Ambience extraction and synthesis from stereo signals for multi-channel audio up-mix

In this paper we propose a frequency-domain technique to identify and extract the ambience information in stereo audio signals. The method is based on the computation of an inter-channel coherence index and a non-linear mapping function that allow us to determine time-frequency regions that consist mostly of ambience components in the two-channel signal. Ambience signals are then synthesized and used to feed the surround channels of a multichannel playback system. Simulation results demonstrate the effectiveness of the technique in extracting ambience information and up-mix tests on real audio reveal the various advantages and disadvantages of the system compared to previous up-mix strategies.