Hey there, thanks for your question!

It's not obvious at all - just simply a choice some artists make.

Some singers feel tuning 1/2 step down suits their voice better, or the band might simply prefer the overall sound of the music. A guitarist might do this to loosen up the string tension - making bending and vibrato a little easier.

Hope this helps!

Mike

Originally Posted by: Navjot

I'm learning the song numb however, I cannot understand wh the tuning is down a half step?it might be pretty obvious but I'm pretty noobie and am leaning your song while ALSO learning guitar fundamentals 2