Thanks for your question. The omx objects use a somewhat curious "humanized" parameter value scheme that we should put more effort into documenting. For the threshold of omx.peaklim~ you are correct that 0-100 is an arbitrary range of values that are mapped over the range -24 to 24dB. There is no way to set the parameter outside of this dB range. Ideally, it would be nice if you could do things such as set the threshold in dB directly.