[PD] a peak detector ?

Hello, I need help with that problem: I have a audio file playing from readsf~, this audio contains silence that I need to detect. I used a threshold to do so, but it seems not to work. After many tests I realise that the signal out of readsf~ vary form -1 to 1 and outputs 0 when there is no sound or silence. Therefore it found impossible to use threshold directly after readsf~. I assume this is something I do wrong because I do not understand that very much. I tried then to use env~ that triggers a bang when above 0, I guess this solution is not very precise and I wonder how much delay there is between the real silence and the time env~ sends a 0. The solution to my problem would be a peakdetector maybe. Are there any ? Thanks