I'm speaking from my hearing experience here and I wasn't able to pick up the 2nd nor the 3rd harmonic out of the fundamental on a -60dB difference
My thresholds are based on the sources I've cited. Earlier in this thread, @mitchco brought up the topic of what realistic thresholds for an average Joe could be. Nothing wrong with the discussion, but I don't really have any comments on it and my thresholds will remain the same.
Or you are probably referring to dynamic as the difference between the loudest and the barely perceivable sound
Anything below -120 dBFS is inaudible, be it noise, distortion, or imaginary Head-Fi concepts.