Overdriving Tape Heads - Ghostly LF Harmonics?

Does anyone know where I can get a good thorough analysis of tape distortion?

During my brief stay at GVSU, we read a text that said that there are certain low frequency harmonics that will show up soon after overdriving tape heads. These LF harmonics somehow corresponded to both the amount of clipping and also the HF content at the time of clipping. Or something like that.

Haven't seen those notes around in a few years, I'd love to refresh on the subject.

here is an AES paper on even order harmonic distortion in tape recording..

http://www.aes.org/aeshc/docs/3mtape/soundtalk/soundtalkbull03.pdf

JFR magnetics info here(lot of info)
http://www.jrfmagnetics.com/tapeheadintro.html

hope that helps some...