I guess that's true. But Tech has the ability to swap between voices almost instantly. While I think Em couldn't sound like himself from 99 if he tried to currently. I think Em's voice has just changed through the years (as it's supposed to, since he's human), and we have had an album to represent most of the phases so far.
Now, of course he has his obviously deliberate voices (like on Relapse), but he has a limit. I mean listen to him perform his old material now, it's like he's covering someone. I

whenever he tries performing My Name Is these days.
But I mean, just check out the amount of voices that Tech goes through in like 30 - 60 seconds here
http://youtu.be/OYmjdfMoGJE?t=5mOr the first 30 seconds of this
http://youtu.be/bIQjDfrJ6e8I just don't see Em ever showing that level of skill

i'm comin in, drivin my short bus
with this nose i don't need a torch up
bustin through, light the industry's porsche up
comin after who didn't support us...
imma change your brain bring
every wicked bit of strange to mainstream
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Tech N9ne #SpecialEffects2015