Encoder comprising an inter-channel phase difference calculator device and method for operating such encoder

The invention provides an encoder for producing an audio bitstream from a stereo audio signal. The encoder comprises: a downmixer configured for downmixing the stereo audio signal in order to produce a mono audio signal; an inter-channel phase difference calculator device configured for calculating an inter-channel phase difference for each time segment of a plurality of consecutive time segments of the stereo audio signal; and a bitstream producer configured to produce the audio bitstream in such way that the mono audio signal and the inter-channel phase differences for the plurality of consecutive time segments are embedded in the audio bitstream; wherein the inter-channel phase difference calculator device comprises an inter-channel phase difference calculator being configured for calculating the inter-channel phase difference depending on a global inter-channel phase difference of a current time segment and depending on a mean bandwise inter-channel phase difference change of the current time segment.