Setting the record straight on those digital music files

November 06, 2003|By Mike Himowitz

FROM TIME to time, I'm wrong. Usually, when I'm wrong in print, it involves an opinion, which is always open to argument and further refinement. But now and then, to my shame, I blow it on a fact.

Sometimes this gives me a chance to set things right and offer readers more information - hopefully all correct.

So here goes:

In last week's column about iTunes, Apple's online music store, I wrote that Apple sells music in a proprietary format called AAC. As a small legion of Mac fans wrote to protest, AAC is not proprietary but an industry standard. It just happens that Apple is the only online music company that uses it.

I regret the error - but the subject brings up a question I've been getting more frequently as online music stores proliferate: What's the difference between MP3, WMA, and now AAC files?

It's an issue that usually comes up when someone downloads music that his or her software or portable player can't handle.

The alphabet soup refers to abbreviations for different schemes that encode music into digital form and compress it for storage on a computer's hard drive or a handheld player.

The abbreviations often show up as three-letter extensions at the end of file names - the extension tells you what kind of file it is.

To play a tune, you'll need software or hardware designed to decode that type of file and turn it back into music.

Likewise, to create a music file from an audio CD or direct sound source, you'll need software that can compress the data and store it in the format you choose.

These coding-decoding schemes are known in the trade as codecs.

When Phillips and Sony developed the compact disc format in the late 1970s, they settled on a standard scheme for "sampling" the sounds musicians made and translating them into a series of binary ones and zeros.

The codec developed for audio CD players, still in use today, wasn't very efficient. It requires close to 10 megabytes of data to store a minute of music. Although a compact disc can store 74 minutes of music, the format still required too much data to move music around over the computer networks that developed in the 1980s and '90s.

So, an industry organization called the Moving Picture Experts Group (MPEG) developed a way to compress the amount of data a recording required through "perceptual noise shaping," a process that discards levels of sound that the ear can't perceive.

What does that mean?

Let's say you're at a concert with a rock band playing at jet engine-level volume. The person next to you whispers something. In a normal room, you can hear the whisper - but in the concert hall it's drowned out by those 20-foot-tall speakers. So, if you want to compress the sound of the concert, you can ignore the sound waves produced by the whisper.

That's a pretty simplistic description for the complex mathematical formulas behind the wildly popular MP3 format. It compresses music to about 1 megabyte per minute while maintaining near-CD audio quality.

As computers became more powerful and CD-ROM drives became common, programmers developed software to "rip" music from CD audio tracks and record them as compressed MP3 data files.

MP3s were small enough to be transmitted over the Internet, which led to the music file-sharing craze and a major headache for the recording industry. Virtually all music players can handle MP3 files.

Since Microsoft didn't own or control the MP3 standard - a state of affairs that Chairman Bill Gates can't abide - the company decided to develop its own compressed music format, known as Windows Media Audio, or WMA for short.

Microsoft claims WMA files produce better audio quality with less data than MP3s. This is a great issue for audiophiles to fight over.

Unlike the MP3 format, Microsoft's music scheme allows copy protection to be built into music files. That has made it the format of choice for legitimate online sellers such as MusicMatch and the revitalized Napster service.

Microsoft's Windows Media Player will play WMA files. So will some, but not all, portable music players. Media Player will play MP3s and"rip" audio CD tracks into WMA files, but not into MP3s unless you buy a third-party add-on program.

Got it so far?

The AAC format that Apple chose for its iTunes downloads stands for Advanced Audio Coding. It's an open standard developed by the same consortium that developed the original MP3 format. A major difference is that it allows recording companies to build in copy protection.

AAC backers claim it produces better sound with less data than MP3 or WMA encoders. That's another matter for audiophiles to argue over.

Apple is the only major online music distributor to license the AAC format. Its iTunes software is the only major program that can play copy-protected AAC files and its iPod player is the only current hardware produced by a major manufacturer that can handle AACs.

Apple's iTunes software and iPod can play MP3 files, too, but not Microsoft's WMA files.

Still with me?

The upshot of all this competition is that for the immediate future, purchasing music online from different sources will probably require different software for your PC (no problem - the companies give it away or your can buy it relatively cheaply).

If you want to take that music with you, you might need different portable players (a more serious problem - nobody gives those away).

If you're converting a CD collection to digital files on your PC, you're still best off sticking with the MP3 format. It might lack a bit of the quality of WMA and AAC, but you can play your music anywhere.

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