Disclosed is a unified speech and audio coding (USAC) audio signal encoding/decoding apparatus and method for digital radio services. An audio signal encoding method may include receiving an audio signal, determining a coding method for the received audio signal, encoding the audio signal based on the determined coding method, and configuring, as an audio superframe of a fixed size, an audio stream generated as a result of encoding the audio signal, wherein the coding method may include a first coding method associated with extended high-efficiency advanced audio coding (xHE-AAC) and a second coding method associated with existing advanced audio coding (AAC).