This led to the development of the modified discrete cosine transform (MDCT), proposed by J. Rao in 1973, publishing their results in 1974. The discrete cosine transform (DCT), a type of transform coding for lossy compression, was proposed by Nasir Ahmed in 1972, and developed by Ahmed with T. 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, and is also one of the audio formats used on the Spotify web player.

ĪAC is the default or standard audio format for iPhone, iPod, iPad, Nintendo DSi, Nintendo 3DS, YouTube Music, Apple Music, iTunes, DivX Plus Web Player, PlayStation 4 and various Nokia Series 40 phones. 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. Tests 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 320 kbit/s for 5.1 audio. 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). 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.ĪAC 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. ĪAC has been standardized by ISO and IEC as part of the MPEG-2 and MPEG-4 specifications. Designed to be the successor of the MP3 format, AAC generally achieves higher sound quality than MP3 encoders at the same bit rate.

MPEG-4 Part 14, 3GP and 3G2, ISO base media file format and Audio Data Interchange Format (ADIF)Īdvanced Audio Coding ( AAC) is an audio coding standard for lossy digital audio compression.

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