Balanced-delay filterbank for Closed-Loop Spatial Audio Coding

Closed-loop configuration has been introduced to Spatial Audio Coding (SAC) which make it possible to minimise distortion introduced during the quantisation and encoding processes. Significant performance improvement has been shown and reported in some papers. However, implementation of closed-loop system directly to MPEG Surround (MPS) is still problematic due to the unbalanced-delay filterbank that is used in the MPEG standard which is not appropriate for a closed-loop system that needs synchronisation between the original audio signals with the target audio signals. In this paper, we investigate the delay characteristic of the Quadrature Mirror Filterbank (QMF) which is used in several MPEG standards. Based on this study, a balanced-delay QMF is proposed and tested in a closed-loop MPS system. The results of the experiments show that approximately 8 dB of SNR improvement is achieved when applying balanced-delay filterbank compared to the unbalanced-delay filterbank as specified in MPS.