A decoding system reconstructs an n-channel audio signal on the basis of an input signal representing the audio signal, in different time frames, either by parametric coding or as n discretely coded channels. Parametric decoding uses a core signal and mixing parameters controlling a spatial synthesis stage, to which a downmix signal is supplied from a downmix stage. The downmix stage realizes a projection on the downmix signal based on an n-channel input signal, either a discretely coded signal or a core signal padded with neutral-valued channels. The padding may take place either on the decoding side (reduced parametric coding) or the encoding side. In an embodiment, an audio decoder (110) in the decoding system pads the core signal during an initial portion of each reduced parametrically coded time frame directly succeeding a discretely coded time frame and during a final portion of each reduced parametrically coded time frame directly preceding a discretely coded time frame.