def songAudio(self, pal, bpm=None):
        if bpm == None:
            bpm = pal._bpm
        total = self.baseDur(pal, bpm) + 3000 # 3 seconds for last note to play
        sound = AudioSegment.silent(total)
        curTime = 0
        for p in self._parts:
            paudio = p.getAudio(pal, bpm)
            sound = sound.overlay(paudio, curTime)
            curTime = curTime + p.baseDur(pal, bpm)
            print("curTime:",curTime)
        return sound