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.
