As played by tremulous musicians? (7)
I believe the answer is:
quavers
'tremulous musicians?' is the definition.
Although both the answer and definition are plural nouns, I cannot see how one could define the other.
'as played' is the wordplay.
'as' becomes 'qua' (I've seen this before).
'played' becomes 'vers' (I can't explain this - if you can you should give a lot more credence to this answer).
'qua'+'vers'='QUAVERS'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for quavers that I've seen before include "occupants of bar" , "Short musical notes" .)