Here recently I find myself using the pinch harmonic technique (refering to the fleshy part of your thumb) while playing mostly power chords. Im wondering if anyone really uses this technique to alter their tone...because there is a huge difference. Even if you subtley use this technique and dont go for the whole "squeal" sound

It also seems to work while playing fast rhythms mixed with fast leads.

i do it somtimes but not to any great extent

I only use that technique on acoustic finger-picking style.

http://metaltabs.com/forum/showthread.php?t=1118

There's already a thread for pinch harmonics. Look in the sticky.

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