The most common and most likely answer to this crossword clue is the 7 letter word COPLAND
C
O
P
L
A
N
D
More clues leading to the result COPLAND
- Composer available from PC World?
- Bobby left with American composer
- Notes expert in police state
- Idea entertained by bogus composer
- Creator of notes in police station?
- Composer seen in police state
- Composer's program swallowed by fish
- Rodeo composer’s arrangement swallowed by fish
- American composer and officer arrive at Heathrow, maybe
- American music writer in police state?
Buddy explains!

The straight part
We know that "Notes expert" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case notes expert = copland.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.