AAC file format
A proprietary format with lossy compression, which have been created as an alternative for MP3 with a higher quality of coding. Overtones out of human perception are being removed. AAC is two times less than MP3, which means 1/10 of CD digital data.
The format has been widely used since 1997 as the seventh release of the MPEG-2 family. As hardware players supply it, the format is highly demanded by music fans. It has been widely spread in Apple production and is being used by default in iTunes.
The format conception is similar to MP3, but it is more advanced. Being able to execute larger compression, it is represented as a separate segment of MPEG-4 standard used to create compact audio files. AAC is highly efficient with variable and continuous bitrate, with a sampling frequency of 8-96 kHz.
The current version complies with the standard of ISO/IEC 14496-3. Compression is performed based on an auditory masking effect that provides data reduction with no deterioration for sound quality.