hearing, even before age-related hearing loss sets in. The upper limit for men is about 17 or 18 KHz on average, depending on whom you ask.

Even if the tiny hairs that vibrate in our ears are all still intact, other things may inhibit our hearing. Ear-wax is the most common.

Before you test your hearing, you should be sure that your ears are reasonably free of wax. It's amazing how much better you can hear things once they are clear. Before discussing ways to clear your ears of wax, the following disclaimer is very important.

The information given below is not intended as medical advice and you should consult a medical professional if you are suffering any problems with your ears or anything else for that matter.

Most people use a Q-tip to clean their ears. The trouble is that this can cause damage and, more importantly, the purpose of ear-wax is to keep foreign bodies from damaging or infecting your ear. The more you put things in your ears, the more likely it is that ear-wax production will increase.

there are a number of medically approved and alternative treatments to remove wax from your ears. None of them is risk or side-effect free as far as we are aware and students should conduct their own research, mindful of the pitfalls of information found on the internet and consulting health professionals, before they decide upon which treatment they wish to embark.

Take Care of Your Ears

Wax build-up in the ears, inner ear infections and the like are temporary, other forms of hearing loss, such as most forms of noise-induced hearing loss are not. When you are subjected to sounds that are too loud, the hairs in your ear start to break. Once they've gone they don't grow back. Always listen to music at safe levels. If around noisy equipment or fireworks or guns, use ear protection, likewise when at a gig.

What Level is Safe

Volume is measured in Decibels. For every 6 DB increase, the amplitude of a sound doubles, the pressure the vibrating air exerts on the hairs in our ears doubles.

The average conversation is around 60 DB, city traffic is around 80. It is said that we can be exposed to up to 8 hours of sound at 85 DB, some say 80, without suffering hearing damage. The safe exposure time halves for every 3-5 DB increase above that, depending on the caution of the person you ask. Bearing in mind that rock concerts are around 120 DB and fireworks can be as loud as 150, you can see how dangerous they are to the life expectancy of your hearing.

The thing about noise-induced hearing loss is that it is cumulative. You lose a little at a time so that you don't notice it until it's far too late.

Use Ear Protection

Ear protection comes in two forms - ear-plugs and ear-muffs. Obviously they vary in quality. You can get ones that are tailor fitted to your ear canal but even ones from the drug store will offer a reasonable degree of protection. Bear in mind that cheaper brands of ear protection may not attenuate all frequencies equally. If you ware really good ear-plugs and ear-muffs or ear defenders together, you can achieve as much as -54 DB of attenuation, which is a significant degree of protection.

While not being medically trained in any way, we cannot recommend the responsible use of ear protection strongly enough. When you go out to gigs, firework displays and the like, please consider it!

More quirks and Limitations of the Ear

So, assuming you're young, responsible and your ears are free of wax, we then come to an interesting design quirk of the ear, which is that its frequency response is far from uniform, even for the best of ears. Listen to this series of tones and whooshes and try to determine which is loudest. They range between 50 and 10000 Hz, so should fall within the range of most people's hearing and the frequency response of most reasonable headphones. They also vary in length.

Hearing Tones

Although some of the sounds faded up and down at their tops and tails for a fraction of a second, all the sounds, bar one, reached the same maximum volume. I'm sure that some of the tones sounded much louder than others.

This is partly because our ears are most sensitive around the 3-4 KHz range and their sensitivity drops off rapidly, the closer you get to the ends of the audible frequency spectrum. To hear frequencies at the very extremity of human hearing, they actually have to be increased in volume until they near the pain threshold.

Exploiting the Quirk

If you play a piece of music very quietly, the same principal as discussed above becomes evident. It is easy to hear the middle frequencies, those that carry the tune, rather than the treble and bass, (the lowest and highest frequencies), where the bass guitar/sub-bass synthesizer lives at the bottom, and where the vocalists s sounds and the high-hats, tambourines etc live at the top. Mixing engineers can use this fact to their advantage.

If you turn down the middle frequencies using equalization and turn the bass and treble up for an element in a song you are mixing for example, you will make it sound louder to your listener.

Conversely, if you turn the bass and treble down and keep the mids for that same element, you will make it seem quieter and also further away, more distant, because the air absorbs high frequencies and the extreme low end more quickly than middle frequencies.

Timing is Everything

Loudness is a subjective term as we have seen, but it depends not only on the frequencies we hear, but also on the duration of the sound. Sounds that only last for a few milliseconds seem quieter than the same sounds if they last longer. this is a concept called temporal summation. Also we perceive the world in terms of its average sound level and are not good at determining peak levels.

