An audio signal encoding method and apparatus and an audio signal decoding method and apparatus are provided. The audio signal encoding method includes: transforming an audio signal into a signal of a frequency domain; extracting semantic information from the audio signal; variably reconfiguring one or more sub-bands included in the audio signal by segmenting or grouping the one or more sub-bands using the extracted semantic information; and generating a quantized bitstream by calculating a quantization step size and a scale factor with respect to a reconfigured sub-band of the one or more sub-bands.