MPEG-2 AAC - Advanced Audio Coding

CD quality requires 96-128 kb/s

factor of 2 better than MPEG-1 Layer 2
factor of 1.4 better than MPEG-1 Layer 3

Non-Backwards Compatible (NBC)


Techniques - encoder/decoder

  1. Filter bank and block(window) switching: MDCT
  2. Temporal Noise Shaping: distributes quantization noise in time using prediction
  3. Prediction: uses LPC speech coding technique for appropriate signals
  4. Joint Coding: removes stereo redundancy M/S (L+R/S-D), or R/L joint intensity
  5. Scalefactors: shared gain value for a band of spectral coefficients to shape noise (49 bands for long window)
  6. Quantization: finer control of coef. quantization resolution (4/3 power)
  7. Noiseless Coding: huffman coding removes redundancy in banded and sectioned quantized spectrum (11 codebooks)
MP3'Tech - Mpeg2-AAC
MPEG-2 AAC Intro (Fraunhofer)
MPEG-2 AAC FAQ (Fraunhofer)
Result of AAC subjective tests (zip'ed word file)
MPEG-4 Reference Software (includes AAC)
MP3'Tech (MPEG source codes include AAC)

Major contributors

Ongoing encoder development by AT&T and FhG

NoBell Home - gjm - last update 02/12/1999