Encoding method, decoding method, encoder, decoder, program, and recording medium
In encoding, a frequency-domain sample sequence derived from an acoustic signal is divided by a weighted envelope and is then divided by a gain, the result obtained is quantized, and each sample is variable-length encoded. The error between the sample before quantization and the sample after quantization is quantized with information saved in this variable-length encoding. This quantization is performed under a rule that specifies, according to the number of saved bits, samples whose errors are to be quantized. In decoding, variable-length codes in an input sequence of codes are decoded to obtain a frequency-domain sample sequence; an error signal is further decoded under a rule that depends on the number of bits of the variable-length codes; and from the obtained sample sequence, the original sample sequence is obtained according to supplementary information.
1. An encoding method for encoding, with a predetermined number of bits, a frequency-domain sample sequence derived from an acoustic signal in a predetermined time interval, the encoding method comprising:
an encoding step of encoding, by variable-length encoding, an integer obtained by dividing a value of each sample in the frequency-domain sample sequence by a gain to generate a variable-length code, wherein every integer is encoded regardless of whether the obtained integer is 0 or not;
an error calculation step of calculating error values each obtained by subtracting the integer obtained by dividing the value of each sample in the frequency-domain sample sequence by the gain from a value of a sample obtained by dividing the value of each sample in the frequency-domain sample sequence by the gain; and
an error encoding step of encoding information indicating whether each of the error values is positive or negative with one bit, with a number of surplus bits obtained by subtracting a number of bits of the variable-length code from the predetermined number of bits to generate error codes, the surplus bits being saved by performing the variable-length encoding,
wherein, among said error values, error values whose corresponding integers are not 0 are encoded with priority in the error encoding step.
2. The encoding method according to claim 1 , wherein
a value determined based on the integer is regarded as an absolute value of a reconstructed value, the absolute value of the reconstructed value is regarded as a reconstructed value corresponding to each of said error values when the each of said error values is positive, and a value obtained by subtracting the absolute value of the reconstructed value from 0 is regarded as a reconstructed value corresponding to each of said error values when the each of said error values is negative, and
when the number of surplus bits is larger than a number of error samples constituting a sequence of error values, information indicating whether a value obtained by subtracting the reconstructed value corresponding to each error sample from the value of the error sample is positive or negative is further encoded with one bit in the error encoding step.
3. The encoding method according to claim 2 , wherein a first absolute value of a first reconstructed value obtained when a first integer is not 0 is larger than a second absolute value of a second reconstructed value obtained when a second integer is 0.
4. A non-transitory computer-readable recording medium having stored thereon a program for causing a computer to execute the steps of the method according to claim 1 .
5. An encoder for encoding, with a predetermined number of bits, a frequency-domain sample sequence derived from an acoustic signal in a predetermined time interval, the encoder comprising:
circuitry configured to
encode, by variable-length encoding, an integer obtained by dividing a value of each sample in the frequency-domain sample sequence by a gain to generate a variable-length code, wherein every integer is encoded regardless of whether the obtained integer is 0 or not;
calculate error values each obtained by subtracting the integer obtained by dividing the value of each sample in the frequency-domain sample sequence by the gain from a value of a sample obtained by dividing the value of each sample in the frequency-domain sample sequence by the gain; and
encode information indicating whether each of the error values is positive or negative with one bit, with a number of surplus bits obtained by subtracting a number of bits of the variable-length code from the predetermined number of bits to generate error codes, the surplus bits being saved by performing the variable-length encoding,
wherein the circuitry encodes, among said error values, error values whose corresponding integers are not 0 with priority.