Why Can I Only Burn 80 Minutes of Music to a CD if My MP3s Take Up Less Than 700MB of Space?

When burning a CD, you can either burn it as a data disc or an audio CD. A data CD can hold up to 700 MB, while an audio CD can hold 80 minutes of sound. If you have 200 MB of MP3 files that add up to three hours of music, you can still only burn 80 minutes to the disc. Why is that?

What Happens When You Burn a Data CD

At the time of burning, you choose to burn either a data CD or audio CD. Your disc burning program burns the disc in a different format depending on the option you choose.

Data CDs are simple to understand. When you burn a data CD containing MP3s or any other type of file, your computer creates a disc containing those files. The files on the disc are the same size as they are on your computer. So, if you have 200 MB of MP3s you want to burn to a 700 MB disc, you can place the MP3 files and up to 500 MB of other data files on the disc.

Why Burning an Audio CD is Different

Burning an audio CD is different. Audio CDs are not the same thing as data CDs, and they do not contain MP3 files.

An audio CD contains audio data in CDDA (Compact Disc Digital Audio) format. This is uncompressed audio data, and it requires a lot more space than MP3 files, AAC files, or any other type of compressed audio file. A minute of CDDA audio always takes up the same amount of space on the disc, which is why you can only burn a maximum number of minutes to a disc. Even if the songs  you’re burning are in MP3 format, they have to be converted to the larger CDDA format if you want the disc to work in a regular CD player.

It goes the other direction, too. Audio CDs you buy in stores can only have a maximum of about 80 minutes of sound, but if you rip an album to MP3 or AAC format, it will use less than 700 MB of storage space on your PC. In order to convert CDDA to MP3, your computer uses a “lossy” compression process, where some data is thrown out. Otherwise, your ripped music collection would take up an awful lot of space!

Burning MP3s to Audio CDs Isn’t Ideal

If you burn an MP3 to an audio CD, the MP3s will expand to take up the same amount of space as the original audio data. However, the resulting disc will have inferior audio quality when compared to the original audio CD.

When you rip music from a CD to an MP3 file or AAC file, you’re not getting all the original audio data. Some of the data is discarded to ensure the MP3s have a small file size. The resulting MP3 files won’t necessarily sound as good as the original disc. How good they’ll sound depends on the encoder you use and its bitrate settings. Your headphones and speakers are also a factor: It will be easier to tell the difference with higher-quality, more expensive headphones.

This is why audio geeks like lossless formats like FLAC, which provide some compression but keep all the original audio data. If you burn lossless files like FLAC to a disc, you’ll have an audio CD with sound quality good as the original.

When you burn lossy files like MP3s to an audio CD, the MP3s will be converted to CDDA audio, which takes up more space on disc. But all the audio data that was discarded when the MP3s were created can’t be restored.

Of course, if you’re already happily listening to the MP3 files, an audio CD you burn from those files won’t sound worse any worse than the MP3s. But it won’t necessarily sound as good as the original audio disc, either.

Some Disc Players Support MP3 CDs

There’s a compromise available, too. Some CD players can read both standard audio CDs and “MP3 CDs”.

An MP3 CD is exactly what it sounds like. Rather than converting the MP3 files to CDDA while burning an audio CD, you burn the MP3 files to a data CD. The disc player then reads the CD, loads the MP3 files, and plays them just like a computer would.

To find out if your disc player supports MP3 CDs, look for an “MP3” logo on it. You can also read its instruction manual or check its specifications, and you should see MP3 support listed if it has it.

To create an MP3 CD, you simply burn a data disc and fill it with up to 700 MB of audio files. You may want to organize the MP3s into folders so they’re easier to navigate through on your disc player. Some applications, like iTunes, have an “MP3 CD” option, but you can achieve the same thing by burning the MP3 files to a data disc with any disc-burning tool.

These CDs won’t work on any old CD player, so this isn’t the most compatible solution. But, if you use a CD player that supports MP3 CDs—maybe your car stereo does, for example—you can burn MP3 CDs instead of audio CDs to fit more music on a disc.

Image Credit: Wikimedia Commons, Flickr

Chris Hoffman is a technology writer and all-around computer geek. He's as at home using the Linux terminal as he is digging into the Windows registry. Connect with him on Google+.