A decoder system for providing a stereo signal by complex prediction stereo coding, the decoder system comprising: an upmix stage (406, 407, 408, 409; 1433) adapted to generate the stereo signal based on first frequency-domain representations of a downmix signal and a residual signal, each of the first frequency-domain representations comprising first spectral components representing spectral content of the corresponding signal expressed in a first subspace of a multidimensional space, the decoder system being characterised by the upmix stage comprising: a module for computing a second frequency-domain representation of the downmix signal based on the first frequency-domain representation thereof, the second frequency-domain representation comprising second spectral components representing spectral content of the signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace, wherein the module is adapted to determine the second spectral components of the downmix signal by applying a Finite Impulse Response, FIR, filter to combine at least two of the first spectral components of the downmix signal; a weighted summer (406, 407) for computing a side signal on the basis of the first and second frequency-domain representations of the downmix signal, the first frequency-domain representation of the residual signal and a complex prediction coefficient (α) encoded in the bit stream signal; and a sum-and-difference stage for computing the stereo signal on the basis of the first frequency-domain representation of the downmix signal and the side signal; a first frequency-domain modifier stage (403; 1431) arranged upstream of the upmix stage and operable in an active mode, in which it processes a frequency-domain representation of at least one signal, and a passive mode, in which it acts as a pass-through; and a second frequency-domain modifier stage (410; 1435) arranged downstream of the upmix stage and operable in an active mode, in which it processes a frequency-domain representation of at least one signal, and a passive mode, in which it acts as a pass-through. an upmix stage (406, 407, 408, 409; 1433) adapted to generate the stereo signal based on first frequency-domain representations of a downmix signal and a residual signal, each of the first frequency-domain representations comprising first spectral components representing spectral content of the corresponding signal expressed in a first subspace of a multidimensional space, the decoder system being characterised by the upmix stage comprising: a module for computing a second frequency-domain representation of the downmix signal based on the first frequency-domain representation thereof, the second frequency-domain representation comprising second spectral components representing spectral content of the signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace, wherein the module is adapted to determine the second spectral components of the downmix signal by applying a Finite Impulse Response, FIR, filter to combine at least two of the first spectral components of the downmix signal; a weighted summer (406, 407) for computing a side signal on the basis of the first and second frequency-domain representations of the downmix signal, the first frequency-domain representation of the residual signal and a complex prediction coefficient (α) encoded in the bit stream signal; and a sum-and-difference stage for computing the stereo signal on the basis of the first frequency-domain representation of the downmix signal and the side signal; a module for computing a second frequency-domain representation of the downmix signal based on the first frequency-domain representation thereof, the second frequency-domain representation comprising second spectral components representing spectral content of the signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace, wherein the module is adapted to determine the second spectral components of the downmix signal by applying a Finite Impulse Response, FIR, filter to combine at least two of the first spectral components of the downmix signal; a weighted summer (406, 407) for computing a side signal on the basis of the first and second frequency-domain representations of the downmix signal, the first frequency-domain representation of the residual signal and a complex prediction coefficient (α) encoded in the bit stream signal; and a sum-and-difference stage for computing the stereo signal on the basis of the first frequency-domain representation of the downmix signal and the side signal; a first frequency-domain modifier stage (403; 1431) arranged upstream of the upmix stage and operable in an active mode, in which it processes a frequency-domain representation of at least one signal, and a passive mode, in which it acts as a pass-through; and a second frequency-domain modifier stage (410; 1435) arranged downstream of the upmix stage and operable in an active mode, in which it processes a frequency-domain representation of at least one signal, and a passive mode, in which it acts as a pass-through.