The possibility of hidden and safe communication has been one of the people’s old goals and needs. Today two important research aspects, that is, cryptography and data hiding are responsible to achieve this goal. Based on different security goals, in data hiding methods several kinds of sensitive and important data are placed in larger part of digital data as host, in a way that recognition of original data or changing them is impossible by unauthorized people. Therefore audio data have been considered as a suitable and comprehensive host to conceal data and various data hiding methods are used for decompressed audio formats while favored multi media compressed formats such as MP3 have been spread to transfer data by Internet and saving them. If the algorithms connected to decompressed audio formats are changed to compressed audio formats, there will be some problems. As a result, it is necessary to use other methods for compressed audio formats. Regarding that compressing MP3 has become a favored compressed method and data hidding is supposed to follow this compressed method, it has been attempted to examine the whole existing methods to conceal the data in audio files of MP3.
