Bartender - Vol. 10 Ch. 76 - Fluctuat Nec Mergitur (Part 2)

[MangaDex]

 

[Beregorn]

9 octaves seems an exaggeration, but the current world record is 10; in addition, the same guy also got the record for the lowest note, two octaves below what he did for the extension record. It would not be unreasonable to think that 12 may be possible.
On the other hand, most people will have trouble doing more than 2...