What is encoding?

Encoding is the process of changing the format digital audio is stored in. There are two broad types of encoding; compressed and uncompressed. Uncompressed audio is mainly found in the PCM format of audio CDs. For the most part, audio encoding means going from uncompressed PCM, to some kind of compressed audio format.

Compressed audio is split into two groups, lossless and lossy. Losslessly compressed audio can be decoded back into the exact uncompressed audio you started with. This is useful for archiving audio at the highest quality possible, and for people for whom storage space is not an issue. Lossy compression involves some loss of information hence the term "lossy".

Some common audio formats

Uncompressed            Compressed - Lossless      Compressed - Lossy
Audio CD                Apple Lossless Audio       Mp3
Audio DVD               TTA                        AAC
PCM WAV and AIFF        FLAC                       WMA
Record                  Monkey's Audio             Mini Disc (ATRAC)
Cassette                Shorten
DAT                     WavPack

Re-Encoding

A common question on the Serato forums is if transcoding (converting a file from one lossy format to another), or re-encoding into the same format with better settings will result in a better quality file. The answer is a resounding "NO". The artifacts from the initial lossy encoding will still be present, along with new (possibly far worse) ones. It is a good rule of thumb to only ever lossy encode from an uncompressed source.

An example of transcoding

Audio CD ➞ AAC ➞ MP3

In the above example, the transcoding step is from AAC to MP3. The quality of encoding will be greatly reduced in the final result. The preferred alternative would be to go back to the original CD:

Audio CD ➞ MP3

Useful audio encoding links

Wikipedia audio compression article
Ars Technica article on digital audio
Wikipedia sound recording and reproduction article