Audio CDs - what format should I use to burn my Audio CDs?

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Summary: Audio CDs are different from data CDs. Typically your burning software needs to know how to create audio CDs, and you need to explicitly tell it to do so.

CDs you use on your computer, and CDs that you use in a standard CD player such as the one in your car are formatted quite differently. And while you can play those store-bought audio CDs in your computer, your computer's CDs are most likely not going to work in your car stereo or other audio CD player.

In a nutshell, the problem can be over-simplified this way: most car stereo players are not computers.

So what do you do?

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Let's look at the two different formats first.

Audio CDs are designed for one purpose, and one purpose only: audio. They contain raw, uncompressed data, in a very fixed format: 44,000 samples per second, with each sample consisting of a 16 bit (2 byte) number for each of the right and left channels.

If you do the math, that's 176,000 bytes per second, or 633,600,000 bytes for an entire hour of audio.

If you've ever seen blank CDs labeled as "70 minute" CDs, it's because they hold, roughly, 740 megabytes of data - enough for about 70 minutes of audio in that audio CD format.

Data CDs, on the other hand, hold anything. They're just another media on which you can store files from your computer. The format of a data CD is similar to the format of a computer hard disk - it has a file system, directories, folders and files.

And therein lies one difference: your car stereo knows nothing about file systems, files, folders and the like. All it knows is how to stream that raw audio data off of an audio format CD. Your computer, being a general purpose device, can do that too, of course, in addition to understanding the format of a data CD.

But there's a second difference.

Note that I said that an audio CD is "uncompressed". Every second takes up 176,000 bytes regardless of whether that's a second of symphony, a second of someone speaking, or a second of silence. MP3 is a compressed format - as is almost every other common audio format for internet downloads and computer use. It uses compression technology to make the file much smaller. A second of silence, for example, is going to require less data than a second of complex sounds. When you play an MP3 file, the software you use decompresses it as it's played.

Your car stereo probably doesn't have a clue about compression, or decompression, or MP3 or whatever else your computer's MP3 player just knows how to deal with.

So what do you do?

If you want to create an audio CD that will work in "plain" CD players, you'll need to use burning software that knows how to create one. I happen to use Roxio's Easy CD Creator, and it will, when burning, automatically decompress my MP3 files to the correct format as required by audio CDs. The trick is simply to select Roxio's "Music Disc Creator" program, and select "Audio CD" as the type of CD you want to create. Other CD burning software will have similar options or approaches.

The "catch", if you want to call it that, is that as I said, the audio CD is uncompressed. That means that while you might have been able to put 7 or 8 hours of MP3s onto a single data CD, you're out of luck: an audio CD will contain only about 70 minutes or so. It may take several audio CDs to hold what you might currently have on a single data CD.

The good news is that CD players are catching up. The ability to play MP3 files from data CDs is slowly appearing in car and home stereo CD players. In other words, like a computer, they'll be able to play both audio and data CDs. But unless that functionality is built in, it's not something that can be added later.

Personally, what I want is a "Line In" port on my car stereo so I can hook up my portable media player - any portable media player, not just the iPod - and listen to my music without ever having to have burned a CD at all. But that appears to be slow in coming.

Related:

• Ask Leo! - What does the 'X' in a 48X speed CD-ROM mean?

• Ask Leo! - Why doesn't music play smoothly on my machine?

• Ask Leo! - Can I ZIP my pictures or MP3 files to save space?

Article 10635 | Posted August 19, 2006