i cant watch the vid, school blockings ftl... but im guessing its done with a talk box
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its not processed exactly, its just a recording of him singing an octave higher playing at the same time to give that effect
yeah its all done in production. hard to tell exactly whether its an octave up like you said, he might have just 'copied and pasted' the vocals and then off-set them a little bit to make it sound like 2 people. you could always just get your buddy to talk with you, and it would probably sound similar.