Lower terribly crude note (6)
I believe the answer is:
Here is my best explanation:
'lower' is the definition.
(I've seen this before)
'terribly crude note' is the wordplay.
'terribly' indicates an anagram.
'note' becomes 'e' (musical note).
'crude' is an anagram of 'reduc'.
(Other definitions for reduce that I've seen before include "Make smaller or take off weight", "Bring down", "Shrink", "Lessen", "Subjugate; make (sauce) thicker", "Take off weight", "'Cut down, abridge (6)'", "subdue", "Boil down or cut back" and "Make smaller or slimmer".)