seriously, Key Signature effects every little thing in a piece of music…if ur playin a sharp and its supposed to be natural, then ur music is ruined….a piece of music is all about being in tune or in harmony and its supposed to sound lovely and memerizing…modulation is the key to perfect music…u also dont have to be gifted with perfect pitch to notice it…ive only been playin for 4 years and when im in band, I can tell if i am out of tune or playing the wrong sharp, flat, or natural, …..its all about listening

Only a person skilled in music would notice the key has changed. But you may notice a change in mood, color, or feeling of the peice.

ive often asked myself that same question. Then I’ve learned. Its all about the tone. For example, Tom Petty or Elton Johns voice have a horrible tone, where maybe Bing crosbys doesnt. A c chord on guitar sounds different than an f# chord. Some people transpose things in a different key for simplicitys sake. You cant play in F# on guitar and some people can’t sing in certain ranges either.