I have a amp with a volume, treble, bass, middle. I know what they all do but there is another dial on there labeled mid shift, could someone tell me what it does?
i believe it just changes your eq. probably adds a little mid scoop or boost. i can't tell for sure though.
its most likely like how presence is for treble, this is for mids.
turn it down to "scoop" the mids, (for playing metal), turn it up for a more full sounding tone.

read the sticky: https://www.ultimate-guitar.com/forum/showthread.php?t=278232
scroll down to "amp settings/what the knobs do"

My Gear:
Fender American 60's Strat
Peavey Valveking Stack
Boss ME-50
Homebrew Crystal Bawl Wah
i have that on my amp as well.. what kind of amp is yours?? and yes what it does is it changes the mid range... either kinda boosts it up or turns it down