10.1 Introduction

In the previous chapters, coding and rendering methods have been discussed for audio content that was in most cases produced for playback on a predetermined reproduction system, i.e. either stereo playback, a 5.1 home cinema setup, or alike. However, especially in the music domain, audio tracks have predominantly been produced for stereo playback. With the advent of multi-channel audio setups, many consumers would like to engage their full audio reproduction setup, even if the content was produced for two-channel stereophony. Therefore there is a demand for so-called upmix algorithms that convert conventional stereo material to a format for multi-channel playback, either using a standard 5.1 setup, or on more advanced reproduction systems (for example involving wavefield synthesis methods).

In this chapter, a technique is described to generate any number of independent audio channels, given two-channel stereo audio signals [85]. The technique is based on a perceptually motivated spatial decomposition for two-channel stereo audio signals, capturing the information of the virtual sound stage. The spatial decomposition allows to re-synthesize audio signals for playback over other sound systems than two-channel stereo. With the use of more front loudspeakers, the width of the virtual sound stage can be increased beyond ±30° and the sweet spot region is extended. Optionally, lateral independent sound components can be played back separately over loudspeakers on the sides of a listener to increase listener envelopment. It is also explained how the spatial decomposition can be used with surround sound and wavefield synthesis based audio systems.