An input audio signal comprises a plurality of input audio channels. A KLT-based pre-processor transforms the plurality of input audio channels into a plurality of eigenchannels and provides metadata associated with the plurality of eigenchannels. Each eigenchannel is associated with an eigenvalue and an eigenvector. The metadata allows reconstructing the plurality of input audio channels on the basis of the plurality of eigenchannels. A selector selects a subset of the plurality of eigenvectors corresponding to a plurality of selected eigenchannels on the basis of a geometric mean of the eigenvalues. An eigenchannel encoder encodes the plurality of selected eigenchannels. A metadata encoder encodes the metadata.