A method for encoding N input audio signals, N>1, comprising the steps of: (a) converting each of the N input audio signals into a plurality of spectral components in a frequency domain; (b) for each of one or more, but not all, of the spectral components, downmixing the spectral components corresponding to the N input audio signals to generate a downmixed spectral component, leaving one or more of the spectral components for each of the N input audio signals unmixed; and (c) generating (212, 214, 112) an encoded audio bitstream based on the one or more downmixed spectral components and one or more unmixed spectral components, wherein step (c) comprises the steps of: replicating each downmixed spectral component to generate a plurality of replicated downmixed spectral components; converting the plurality of replicated downmixed spectral components and the one or more unmixed spectral components into N hybrid audio signals in a time domain; and applying an audio coding algorithm to the N hybrid audio signals to generate the encoded audio bitstream CHARACTERISED IN THAT: the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies dynamically over time; OR the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies as a function of bit rate. (a) converting each of the N input audio signals into a plurality of spectral components in a frequency domain; (b) for each of one or more, but not all, of the spectral components, downmixing the spectral components corresponding to the N input audio signals to generate a downmixed spectral component, leaving one or more of the spectral components for each of the N input audio signals unmixed; and (c) generating (212, 214, 112) an encoded audio bitstream based on the one or more downmixed spectral components and one or more unmixed spectral components, wherein step (c) comprises the steps of: replicating each downmixed spectral component to generate a plurality of replicated downmixed spectral components; converting the plurality of replicated downmixed spectral components and the one or more unmixed spectral components into N hybrid audio signals in a time domain; and applying an audio coding algorithm to the N hybrid audio signals to generate the encoded audio bitstream CHARACTERISED IN THAT: the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies dynamically over time; OR the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies as a function of bit rate. replicating each downmixed spectral component to generate a plurality of replicated downmixed spectral components; converting the plurality of replicated downmixed spectral components and the one or more unmixed spectral components into N hybrid audio signals in a time domain; and applying an audio coding algorithm to the N hybrid audio signals to generate the encoded audio bitstream CHARACTERISED IN THAT: the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies dynamically over time; OR the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies as a function of bit rate. the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies dynamically over time; OR the one or more downmixed spectral components have frequencies above a specified threshold frequency, and the one or more unmixed spectral components have frequencies below the specified threshold frequency, wherein the specified threshold frequency varies as a function of bit rate.