With digital music, there are several types of files.
- Lossy compressed files such as AAC or MP3 files. These use several techniques to make music files smaller, including psychoacoustic modeling (removing sounds you don’t hear), and standard file compression (shrinking parts of files when repeated strings of characters are found). When you compress a file to a lossy format, such as when you rip a CD, you lose some of the original sound data. (But not 90% of it, as Neil Young wants you to believe.)
- Lossless compressed files such as Apple Lossless or FLAC. These files retain all the original musical data while taking up much less space than the uncompressed files on CDs. Audio from a CD ripped in Apple Lossless format takes up about 250–400 MB, or around 7 MB per minute, depending on the type of music. When you play these files, they are uncompressed on the fly, and they become bit-perfect equivalents of the original CDs or uncompressed files.
- Uncompressed files are AIFF and WAV files, which encapsulate raw sound data from a music CD in file headers so the data can be used on computers. This uncompressed format takes up a lot of space, around 600–700 MB per disc, or about 10 MB per minute of audio.
I get a fair number of emails from people who think that they can convert their lossy (MP3 or AAC) files to a lossless format and have better quality files.
This is simply wrong. Once that data is lost, it’s gone. You can convert an MP3 or AAC file to an Apple Lossless or FLAC file, but it will be exactly the same quality as the original lossy file. The only way to create lossless files is to rip your CDs in a lossless format, or purchase downloads in Apple Lossless or FLAC formats.
So if you think you’re going to get better sound by converting your lossy files to lossless, you won’t. You’ll simply be wasting your time, and using more disk space to store the files.