Hello,
Found this instructive article about subnormals (called denormal numbers there):
http://www.google.nl/url?sa=t&rct=j&q=musicdsp%20denormal&source...
Subnormal numbers are a pain in the ass, they cause substantially increased CPU load without doing anything useful for audio DSP. Unfortunately it can happen in some Pd objects (notably [freeverb~]), and spoil the performance of a Pd patch. The article explains why subnormal numbers occur, and what can be done to eliminate or prevent them.
Katja