Использование pydub :
from pydub import AudioSegment
pad_ms = 1000 # milliseconds of silence needed
silence = AudioSegment.silent(duration=pad_ms)
audio = AudioSegment.from_wav('you-wav-file.wav')
padded = audio + silence # Adding silence after the audio
padded.export('padded-file.wav', format='wav')
AudioSegment
объекты неизменны