Internal soundgen function called by getDuration.
.getDuration(audio, silence = 0.01, rms = list(windowLength = 20, step = 5))a list returned by readAudio
leading and trailing sections quieter than this proportion of
maximum RMS amplitude are removed when calculating
duration_noSilence (NULL = don't calculate duration_noSilence
to save time)
a list of control parameters passed to getRMS