the engineer does mix/master,you're correct...a 'producer' creates or helps create the song..there's different types of producers..you have beatmakers that are also songwriter producers...you got producers' like Puffy that tells you what he wants and get's an artist to put it down..then you got beatmakers that play engineer/producer that record vocals and add appropriate sound effects and adjust levels and customizes the beat around lyrics and gives his opinion on an artist's performance during recording


of course,the songwriters got bigger egos but thas cool..in rap ESP indie rap you're hopefully dealing with artists that are nice with it and don't need nobody else's lyrics imo ..the last producer i described is that dude ESP if he got hot beats...thas how bangers are made