Efficient transform coding of two-channel audio signals by means of complex-valued stereo prediction

Traditional MDCT-based perceptual audio coding schemes employ mid/side and intensity stereo techniques to allow efficient joint coding of the two channels of a stereophonic signal. These techniques, however, provide only little coding gain for critical stereo signals characterized by spectral components with a distinct level or phase difference between the channels. To overcome this deficiency, we propose an extension to the mid/side coding paradigm that utilizes complex-valued inter-channel linear prediction in the MDCT spectral domain. The required imaginary spectrum (MDST) is calculated in a computationally efficient manner without additional algorithmic delay. A formal listening test conducted in the course of the ISO/MPEG standardization of the unified speech and audio codec USAC illustrates that the proposed stereo prediction approach provides significant improvements in coding efficiency and shows that at 96kb/s, excellent quality can be obtained even for critical signals.

• Type: Journal
• Year: 2011
• Where: ICASSP
• Authors: Christian R. Helmrich, Pontus Carlsson, Sascha Disch, Bernd Edler, Johannes Hilpert, Matthias Neusinger, Heiko Purnhagen, Nikolaus Rettelbach, Julien Robilliard, Lars F. Villemoes
• Keywords: Efficient Joint Coding, ICASSP 2011, Little Coding Gain, Perceptual Audio Coding, Signal Processing