Some of us probably remember “the old days”, when there were vinyl “LPs” (records), and cassette players. Many of us made “road tapes” – personal compilations of our favorite songs, to take in the car or on a Walkman. This concept hasn’t changed, although the lexicon is now filled with words like “Rip”, “Mix” and “Burn”.

First, a little about digital data. Digital media, in its raw, pristine state, takes up a lot of space on a computer. For example, the digital music files on a commercial CD weigh in at about 10 MB of data for every minute of song length. Digital video is even bulkier – about 250 MB per minute of video. In order to store more data in a smaller space, like a portable music player, or enable data to be streamed over the internet, technology called “compression” was developed. The basic idea is to use the speed of modern computers to make the file size smaller while retaining as much quality as possible. Compression is nothing new on computers – we create Zip and Stuffit files to compress text and images. As far as music goes, the industry audio compression standard is called MP3. MP3 is really shorthand for MPEG-3. MPEG is the acronym for Moving Pictures Experts Group, a consortium of media producers who establish standards in the industry. Microsoft has also introduced the Window Media Audio format (WMA). Without getting into the details of each format, let’s go back to our “road tape” scenario and see how they work. For simplicity, we’ll talk about MP3 files.

When you convert a song from a CD into MP3 format, your computer is actually using modeled characteristics of the human ear to compress the file. It removes some sounds, and therefore data, that the recording process captures, that we can’t even hear. It also removes “redundant” sounds – if two sounds occur at the same time, and one is softer (which we don’t hear), compression may remove that sound to make the file smaller. Basically, with all the techniques combined, that 10 MB of data for every minute of song becomes 1 MB of data.

When the MP3 player on your computer plays one of these files, it “decompresses” the file on the fly as it plays, providing you near CD quality audio.

After you create MP3 files for all the songs you want on your “road tape” and order them as you want, it’s time to “burn” them onto a CD. You guessed it – your CD burning program takes that MP3 file, and expands it, using the same human ear model, and converts it back into a format that any commercial CD player can read and play. Many commercial CD players now also have the capability to play MP3 files, decompressing them like the MP3 player on your computer.

You can also adjust the settings in your software, based on your storage capabilities, to create MP3 files at different resolutions, referred to a “bit rates”. MP3 files encoded for transfer over the internet are often done at a 128 Kbps bit rate. If you’re encoding MP3 files for storage on you computer’s hard drive, you might consider encoding at 192 Kbps or higher. Larger files, but higher quality.

As with anything digital, new formats are always on the horizon. Both MPEG-4 and Windows Media Audio format hold the promise of higher fidelity and smaller files sizes. MP3 players with 40 GB capacity are coming. At 3 MB per song, that’s (if my math is right) over 13000 songs in a box the size of a deck of cards – more than enough to get you across country and back a couple of times on your road trip.

© 2003 Peter F. Zimowski