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mp3 encoding The creation of mp3 files from any other audio format, most commonly CD (slang: 'ripping' a CD).

The key advantage of an mp3 file over any other audio format is its small file size. However there is a trade off, as audio quality is lost in the process. This is known as lossy compression. Other examples of lossy compression include jpeg and mpeg. The opposite of this is lossless compression] which manages to reduce the file size without effecting the quality of the data in the file. An example of this compression is LZW, commonly used to compress tiff graphics files, and gif files, the most common web graphics format.

Hence, the primary decision to be made when encoding an mp3 is how much compression you want - the higher the compression, the worse the sound. If storage space and portability is no issue, (such as for use on your PC) then keep the files large is recommended. However, if space is limited, in a portable mp3 player for example, you may want to crunch the files down more, at the expense of the audio quality.

There are two types of compression variable bit rate and constant bit rate. This refers to the amount of data per second in for an mp3.
Variable bit rate varies this figure based on the compexity of the music, some sounds will compress easily and some not. Usually, your compresison software will allow you to set a quality level for your variable bit rate encoding, such as 'low' or 'medium'.
Constant bit rate implies that the amount of data per second is constant. This typically ranges from 16kbps to 320kbps. For use in a portable mp3 player, or for streaming over the web, 32kbps or 64kbps is a recommended starting point. For local PC use, 128kpbs or higher is best.

An mp3 file contains more than just audio data - it also contains information about the audio. This is typically the artist and song name, but can included album name, track position on the album (ie, track 3 of 9), and genre. This data is contained within the file's ID3 tag. When encoding the file, your encoding software will give you the option to include an ID3 tag, and ask you to pick a version. I would recommend version 2.3, which now seems resonably well supported by mps mp3 players.

One other important thing to remember: The legal status of encoding your own mp3s from CDs is qustionable. Whilst you are probably fine encoding your own CDs into mp3s for personal use, (rather like making audio casette recordings, back in the days...), distribution of these files is almost certainly illegal. This probably includes napster, in case you were wondering. Note: I am not a lawyer, so this is not legal advice, only conjecture.

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