Record playing in calm, calm water (8)
I believe the answer is:
millpond
'calm water' is the definition.
'record playing in calm' is the wordplay.
'record' becomes 'lp' (L-P is an example).
'playing' becomes 'on'.
'in' means one lot of letters goes inside another.
'calm' becomes 'mild' (I've seen this before**).
'lp'+'on'='lpon'
'lpon' going within 'mild' is 'MILLPOND'.
(Other definitions for millpond that I've seen before include "Proverbially placid water" , "this is traditionally flat" .)