32. A method as claimed in claim 29 wherein at least one additional element is added to each data encoding vector, wherein the added element(s) encode the overall power contained in spectral bands represented in the vector.
32. A method as claimed in claim 29 wherein at least one additional element is added to each data encoding vector, wherein the added element(s) encode the overall power contained in spectral bands represented in the vector. 33. A method as claimed in claim 32 wherein two elements are added to each data encoding vector to represent the overall power in spectral bands, these two elements arranged such that the sum of their squares is a constant across all input vectors that represent the spectrum of the input signal.