#1
I was looking at some guitar rigs for various artists, in particular Kings of Leon and Incubus guitarists use 2 or more of the same pedal, such as verbzilla/whammys/ overdrives, I have never really heard of using two of the same pedal consecutively at the same time, do they use them simultaneously?
#2
They likely had a split channel for each set of effects, probably operated via footswitch or rack.

Alternatively, I have seen people use multiple wah effects (not simultaneously). Each wah has a unique sound and feel, you can switch them up depending on what color you want to give your sound.
#3
I use two tremolos, set to different depths, at once to get really cool rhythms going. I've also heard of people using cascading overdrives to get the dirt they want. Wouldn't be too much of a stretch to use two of the same one, people run boosters or ODs into other dirt pedals all the time.
#5
I use 2 boss dd-7s one in the loop one out front also use 2 isp decimators same way?
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#6
Most of the time they use the pedals on different settings for different songs, so instead of changing one there they use multiple... Sigh, things you can do when you're rich
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