MPEG AAC

Apart from quantization of transform coefficients, MPEG-4 Advanced Audio Coding technique [17,18] (schematic diagram below) features several additional coding tools that allow to achieve high compression: prediction of coefficients, temporal noise shaping and perceptual noise substitution.

The MPEG AAC coding technique (simplified)

Prediction in MPEG AAC exploits similarity of corresponding transform coefficients that is observed between consecutive frames (blocks of MDCT coefficients representing a block of time domain signal) if the signal is stationary. A bank of adaptive predictors is employed to predict the coefficients in current frame using coefficients from previously decoded frames (each coefficient has its own predictor). Transmitting only the prediction error which is usually small, requires less bits than transmitting full coefficients.