1. An apparatus for generating a stereo side signal comprising a first side channel and a second side channel from a stereo input signal comprising a first input channel and a second input channel, comprising: a modification information generator for generating modification information, the modification information generator comprising a spectral weights generator for generating the modification information by generating a first spectral weighting factor based on a mono mid signal and on a mono side signal of the stereo input signal, and a signal manipulator being adapted to manipulate the first input channel based on the modification information to acquire the first side channel and being adapted to manipulate the second input channel based on the modification information to acquire the second side channel.