Quaver from soprano captivating musician, initially (7)

I believe the answer is:
tremble
'quaver' is the definition.
(thesaurus)
'soprano captivating musician initially' is the wordplay.
'soprano' becomes 'treble' (synonyms).
'captivating' means one lot of letters goes inside another (inserted letters are captured or captivated).
'musician initially' becomes 'm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'treble' enclosing 'm' is 'TREMBLE'.
'from' acts as a link.
Can you help me to learn more?
(Other definitions for tremble that I've seen before include "Quakers do this" , "Show fear" , "Shudder" , "Shiver or jerk quickly" , "Shiver, quake" .)
