| 摘要 |
A method is described for packing variable-length entropy coded data 120 into a fixed rate data stream along with resolution enhancement data 130, the method providing tightly constrained propagation of transmission channel errors and graceful degradation of signal resolution as entropy-coded data rate increases. An application to a multiband ADPCM (Adaptive Predictive Pulse Code Modulation) audio codec is also described. Features described include maintaining a conveyor comprising a sequence of slots, A-H, including a start slot, H, and an end slot, A, wherein each slot is adapted to contain one or more bits and wherein the conveyor is adapted to effectively move the bit content of each slot to an adjacent slot after the passage of a time step, whereby bits are conveyed from earlier slots to later slots with the passage of each subsequent time step; and for each input signal/data/codeword: placing/distributing the bits of the input into slots of the conveyor; and retrieving a delayed/compactified codeword from the end slot. Further features described include: the input data being represented as a coarse codeword 120 and a touchup/fine codeword 130, wherein the coarse codeword in placed into slots in the conveyor and the touchup codeword is combined with the delayed output codeword to furnish a composite codeword 110; and input into the conveyor is placed into the first slot, and bits are moved (conditionally) from an earlier slot within the conveyor to a later slot having at least two fewer bits. Other disclosed embodiments include: decoding a sequence of composite codewords using a LIFO stack (e.g. Figure 10); encoding and/or decoding using coarse codewords and touchup codewords wherein bits from the coarse codeword are placed unconditionally into the formatted binary representation and a bit from the touchup codeword is placed conditionally into a predetermined touchup bit position; and quantising or inverse quantising a signal sample in dependence on whether a sign bit is forced (e.g. Figure 11). |
