All of us have been taught that the standard tuning for a guitar is EBGDAE. Seldom does anyone teach you something known as the new standard tuning (NST)which had been developed by the King Crimson guitarist Robert Fripp. This was done near about the year 1983!It isn't that new now is it?
The NST is a variation of the classical theme. CGDAEB, that's the NST, and it goes well with metal & classical stuff.
it's from highest to lowest:
G4(<-- like the high G alternative on some 8 and 7 string guitar tunings)
E4(<-- originally this would be your highest string on a normal tuned guitar)
A3(<-- raise your G string's tuning by a whole step... obviously!!)
D3(<-- just leave your D string alone basically)
G2(<-- Lower your A string one whole step)
C2(<-- Drop your E string two whole steps..yeah now its fun..)
As you can see from the above tuning that its totally weird. Try it out,the fifths progression of the tuning is the same as that on a violin, cello, or other classical stringed instrument . It becomes really hard to try out thirds and sixths on this tuning, hence you are forced to try out some new
stuff and get some nice sounds out.