Beginning of sound at the film studio (5)
I believe the answer is:
onset
'beginning of sound' is the definition.
'onset' can be an answer for 'beginning' (onset is a kind of beginning). I'm not certain of the 'of sound' bit.
'the film studio' is the wordplay.
'the film' becomes 'on' (I can't explain this - if you can you should give a lot more credence to this answer).
'studio' becomes 'set' (as in a TV set).
'on'+'set'='ONSET'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for onset that I've seen before include "Beginning (of something often unpleasant)" , "Start - notes (anag)" , "Stone (anag)" , "Start, beginning" , "Advent" .)