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Advanced Audio Coding

Advanced Audio Coding
Filename extension.3gp, .aac, .m4a, .m4b, .m4p, .m4r, .mp4
Internet media type
audio/aac
audio/aacp
audio/3gpp
audio/3gpp2
audio/mp4
audio/mp4a-latm
audio/mpeg4-generic
Developed byAT&T Labs, Dolby Laboratories, Fraunhofer Society, Sony Corporation
Initial releaseDecember 1997 (1997-12)[1]
Latest release
ISO/IEC 14496-3:2019
December 2019 (2019-12)
Type of formatLossy audio
Contained byMPEG-4 Part 14, 3GP and 3G2, ISO base media file format and Audio Data Interchange Format (ADIF)
StandardISO/IEC 13818-7,
ISO/IEC 14496-3
Open format?Yes
Free format?No[2]

Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. It was developed by Dolby, AT&T, Fraunhofer and Sony,[3][4][5] originally as part of the MPEG-2 specification but later improved under MPEG-4.[6][7] AAC was designed to be the successor of the MP3 format (MPEG-2 Audio Layer III) and generally achieves higher sound quality than MP3 at the same bit rate.[8] AAC encoded audio files are typically packaged in an MP4 container most commonly using the filename extension .m4a.[9][10]

The basic profile of MPEG-4 AAC is commonly called AAC-LC (Low Complexity). It is widely supported in the industry and has been adopted as the default or standard audio format on products including Apple's iTunes Store, Nintendo's Wii,[11] DSi and 3DS and Sony's PlayStation 3.[12] It is also further supported on various other devices and software such as iPhone, iPod, PlayStation Portable and Vita, PlayStation 5, Android and older cell phones,[13] digital audio players like Sony Walkman and SanDisk Clip, media players such as VLC, Winamp and Windows Media Player, various in-dash car audio systems,[14] and is used on Spotify,[15] Apple Music,[a] and YouTube web streaming services.[16] AAC has been further extended into HE-AAC (High Efficiency, or AAC+), which improves efficiency over AAC-LC.[17] Another variant is AAC-LD (Low Delay).[18]

AAC supports inclusion of 48 full-bandwidth (up to 96 kHz) audio channels in one stream plus 16 low frequency effects (LFE, limited to 120 Hz) channels, up to 16 "coupling" or dialog channels, and up to 16 data streams. The quality for stereo is satisfactory to modest requirements at 96 kbit/s in joint stereo mode; however, hi-fi transparency demands data rates of at least 128 kbit/s (VBR). Tests[which?] of MPEG-4 audio have shown that AAC meets the requirements referred to as "transparent" for the ITU at 128 kbit/s for stereo, and 384 kbit/s for 5.1 audio.[19] AAC uses only a modified discrete cosine transform (MDCT) algorithm, giving it higher compression efficiency than MP3, which uses a hybrid coding algorithm that is part MDCT and part FFT.[8]

  1. ^ ISO (1997). "ISO/IEC 13818-7:1997, Information technology — Generic coding of moving pictures and associated audio information — Part 7: Advanced Audio Coding (AAC)". Archived from the original on 2012-09-25. Retrieved 2010-07-18.
  2. ^ Advanced Audio Coding (MPEG-4) (Full draft). Sustainability of Digital Formats. Washington, D.C.: Library of Congress. 22 June 2010. Retrieved 1 December 2021.
  3. ^ "AAC in the Chips". Stereophile.com. 2002-06-09. Retrieved 2025-04-11.
  4. ^ "Dolby Laboratories Announces AAC Support Program" (PDF). 2000.
  5. ^ "MP3's Competitors Line Up". Streaming Media Magazine. 2001-04-17. Retrieved 2025-04-11.
  6. ^ ISO (2006) ISO/IEC 13818-7:2006 – Information technology — Generic coding of moving pictures and associated audio information — Part 7: Advanced Audio Coding (AAC) Archived 2016-03-03 at the Wayback Machine, Retrieved on 2009-08-06
  7. ^ ISO (2006) ISO/IEC 14496-3:2005 – Information technology — Coding of audio-visual objects — Part 3: Audio Archived 2016-04-13 at the Wayback Machine, Retrieved on 2009-08-06
  8. ^ a b Brandenburg, Karlheinz (1999). "MP3 and AAC Explained" (PDF). Archived from the original (PDF) on 2017-02-13.
  9. ^ "Apple seeking coder to port iTunes to Windows". Archived from the original on 2024-09-08. Retrieved 2025-04-11.
  10. ^ says, James (2021-10-17). "MP3 vs. AAC (.m4a) with Allan Tépper – PES 120 – Podcast Engineering School". Retrieved 2025-04-11.
  11. ^ Caron, Frank (2007-11-14). "Wii Photo Channel update adds customization, removes MP3 playback". Ars Technica. Retrieved 2025-04-11.
  12. ^ "PS3™ | Importing audio CDs to the system storage". manuals.playstation.net. Retrieved 2025-04-11.
  13. ^ "Sony to support AAC -- heck not to freeze over". Engadget. 2006-05-10. Retrieved 2025-04-11.
  14. ^ "Pioneer Releases Car Audio Package for a Limited Time in the Overseas Markets to Commemorate the 80th Anniversary of its Foundation | News Releases | News and Events | About Us | Pioneer". Pioneer Corporation. Retrieved 2025-04-11.
  15. ^ "Audio file formats for Spotify". Spotify. Retrieved 20 September 2021.
  16. ^ updated, Joe Svetlik Contributions from Becky Scarrott last (2022-07-25). "MP3, AAC, WAV, FLAC: all the audio file formats explained". whathifi. Retrieved 2025-04-11.
  17. ^ "Dolby adds High-Efficiency AAC to MPEG 4 patent pool". 2004.
  18. ^ Rose, Matthias (2012-06-28). "Understanding MPEG Audio Codecs From mp3 To xHE-AAC". Electronic Design. Retrieved 2025-04-11.
  19. ^ "The AAC Audio Coding Family For Broadcast and Cable TV" (PDF). 2013. p. 6. Archived from the original (PDF) on 2023-09-28. Retrieved 2024-01-29.


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