Parametric Coding for Spatial Audio

Abstract: This thesis presents a stereo coding technique used as an extension for the Enhanced Voice Services (EVS) codec [10] [8]. EVS is an audio codec recently standardized by the 3rd Generation Partnership Project (3GPP) for compressing mono signals at chosen rates from 7.2 to 128 kbit/s (for xed bit rate) and around 5.9 kbit/s (for variable bit rate). The main goal of the thesis is to present the architecture of a parametric stereo codec and how the stereo extension of EVS may be built. Parametric stereo coding relies on the transmission of a downmixed signal, sum of left and right channels, and the necessary audible cues to synthesize back the stereo image from it at the decoding end. The codec has been implemented in MATLAB with use of the existing EVS codec. An important part of the thesis is dedicated to the description of the implementation of a robust downmixing technique. The remaining parts present the parametric coding architecture that has been adapted and used to develop the EVS stereo extension at 24.4 and 32 kbit/s and other open researches that have been conducted for more specic situations such as spatial coding for stereo or binaural applications. Whereas the downmixing algorithm quality has been confronted to subjective testing and proven to be more ecient than any other existing techniques, the stereo extension has been tested less extensively. Yet the quality reached with the proposed reconstruction algorithms tends to highlight the potential of the codec that could be revealed by future work.