AudioPad
AudioPad[audio,t] adds t seconds of silence to the end of audio.
AudioPad[audio,{t1,t2}] adds t1 seconds of silence to the beginning and t2 seconds to the end of audio.
AudioPad[audio,tspec,padding] pads using the value or method specified by padding.
Examples
AudioPad[ExampleData[{"Audio", "Violin"}], 2]Please visit the official Wolfram Language Reference for more details.