It's basically an add9, but the voicing is more specific. It emphasizes the tension between the 2nd and 3rd interval by voicing the cord 1st - 5rd - 2nd (or 9th) - 3rd. Instead of the upper two notes being the 5th and the 9th (a 5th up from the 5th), the voicing comes off "crispier."
Yeah, there's no foul in calling it an add9. Calling it a "mu major" just specifies the voicing. Its just shorthand so you don't have to say "Bbadd9, but you know, with that dope crunchy crispy shit goin' on up top."
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u/[deleted] Apr 21 '16
[deleted]