AAC - MPEG-2 Advanced Audio Coding File

What is a AAC file

AAC files were designed with the intention of replacing MP3’s. The lossy compression provides better audio quality at similar bit rates. AAC files are standardized by the ISO/IEC as part of the MPEG-2 and MPEG-4 families though it was first introduced into the MPEG-2 Part 7 family. AAC files contain more sample frequencies than MP3’s, as well as up to 48 channels, higher efficiency of coding and filter banks, and higher coding accuracy for transient signals. Much like MP3 files, AAC files remove audio at frequencies the human ear cannot process to create smaller and more manageable files. The file size is significantly smaller with AAC files compared to MP3 files.

The MPEG-2 part 7 is defined with three profiles: Low Complexity (AAC-LC), Main profile (AAC Main), and Scalable Sampling Rate profile (AAC-SSR). AAC files allows temporal noise shaping, a non-uniform quantizer, and reworking of bitstream format (for 16 stereo channels, 16 mono channels, 16 low-frequency channels, and 16 commentary channels in a single bitstream). In 1999, the MPEG-2 part 7 was included in the MPEG-4 Part 3. This added Audio Object Types and Perceptual Noise Substitution. The current AAC standard is specified in ISO/IEC standard 14496-3. Audio masking is used in the lossy compression of the audio to discard of unneeded data while retaining quality.

Here's a small, but not exhaustive list of programs that can open AAC documents:

  • Windows Media Player
  • iTunes
  • KMPlayer
  • RealPlayer
  • VideoLAN VLC Media Player