an apparatus for providing at least first and second representations of an audio signal for use in a communications system is described . the apparatus comprises a first quantizer for quantizing at least a portion of the signal in accordance with a first multidimensional lattice to generate a first representation . the apparatus further comprises a second quantizer for quantizing at least a portion of the signal in accordance with a second , different multidimensional lattice to generate a second representation . in an illustrative embodiment , the first representation is a core representation containing core audio information . the second representation is an enhancement representation containing enhancement audio information . the core representation is necessary for recovering the audio signal with minimal acceptable quality . audio quality is enhanced when the core representation , together with the enhancement representation , is used to recover the audio signal . a method for use in such an apparatus is also described .