A Stereo to Mono Dowmixing Scheme for MPEG-4 Parametric Stereo Encoder

In this paper, a signal-adaptive, stereo-to-mono downmixing scheme associated with MPEG-4 parametric stereo (PS) encoding is presented. The proposed scheme minimizes signal cancellation and coloration due to inter-channel phase misalignment. By using the inter-channel phase difference information which is calculated as a PS spatial parameter, the phase of the stereo signals are aligned. Subsequently, a simple averaging is carried out to mix the signals. The need to perform power equalization to preserve the overall power of the stereo signals in the downmix signal is eliminated. This leads to a significant saving of computational power. The scheme allows overall phase difference (OPD), one of the spatial parameter sent in PS bitstream, to be coded with minimum bit consumption. As a result, the entropy is reduced from 1.31 bits/symbol to 1 bit/symbol. This scheme is useful especially for stereo audio with a significant amount of side signal component