MP3 is the most common music (sound) file format. This format was developed by Fraunhofer IIS and Thomson. This format for storing and transmitting music (sound) files in digital form uses signal compression technology. That is why, unlike the previously widespread WAV format, MP3 files (full name - MPEG Audio Layer-3) are much smaller in size, and their sound quality is much higher. The MP3 format was one of the first and most successful sound compression methods. One of the important characteristics of this process is the degree of compression, that is, how much data is transferred per unit of time. Standard MP3 encoding is from 64 to 320 kb / s.
AU is an audio file format created in Audacity. This is a free cross-platform program designed to edit audio files. AU format (Audio Units) was developed by Sun Microsystems. This format greatly simplifies the task of reliable storage of audio files. An AU file consists of 3 parts: a header (max. 24 bytes), a description block of various sizes, and audio data. The file format is used on computers running the Sun or Unix operating system. However, it opens with other audio players. The AU format uses the logarithmic encoding method, previously very popular on computers running the Sun SPARCstation operating system. Previous sound file formats, in order to reduce the size, used the logarithmic scale of recording samples. Among the representatives of such formats, the Sun AU group of formats, which are still in action, gained great fame. Problems with opening the AU file usually manifest themselves when there are no corresponding applications that would be installed on the PC. Applications that use .AU files are Apple QuickTime Player, Microsoft Windows Media Player, Real Player, Winamp, and other widely used audio players. And this is the vast majority of professional audio editors.