An apparatus for decoding an encoded multichannel signal, comprises: a base channel decoder (700) for decoding an encoded base channel to obtain a decoded base channel; a decorrelation filter (800) for filtering at least a portion of the decoded base channel to obtain a filling signal; and a multichannel processor (900) for performing a multichannel processing using a spectral representation of the decoded base channel and a spectral representation of the filling signal, wherein the decorrelation filter (800) is a broad band filter and the multichannel processor (900) is configured to apply a narrow band processing to the spectral representation of the decoded base channel and the spectral representation of the filling signal.