Patent ID: 7602922

Claim:
A multi-channel encoder arranged to process input signals conveyed in N input channels to generate corresponding output signals conveyed in M output channels together with parametric data, wherein M and N are integers and N is greater than M, the encoder comprising: (a) a down-mixer for down-mixing the input signals to generate corresponding output signals; and (b) an analyzer for processing the input signals either during down-mixing or as a separate process, said analyzer being operable to generate said parametric data complementary to the output signals, said parametric data describing mutual differences between the N channels of input signals, so as to allow substantially for regenerating during decoding of one or more of the N channels of input signals from the M channels of output signals, said output signals being in a form compatible for reproduction in decoders providing for N or for fewer than N output channels to enable backwards compatibility, characterized in that the parametric data comprises at least one parameter describing a power of a central channel signal with respect to a power of a right channel signal and a left channel signal for a two channel downmix of the central channel signal, the right channel signal and the left channel signal, the at least one parameter being substantially given by: IID C = 10 ⁢ log ⁢ ⁢ 10 ⁢ ( ɛ 2 ⁢ ∑ k ⁢ C ⁡ [ k ] ⁢ C * ⁡ [ k ] ∑ k ⁢ ⁢ L ⁡ [ k ] ⁢ L * ⁡ [ k ] + ∑ k ⁢ ⁢ R ⁡ [ k ] ⁢ R * ⁡ [ k ] ) where C[k] denotes sample k of the central channel signal C; R[k] denotes sample k of the right signal R, L[k] denotes sample k of the left signal C and ε denotes a weight determining a strength of the central signal in the two channel downmix.