A vehicle audio system includes: a tune knob configured to select a frequency of a desired radio broadcast; a microcomputer configured to detect a broadcast frequency input through the tune knob and to determine an optimal sampling frequency of a full digital amplifier based on the detected broadcast frequency; a tuner configured to receive only a broadcast signal corresponding to the frequency selected through the tune knob; and the full digital amplifier configured to generate a digital signal by sampling the broadcast signal received by the tuner at the optimal sampling frequency determined by the microcomputer and to amplify and output the generated digital signal.