The loudest sound in the series of noises you heard was the shortest burst of noise. It was almost four times louder than all the others, though, even if you did guess that it was louder, it is doubtful whether the difference seemed as great as it was.

Exploiting the Quirk

If you have a snare drum for example, you can make it sound louder by turning up its tail, i.e. the bit after the initial hit. This will put its volume closer to that of the initial hit, which is called the attack or the transient. We have made the average level of this sound greater and therefore, even though the transient is the loudest part and its level has not changed, the sound will be louder to us.

In fact, this is the principal that has enabled record producers to make music sound louder and louder over the years. There isn't any room left for them to increase the peak level of the audio, so they increase the average level instead by reducing the difference between that peak level and the lowest level. In other words the average level is increased at the expense of the dynamic range. It's about louder for longer rather than louder over-all.

Masking and mono-compatibility

The biggest problem mixing engineers face is masking. Masking happens when one sound is louder than another or when sounds occupy similar frequency ranges. It is difficult to separate one from the other. Think of how it feels when lots of people are speaking at once or how you can't really hear the esses of someone talking to you with the shower running.

When mixing engineers are dealing with the elements that make up a production, be they music or a film etc, they must worry about not only fundamental frequencies masking one another, but also the harmonics of one sound masking those of another, which can still cause blurring.

Masking could be mitigated by stereo separation, i.e. panning one instrument off to the left and the other off to the right. The trouble with this approach is that most listeners hear things in mono, either because their equipment only has one speaker or because they are not ideally placed in the stereo field created by a pair of speakers. Therefore all the elements of a mix must, in as far as possible, stand out from one another.

this means a mixing engineer must use equalization to remove unnecessary frequencies from a sound or boost the important ones. He/she must decide which instruments will have the greatest prominence, while other instruments must take a back seat. Listening to your work in mono, and on different equipment that may color the sound in different ways, is vital to achieving the best listening experience for as many people as possible.

The Haas Effect

Our ears have yet another limitation that mixing engineers can exploit. We have seen that we are not very good at perceiving sounds with very short durations accurately. We are not very good at perceiving tiny intervals between sounds at all. For this reason, sounds can mask other sounds that occurred just before them. there is a psychoacoustic trick that we can use to exploit this quirk as well though.

Helmut Haas discovered that if you make two copies of a sound, pan one copy hard right and the other hard left and shift one copy forward in time by no more than 35 milliseconds, we cannot perceive the gap between the sounds as an echo or delay. Instead, the result sounds like one sound that occupies the whole stereo field. this is used for synth pads, guitar solos and all sorts of other instruments. It is a good way to give a mono sound source more interesting stereo imaging.

Different delay settings sound slightly different depending on the nature of the sounds and you have to be careful. Making the interval between the two copies of the sound too short can result in phasing problems, where the sound will seem as though it is behind or above you. Also, the question of mono-compatibility rears its ugly head again. Unless you have the delay settings just right, collapsing this effect to mono may yield unpleasant comb filtering effects.

For a more in-depth discussion of the effects of phase including comb filtering, check out this .

Critical Listening

We have covered a lot of the ear's limitations in this article. Knowing about them and being able to listen for evidence of them in a mix will work to your advantage, not only in terms of being able to spot problems, but also in terms of the ability to take your mix to the next level by performing these sonic magic tricks to enhance your productions.

There is a difference between hearing, listening and critical listening. Critical listening is a skill that involves breaking audio down into its components, identifying problems and areas that could be improved or enhanced. Even those with poor hearing can, to a large extent, master this skill. Someone with average hearing but great critical listening skills is arguably of more value than someone with super-human hearing who doesn't know how to use it in an audio context.

Don't Give Up

Perhaps the warnings in this article regarding how to protect your ears have come too late. Perhaps years of rock concerts, a medical condition or some other factor have irrevocably damaged your hearing. Firstly, check with a doctor to see if anything can be done, but, if it can't, don't give up. Don't abandon your audio aspirations. Different branches of the huge field that is audio work make different demands on our ears. Perhaps you'll never be a mastering engineer, but you might still be a superb dialogue editor, sound designer or musician. If Beethoven can do it, who was deaf. Why not you. There is a whole branch of sound design dedicated to the production of LFE, low frequency effects. You could throw yourself into that. Fact is, if Jimmy Hendricks picked up the shoddiest guitar on the planet, provided it could be tuned and providing it had strings, he could still make it sound good. Up to a point, skill and an understanding of the limitations of what you're working with matter far more than the quality of the gear you have or the ears you have. you only get one pair of ears, protect what you have very carefully, but also, make the most of what you have!

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Page last modified on September 08, 2016, at 12:35 AM