Computationally efficient adaptive bit allocation for coding method and apparatus

#The invention relates in general to low bit-rate encoding and decoding of information such as audio information. More particularly, the invention relates to computationally efficient adaptive bit allocation and quantization of encoded information useful in high-quality low bit-rate coding systems.

#There is considerable interest among those in the fields of audio- and video-signal processing to minimize the amount of information required to represent a signal without perceptible loss in signal quality. By reducing information requirements, signals impose lower information capacity requirements upon communication channels and storage media.

#Analog signals which have been subject to audio compression or dynamic range reduction, for example, impose lower information capacity requirements than such signals without compression. Digital signals encoded with fewer binary bits impose lower information capacity requirements than coded signals using a greater number of bits to represent the signal. Of course, there are limits to the amount of reduction which can be realized without degrading the perceived signal quality. Much of the following discussion is directed more particularly to digital techniques, but it should be realized that corresponding considerations apply to analog techniques as well.

#FIG. 1 is a block diagram illustrating one embodiment of an encoder in an encoder/decoder system incorporating forward-adaptive allocation.

#FIG. 2 is a block diagram illustrating one embodiment of a decoder in an encoder/decoder system incorporating forward-adaptive allocation.

#FIG. 3 is a block diagram illustrating another embodiment of an encoder in an encoder/decoder system incorporating forward-adaptive allocation.

#FIG. 1 illustrates the basic structure of one embodiment of a split-band encoder used in an encoder/decoder system incorporating forward-adaptive allocation. Filterbank 102 generates subband information in response to an input signal received from path 100. Allocation function 110 establishes allocation values in response to the input signal and passes the allocation values along path 111 to quantizer 104 and formatter 106. Quantizer 104 quantizes the subband information received from filterbank 102 using a quantization function adapted in response to the allocation values, and formatter 106 assembles the quantized subband information and the allocation values into an encoded signal having a format suitable for transmission or storage. The encoded signal is passed along path 108 to a transmission channel or storage device as desired.

#FIG. 2 illustrates the basic structure of one embodiment of a split-band decoder used in an encoder/decoder system incorporating forward-adaptive allocation. Deformatter 202 extracts quantized information and allocation values from an encoded signal received from path 200. The allocation values are passed along path 211 and to dequantizer 204. Dequantizer 204 generates subband information by dequantizing the quantized information received from deformatter 202 using a dequantization function adapted in response to the allocation values. Inverse filterbank 206 generates along path 208 an output signal in response to the dequantized subband information received from dequantizer 204.

#Alternate embodiments of the encoder and decoder are possible. For example, as shown in FIG. 3, a forward-adaptive encoder may establish allocation values in response to the subband information generated by filterbank 102. In yet another embodiment such as that shown in FIG. 13, allocation values may be established in response to both the input signal and the subband information. FIG. 13 also illustrates additional detail for allocation function 110, discussed in more detail below, in which excitation 301 generates an excitation pattern, thrhold 309 generates a masking threshold in response to the excitation pattern, and allocate 312 establishes allocation values which are passed along path 111 to quantizer 104 and formatter 106. Excitation 301 comprises spec rep 303 which generates a spectral representation of the input signal in response to either the input signal received from path 100 and/or subband information received from path 103, and spread func filter 306 which generates the excitation pattern by applying one or more filters to the spectral representation.