Down-mixing using coherence suppression

A common problem in audio signal processing is to mix two or more signals into one sum signal. The mixing procedure, known as down-mixing, usually introduces some signal impairments, especially if two signals contain similar but phase shifted signal components. Summing up such signals results in severe comb-filter artifacts. In this paper, we propose a novel down-mix method which prevents comb-filter effects. This is achieved by suppressing the coherent signal parts of one input signal prior to mixing. During the down-mixing, a scaling gain is applied ensuring the preservation of overall signal energy. Furthermore, a phase-align extension to the down-mixer is introduced. The proposed down-mixer is evaluated qualitatively in comparison with two existing down-mix approaches as well as quantitatively by means of a distortion analysis.