Advanced Audio Coding

Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. It was designed to be the successor of the MP3 format and generally achieves higher sound quality than MP3 at the same bit rate.^[4]

AAC has been standardized by ISO and IEC as part of the MPEG-2 and MPEG-4 specifications.^[5][6] Part of AAC, HE-AAC ("AAC+"), is part of MPEG-4 Audio and is adopted into digital radio standards DAB+ and Digital Radio Mondiale, and mobile television standards DVB-H and ATSC-M/H.

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.^[7] 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.^[4]

AAC is the default or standard audio format for iPhone, iPod, iPad, Nintendo DSi, Nintendo 3DS, Apple Music,^[a] iTunes, DivX Plus Web Player, PlayStation 4 and various Nokia Series 40 phones. It is supported on a wide range of devices and software such as PlayStation Vita, Wii, digital audio players like Sony Walkman or SanDisk Clip, Android and BlackBerry devices, various in-dash car audio systems,^{[when?][vague]} and is also one of the audio formats used on the Spotify web player.^[8]

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