Perform well in, increasing gradually in volume (8)
I believe the answer is:
swelling
'increasing gradually in volume' is the definition.
'swelling' can be an answer for 'volume' (thesaurus). I'm unsure of the 'increasing gradually in' bit.
'perform well in' is the wordplay.
'perform' becomes 'sing' (to perform a song).
'in' indicates putting letters inside.
'sing' placed around 'well' is 'SWELLING'.
Can you help me to learn more?
(Other definitions for swelling that I've seen before include "increasing in volume" , "Growth" , "area suffering inflation" , "Bulge" , "Lump" .)