Editing Advanced Audio Coding (section)

===AAC's improvements over MP3===
Advanced Audio Coding is designed to be the successor of the ''[[MPEG-1 Audio Layer 3]]'', known as MP3 format, which was specified by [[ISO]]/[[IEC]] in 11172-3 ([[MPEG-1]] Audio) and 13818-3 ([[MPEG-2]] Audio).

Improvements include:
* more [[sample rate]]s (from 8 to 96 [[kHz]]) than MP3 (16 to 48&nbsp;kHz);
* up to 48 channels (MP3 supports up to two channels in MPEG-1 mode and up to [[5.1]] channels in MPEG-2 mode);
* arbitrary [[bit rate]]s and variable frame length. Standardized constant bit rate with bit reservoir;
* higher efficiency and simpler [[filter bank]]. AAC uses a pure [[MDCT]] (modified discrete cosine transform), rather than MP3's hybrid coding (which was part MDCT and part [[FFT]]);
* higher coding efficiency for [[Stationary process|stationary signals]] (AAC uses a blocksize of 1024 or 960 samples, allowing more efficient coding than MP3's 576 sample blocks);
* higher coding accuracy for [[Transient (acoustics)|transient signals]] (AAC uses a blocksize of 128 or 120 samples, allowing more accurate coding than MP3's 192 sample blocks);
* possibility to use [[Kaiser window|Kaiser-Bessel derived]] window function to eliminate [[spectral leakage]] at the expense of widening the main lobe;
* much better handling of audio frequencies above 16&nbsp;kHz;
* more flexible [[joint stereo]] (different methods can be used in different frequency ranges);
* additional modules (tools) added to increase compression efficiency: [[Noise shaping|TNS]], backwards prediction, perceptual noise substitution (PNS), etc. These modules can be combined to constitute different encoding profiles.

Overall, the AAC format allows developers more flexibility to design codecs than MP3 does, and corrects many of the design choices made in the original MPEG-1 audio specification. This increased flexibility often leads to more concurrent encoding strategies and, as a result, to more efficient compression. This is especially true at very low bit rates where the superior stereo coding, pure MDCT, and better transform window sizes leave MP3 unable to compete.