"THE TAPE was so compressed it would have hacksawed your ears off," complained a visiting drummer in the One Two office the other day, spectacularly slagging a demo he'd been asked to listen to.

Hacksaw your ears off, actually, and there'd be a much more serious effect than mere loss of hearing. So what is it that the ears do? Why are they there? How do we hear? In many ways, you see, hearing is a secondary function of the ears. They'd opt for the balancing act given half a chance.

There are these fluids in the ears which enhance your awareness of your head's relative movement and your particular relationship to gravity. In other words, they tell you which way up you are.

This is all of little consequence to us musical types. Falling over's easy. What about hearing?

Fortunately, ears are very effective transducers, connecting vibrations in the outside air to nerve impulses for the brain. So effective that if you were to compare the ears' efficiency to that of the eyes, then the minimum energy detectable by the ear would be equivalent to the eyes picking out a 50W bulb 3000 miles away. Just don't ask how they worked that one out.

That funny shaped bit of skin and cartilage you see on the outside of the bonce is only the beginning of the story. It's intended to direct those sound vibrations toward the little hole. As you'll no doubt have noted, that part of the ear is not at all symmetrical, thus giving no preference to any incoming frequency.

The head-located flap, called the pinna, is intended to direct and locate the incoming sounds, not amplify them. The hole extends some 4cm into the skull, is about 8mm in diameter, and is lined with skin that secretes ear wax and has lots of thick hairs to stop earwigs and other insects getting in.

Down the end is the ear drum, a bit like parchment stretched across the gap between outer and middle ear. Three minute bones form a chain between the ear drum and inner ear, across the chamber of the middle ear, transmitting the detected vibrations.

Now swallow. Go on, swallow. Hear a little clicking noise? That's the Eustachian tube opening, and a handy little thing it is, equalising the air pressures either side of the ear drum for efficient transmission of those vibrations. If you've got a cold or you travel on a wild pilot's plane, you get funny squeaking noises and hearing impairment as the pressures sort themselves out along the Eustachian. In the inner ear is the main hearing gadget, the cochlea (Greek = snail, which is what it looks like, ear dwellers tell me).

The thing to bear in mind if you're fascinated by such goings-on deep in your skull is that these are tiny, tiny bones and membranes. Even if you were to bung your ear up against Terry's 4x12 going full pelt, your ear drum would only move its full distance, which is in the region of the diameter of a hydrogen atom, .000000001mm (measure it).

Stepping back from the 4x12, you will now feel a deadness in the ears. This is due to the muscles around your tiny, tiny eardrum tensing as the huge sound walloped in, getting very quickly tired, and saying words to the effect of, "Sorry mate, we're going on strike for a bit." Impaired hearing, says the ear doc, or otologist as they like to call themselves, but only for a little while. Later on you'll get a little ringing in the ears. This too has a flash name, tinnitus.

It can hang about for a long time, however, this tinnitus. For years and years in extreme cases, and manifest itself as much more than ringing. One otologist's patient described her raging tinnitus as "the first three bars of 'God Save The Queen' endlessly repeated". The Sex Pistols sampled, no less.

But in good form, what can the ear pick up, given the lamp-3000-miles-away nonsense above? Traditionally, the figure quoted is 20Hz to 20kHz — ie from well below the low E on the bass guitar to well above the pingy zing coming from the cymbals. But of course it varies from person to person (and roughly one in 2000 of us is deaf anyway). Piano tuners have got so fed up with our lack of sensitivity in the lower frequencies that they often leave the lowest notes on the piano alone — not worth the bother.

But a wonderful mathematical theory allows us to hear sounds well out of these frequency ranges. Supposing the flash herbert with the DX7 finds very, very high frequency sounds, and bungs a 25k and 30k signal towards your ear oles. What they'd "detect" (rather than actually hear) is a difference-tone of 5k — in other words the "difference" between 25 and 30. Some foreign violinist called Tartini discovered these in the eighteenth century. When he played, say, a G (384Hz) and a B (480Hz), he clearly heard a third tone (which was the difference-tone, 96Hz, two octaves below the G he played). Being foreign, he called them "terzi suoni".

Be thankful you have two active ears to take all this stuff in. Stereo (first demonstrated in 1881 on two telephones) relies on two ears, you know. Naturally, a directional sound source will enter one ear fractionally earlier than the other, giving the brain a big clue. Take an owl, for example. What pretty feathers. And one of its ears is positioned slightly more forward than the other, see? So it can locate the precise direction a sound is coming from to within one degree. Poor old humans can only manage a three degree tolerance. We try to emulate owls by cocking our heads to one side. Just watch the engineer's subtle head movements when s/he's listening to a mix.

Supposing only one ear's working, though. Brian Wilson managed some gems with only his left ear fully functional, so don't worry too much. In fact, theory has it that the right ear is more efficient at processing speech sounds, the left ear better at music — which helps explain Mr Wilson's survival of monauralism. And which leads to my theory that Japanese people hear with the other side of the brain to us westerners... but I see the end of the page beckoning.

One last bit of advice: walls have ears. The influential American composer Aaron Copland underlines this warning. "The most unforgettable sound of all," he noted, "was that of a massed orchestra and band of some one thousand high school performers in an Atlantic City convention hall all simultaneously searching for the note A. It is hopeless to attempt to describe that sound. Jericho's walls must have heard some such unearthly musical noise."