An audio device includes a processor, a storage unit, an audio processing module, a silence detection circuit, a condition determining circuit, a direct current (DC) level bias circuit and an appending circuit. The audio device generates identification data, control signals, and original audio signals. The silence detection circuit detects silence segments of the original audio signals, and generates driving signals if the silence segments are detected. Then the condition determining circuit determines if the identification data needs to be appended into the silence segments according to the driving signals and the control signals, and outputs the identification data in DC signal form if the identification data needs to be appended into the silence segments. After DC voltage level of the identification data in DC signal form is biased, the appending circuit appends the biased identification data into the silence segments of the original audio signals.