Low bit-rate high-resolution spectral envelope coding for audio encoder and decoder

DETAILED DESCRIPTION I claim: 1.
An encoder of one or more channels of input signals comprising signal samples, said encoder comprising splitband means for generating a subband signal block comprising a plurality of subband signals by applying a filter bank to said channels of input signals, each subband signal representing a respective frequency subband of said channels of input signals, scaling means for generating scaled representations of two or more subband signals, each of said scaled representations comprising a scaling factor associated with one or more scaled values, wherein said scaling means comprises means for adjusting the value of said scaling factor and said scaled values in a respective one of said scaled representations to restrict the magnitude of a difference between said scaling factor and a scaling factor in another or said scaled representations in accordance with frequency selectivity characteristics of said filter bank, differentiating means for generating differential coded representations of one or more of said scaling factors, and formatting means for generating an encoded signal comprising said scaled values and said differential coded representations.
2.
An encoder according to claim 1 wherein said filter bank is implemented by one or more discrete transforms.
3.
An encoder according to claim 1 wherein said filter bank is implemented by a bank of digital band-pass filters.
4.
An encoder according to claim 1 wherein each of said subband signals represents a respective frequency subband of a respective one of said channels of input signals.
5.
An encoder of two or more channels of input signals according to claim 1 wherein at least one of said subband signals represents a composite of a respective frequency subband of two or more of said channels of input signals.
6.
An encoder according to claim 1 wherein each scaling factor is associated with a single scaled value.
7.
An encoder according to claim 1 further comprising means for determining the information requirements of said encoded signal which results from the use of various coding modes, and then adaptively switching to the mode which achieves the greatest reduction in information requirements, said coding modes including various ranges to restrict said magnitude and various numbers of scaled values associated with a respective scale factor