MP3 players have revolutionized the way we listen to music. These portable devices can store thousands of songs, providing an on-the-go soundtrack for our lives.

But as MP3 players become more popular, we're seeing more reported incidents of hearing loss caused by listening to excessively loud music. And increasingly, the aural damage is starting at a younger age. So we did a lot of research and talked to an audiologist. He helped us come up with some practical listening tactics so you can get the most out of your MP3 player while protecting your hearing — and all without compromising your listening experience.

How loud music leads to hearing loss

We've all been told repeatedly by parents and others that loud music damages our ears. And some of us believe that as long as our eardrums don't rupture, we're OK. But the real business of translating vibrations into what our brains understand as sound takes place behind the eardrum, in the inner ear. Read on for the straight story on how hearing loss happens.

Behind the eardrum is the inner ear. This is where the cochlea reacts to the vibrations transmitted by the tiny bones of the inner ear and converts them to signals that go directly to the brain.

Only the size of your pinkie's fingernail, the spiral-shaped cochlea is lined with over 30 thousand microscopic hairs. These extremely sensitive hairs are grouped in bundles, arranged in two rows, or bands.

The delicate hairs of the cochlea are where hearing damage from excessively loud volume levels occurs.

Each bundle detects a different pitch. The hair cells in the outer band, in addition to detecting sound, act as amplifiers to boost softer sounds to the inner hair cell band, which transmits the information to the brain.

Think of it as a piano keyboard wrapped up inside a snail shell. The highest pitched keys start at the opening, with the lower keys traveling on up into the recesses of the shell. The keys near the opening are exposed to the elements, so they're the most susceptible to damage.

At normal volume levels, the sensitive hairs in the cochlea wave back and forth, relaying information on to the brain. Excessively loud sounds hit these hair cells like a tidal wave crashing into a coastal forest — basically, hair cells break and their nerve connections get damaged. Extended exposure makes it worse. In fact, only three hours of too-loud headphone listening can be more harmful than exposure to the sound of an explosion at close range.

So what's the effect on hearing? Well, when a band of hair cells are damaged, the ear loses some of its ability to hear that particular frequency. Further exposure increases this loss. Also, once you lose a significant number of outer hair cells, hearing soft sounds of any pitch becomes very difficult as well. In some cases, the volume required to hear anything at all may be so loud that it in turn causes further damage.

The good news

This type of hearing loss from noise exposure — known as acoustic trauma — is usually preventable. You can safeguard your hearing by making a few simple changes in how you use your MP3 player — without sacrificing the enjoyment and impact of your music.

The simplest solution is to keep the volume of your MP3 player turned down. While virtually all players come with a printed warning about listening at dangerous levels, some — such as the Apple iPod® and Creative ZEN players — help you do something about it by including a volume limiter.

A limiter lets you lower the maximum volume level of your player so you can't accidentally boost it too high. This can also be a great help for parents to ensure their children listen at safe levels.

For the iPod, just go into the "Settings" menu on the player. Select "Volume Limit" and adjust the volume to what you want the allowable maximum to be. When you're done, you'll be prompted to enter a combination code to lock in the change.

Sony portable players use a similar system, with the exception of the combination code. The Sony Automatic Volume Limiter System (AVLS) lets you disable the limiter on the fly, and turn it back on in the same fashion. Creative players also let you turn the limiter on and off without a pass code.

A good rule of thumb when setting levels is to aim somewhere between one-half and two-thirds maximum volume. Remember that volume levels can vary from recording to recording, and some musical genres have a more tightly compressed — and therefore louder — sound. When setting levels, make sure you use a song that has the same volume as most of your music.

If you're thinking, "I won't be able to hear my music clearly if I turn the volume down more," then read on. We've also got ideas to help you get crisper music at lower volume levels.

There's a trade-off between file size and sound quality. Stuffing your MP3 player full of as many songs as possible can give you thousands of tunes to listen to, but at a cost. When you import a CD track, your music software program converts it to a sound file of a particular resolution, usually measured in kilobytes per second (Kbps). The lower the resolution, the smaller the resulting file — and the more detail lost.

Music with little detail tends to sound muddy. Most of us intuitively turn up such music in an effort to hear the missing details, and expose our ears to dangerously high volume levels in the process.

The software programs most MP3 players use, such as Apple's iTunes® or Windows Media Player 11, have default settings that determine what kind of file incoming music is converted to, and at what resolution.

Songs ripped from CDs are usually compressed to 128 kilobytes per second (Kbps) MP3 files. In the process of compressing the file, much of the audio information is discarded, leaving a general outline of the song. Much of the sonic detail that gives the music its character can either disappear or sound duller as a result.

This chart shows the relative file sizes of the same three-minute song saved in different formats, starting with the original CD track on the left. The smaller the file, the more sonic information is lost.

Switching the import default setting to a higher resolution, or using a different kind of file such as lossless compression format like FLAC, addresses that issue. A 192 kbps MP3 file can approach the sound of the original CD, although there's still some information lost in the compression. A lossless format, however, compresses the file and retains the original information. With a lossless track, you'll hear the original depth and detail of the music.

Generally, a lossless file is about ten times bigger than a 128 kbps low-resolution MP3 file of the same song. This means you can fit fewer lossless files on your player than low-res MP3, but there's a plus: you'll have significantly better-sounding music that can pack a greater punch at a lower — and safer — volume level.

Changing the default import setting on your music manager program is usually pretty simple. In iTunes®, for example, just go to "Preferences" and select "Import Settings." Follow the simple instructions to select a higher bit rate. For Windows Media Player, go to "Options" and select the "Rip Music" tab. You'll see a pull-down menu with your import format options.