Low Complexity Decoding in Parametric Stereo Audio Coding Scheme

ABSTRACT

The Parametric Stereo (PS) audio coding is an audio coding object of High Efficiency Advanced Audio Coding version 2 (HE-AAC v2) which was standardized by ISO/MPEG in 2004. Traditional audio codec, e.g. MP3 or AAC, utilize “Psycoaustic Model” and “Masking Effect” to achieve high compression efficiency. However, they mainly process the signal with single channel. Different from traditional audio codec, the PS audio coding incorporates the characteristics of two channels, to extract spatial parameters and to down-mixes stereo signals into a mono signal. The PS can save almost half data size which provides great help in storage and transmission.

Nevertheless, the complexity of PS decoder is nearly twice larger than that of PS encoder, which causes a serious problem in implementing PS on portable devices. Therefore, this thesis proposes a modified PS coding scheme to reduce the complexity of decoder. The encoder extracts and transmits the additional residual parameters from the residual signal and the mono signal. On the contrary, the decoder reconstructs the residual signal by the mono signal and the transmitted residual parameters. In addition, we detect the existence of transient signal and measure the artifact of reconstructed residual signal. Finally, “Energy compensated algorithm” is proposed to reduce the artifact produced by the transient signal.

The proposed scheme can improve the Objective Difference Grade (ODG) of audio quality measurement “EAQUAL” with 0.6 score. Combining with audio coder AAC, the modified PS coding scheme still maintains a good performance at low coding bitrates.