Encoding method, decoding method, encoder, decoder, program, and recording medium

An encoder configured to encode, with a predetermined number of bits, a frequency-domain sample sequence derived from an acoustic signal in a predetermined time interval, the encoder comprising:

• processing circuitry configured to
• perform an encoding step of encoding, by variable-length encoding, an integer value u(n) corresponding to x(n)/g obtained by dividing a value x(n) of each sample n in the frequency-domain sample sequence by a gain g to generate a variable-length code, wherein every integer value u(n) is encoded regardless of whether the obtained integer value u(n) is 0 or not;
• and
• perform an error encoding step of encoding information indicating whether each of quantization errors r(n)=x(n)/g−u(n) in the encoding step is positive or negative, 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 quantization errors r(n), quantization errors r(n) whose corresponding integers are not 0 are encoded with priority in the error encoding step.