Optimized processing for reducing channels of a stereophonic audio signal

A non-transitory computer readable storage medium storing a computer program comprising instructions for executing a method for downmixing a stereophonic signal in order to obtain a monophonic signal, when the instructions are executed by at least one processor of a downmixing device, wherein the method comprises, for a current frame:

• a first step of selecting a downmixing operation from first and second procedures which use filtering of the stereophonic signal and rephasing of the signals, the selection being made according to a phase indicator, representative of a measure of a degree of phase opposition between the frequency components of channels of the stereophonic signal;
• and
• a second step of selecting between one of the first and second procedures, selected at the end of the first selection step, and a downmixing procedure without rephasing, the selection being made according to a value of an energy ratio between the channels of the stereophonic signal.