MP3 (formally MPEG-1 Audio Layer-3 or MPEG-2 Audio Layer-3) is a digital format for storing audio files and audio streaming. MPEG programmers designed the format. It is one of the most required codecs for digital coding. The format is widely used in various file-sharing sites for evaluation downloading.

Due to lossy compression in this audio format, it is possible to compress CD tracks up to 1/10 of their original size while maintaining high playback quality. Moreover, it can be encoded at higher or lower bit rates to adjust the resulting quality. Overtones, which cannot be perceived by a human ear, are removed. Complex algorithms allow for a smaller size of tracks. As a result, one compact disk can contain several hundred songs. MP3 is compatible with all the most popular operating systems and is supported by most modern DVD-players and music systems.

Before MP3 introduction, MPEG-1 had been widely used. That format contained not only audio data but images as well. MP3 breaks an audio file into parts of the same length. When the processing is over, each part is packed into its frame. It involves the spectral limit technology that requires a continuous input signal to provide the use of two adjacent structures.

When spectral deleting is over, the file is to be compressed with mathematic methods. If necessary, the compression rate can be changed, even inside the same frame. Files of 128 kbit/s have 11-fold compression. Further reduction of the file size will lead to a significant deterioration in sound quality.