A method and a device are described for processing a stereo signal obtained from an encoder, which encodes an N-channel audio signal into spatial parameters (P) and a stereo down-mix comprising first and second stereo signals (L0, R0). A first signal and a third signal are added in order to obtain a first output signal (Low), wherein the first signal (L0wL) comprises the first stereo signal (L0) modified by a first complex function (g1), and the third signal (L0wR) comprises the second stereo signal (R0) modified by a third complex function (g3). A second signal and a fourth signal are added to obtain a second output signal (R0w). The fourth signal (R0wR) comprises the second stereo signal (R0) modified by a fourth complex function (g4), and the second signal (R0wL) comprises the first stereo signal (L0) modified by a second complex function (g2). The complex functions (g1, g2, g3, g4) are functions of the spatial parameters (P) and are chosen to be such that an energy value of the difference (L0wL,R0wL) between the first signal and the second signal is larger than or equal to the energy value of the sum (L0wL+R0wL) of the first and the second signal, and the energy value of the difference (R0wR−L0wR) between the fourth signal and the third signal is larger than or equal to the energy value of the sum (R0wR+L0wR) of the fourth signal and the third signal.