Etymotic Research's earphones just may be the first audio product I've reviewed that the user into his or her body. Sounds yucky, I know, but, hey, we're always banging on about intimacy, so here's your chance. Unlike the 'earbuds' familiarised by the Sony Walkman and the hellspawn it launched - culminating in those provided with now-omnipresent, omni-oppressive iPod - Etymotic's ER4-P MicroPro Earphone actually enters the ear canal. But that's their secret weapon.

Moreover, it's cause for a behavioural modification previously unknown in audio. You really do have to re-learn headphone usage for this. Although they look, ostensibly, like generic earbuds, only better made and with elongated endpieces, the Etymotics are closer to earplugs custom-made for F1 drivers. This is not surprising as Etymotic Research, Inc. also produces ear protectors; the name even means 'true to the ear.'

Common ground with motor racing ear plugs is what makes the ER4 range so effective: proper insertion results in a 20dB-41dB noise cut, depending on which cushions you use. This level of noise reduction is precisely what an F1 driver needs, with his head mere inches from a 700hp-1000hp engine. For us, it means incredible isolation, useful on long flights, for example, and an air-tight seal that enables the ER4-P and its variants to produce simply sensational bass.

They're not, by the way, the first high-end earbuds, as there have been models over, say, £100 before; Shure, for one, has a range of very serious in-the-ear models, while Stax's SR-001s have been around for years. The SR-001s are, in effect, earbuds with a linking headband, as they're so small compared to conventional headphones; however, they do not invade your canal to anything like the depth of the Etymotics (or the Shures), and therefore do not create the necessary seal.

Etymotics arrive as a kit reminiscent of home medical apparatus. Inside the paperback-book sized black plastic box are the ER4-Ps on a 5ft lead with 3.5mm stereo plug, protected in a shaped, foam insert. A 1/4in plus adaptor is provided as well, plus three pairs of the flanged eartips (one pair pre-mounted), five pairs of foam eartips which provide better isolation, a shirt clip, a travel pouch, four replacement filters and a special tool for this purpose.

Both the spare filters and shirt clip are not mere conceits nor accessories. The minuscule filters protect the drivers from earwax and they must be replaced when clogged, which is inevitable no matter how obsessive your hygiene. The shirt clip is mandatory because the ER4 suffers unbelievably from the microphony of the cable rubbing against your clothing (or your flesh if you listen naked). You hear a whacking great, thunderous scrape every time the cable is moved. Judicious use of the clip helps - though I don't recommend clipping it to bare flesh.

That's the only downside to the Etymotics, if you can get past the notion of sticking something in your ear. The instructions, however, are comprehensive, with safety in mind. One simple test, too, helps to determine if you've inserted them with equal care: play a mono recording and the sound should be dead-centre. Unless you have one damaged ear.

The P suffix version is optimised for portables, with higher sensitivity at the frequency extremes, while the ER-4S is the more purist version without bass enhancement. (There's also an ER4-B optimised for binaural recording enthusiasts, for use with recordings not equalized for speaker playback.) Users of the ER4-P can buy an adaptor - a short cable with socket on one end and plug on the other - that converts the ER4-P to ER4-S for critical listening with home audio components.

Having the P-version without adaptor didn't stop me from trying the Etymotics with domestic audio gear; I'll report later on the differences between ER4-P and ER4-S after I get hold of the adaptor. For this review, I used the Etymotics with the Sony Walkman Pro, a couple of Panasonic and Sony personal CD players, and most critically with my own recordings made on the World's Greatest Portable: Nagra's ARES-BB. I also ran the ER4-Ps off the headphone socket from the Marantz PM-4 integrated, and used it extensively with HeadRoom's superb Total BitHead portable headphone amplifier.

No way am I going to minimise the trauma of using these for the first time. While I do firmly believe the adage 'Never stick anything in your ear larger than your elbow,' and, conversely, have total faith in the folks at HeadRoom, who supplied the review pair, it is disconcerting at best sliding the Etymotics into your ear-hole. I recommend following the instructions closely, including a pre-insertion ear cleaning. (See sidebar, 'Cleanliness Is Next To...')

As one who has a pile of super headphones to hand, along with countless earbud types, and as one who uses headphones at least two-to-three hours a day, I like to think that I have a handle on this direct-injection method of listening. No, I do not count thousands of hours of listening to personal hi-fis to be of similar worth, because most supplied-as-free earbuds suck, and the iPods' buds are legendary in their fragility and need for upgrading. Indeed, the Etymotics, along with the Shures, numerous Sennheisers, , are beneficiaries of the iPod headphones crappiness. But the Etymotics don't merely up the build quality factor. They sound so fantastic that they warrant the term 'reference' - and in the truest sense.

How much of it its simply the near-total isolation, how much is the driver, the cable the filter, I don't know. And while I await trying the ER4-S, because you can detect slight bass exaggeration when using these with domestic audio components. But for portable use, well, they're the ultimate upgrade. Whether using cassette, CD or purely digital, compressed downloads, the ER4-Ps exhibit a clarity that reminded me of Stax's full-blown models, in particular the Lambdas, with the smoothness of the best Grados.

Amusingly, I got as much joy from mono recordings as I did from stereo, because Etymotic hasn't solved the ultimate headphone dilemma, that of the sound being in your head instead of around and in front of it. (Will someone revive binaural in the digital era?) I still find the in-the-head-effect enough to make me prefer speakers every time, but the Etymotics are might seductive.

As for my stalwart Sennheiser 414s - which are certainly among the greatest headphones of all time - the ER4-Ps make them sound slightly veiled in comparison, with less impact. But there's a reason why manufacturers of conventional headphones needn't ever fear the Etymotics: they're not for everybody. Some will simply find them too creepy to use. The act of inserting them in the ear, having to clean off the wax periodically (sorry to seem coarse, but it's part of the Etymotic experience), the fiddly insertion technique - it's a world removed from the sheer comfort of the HD-414 or their newer, pocketable folding models.

If, on the other hand, their direct-injection intimacy appeals to you, the sense of isolation closing out all intrusion, you will never want to be without a pair, and you'll appreciate the underground buzz for the Etymotics. They're the closest thing so far to be directly wired to your sound source. Voices take on a realism that will have you turning your head, ripped from your reverie to see who entered the room. Transients are super-crisp, with no overhang, sibilance doesn't seem to exist, while retrieval of ultra-fine detail is without peer.

Even familiar material, like the remastered, two-disc version of Cream's , yielded surprise after surprise, so they'll help you to decipher mysteries, like mumblings on the Beatles with sublime efficacy. With Joss Stone's two CDs, the ER4-Ps let you hear the very textures in her voice that fooled listeners into think she's not a 17-year-old English lass. With Kodo drums, you hear bass not previously accessible via headphones. The sound of acoustic guitar on Antonio Forcione's CDs was conveyed with a wonderful woodiness and richness reminiscent of Sonus Faber Homage series speakers. But I kept going back to ancient mono recordings to hear Louis Prima, Johnny Ray. The Etymotics prised out details like an archaeologist with a dental probe.

You can acquire Etymotics from UK-based UAS Enterprises Ltd, via the web site at www.pjbox.co.uk or phone 01425 475563. Thanks to the weak dollar, UAS recently announced a reduction from £230 to £199. HeadRoom Corporation has wonderful package deals with their range of truly cool headphone amps; visit their site at www.headphone.com and see if you can make the hammered greenback work your way. Whatever method you choose, you can expect to reassess completely your approach to headphone listening. Especially if you're a putz with an iPod.