The invention relates to multi-channel audio signal processing, in particular to a method of processing a multi-channel audio signal and to a signal processing device. A method of processing a multi-channel audio signal is disclosed, comprising the steps of: receiving an input sum signal (s) representing a sum of a first audio signal and a second audio signal; receiving an input difference signal (d) representing a difference between the first and second audio signals; decorrelating the sum signal to provide a decorrelated sum signal (sd); calculating a first gain (gs) from a cross-correlation of the sum and difference signals (s,d) and the power of the sum signal; calculating a second gain (gsd) from a cross-correlation of the sum and difference signals (s,d) and the power of the sum and difference signals; calculating an output difference signal (d′) from a sum of the first gain (gs) applied to the sum signal (s) and the second gain (gsd) applied to the decorrelated sum signal (sd); and providing an output stereo audio signal (l,r) from a combination of the output difference signal (d′) and the input sum signal (s).