In a signal processing method to compress digital audio data by a block floating process, digital signal encoding/decoding apparatuses prevent deterioration of sound quality of the digital audio signal and improve the compression ratio of the digital audio signal when the digital audio signal is converted on a frequency axis per predetermined time frame, and data on the frequency axis is then divided into a plurality of blocks to be recorded, otherwise, bits are allocated per block to compress the digital audio signal for minimizing transmitted parameters. Also, encoding/decoding methods are provided to enable highly efficient encoding/decoding without recording or transmitting word length, allowing one to obtain a high-quality audio signal by allocating bits conventionally held by the word length to hold quantization data of a spectrum signal.