Sound volume requiring adjustment of dial (5)
I believe the answer is:
valid
'sound' is the definition.
(similar in meaning)
'volume requiring adjustment of dial' is the wordplay.
'volume' becomes 'v' (abbreviation for volume in book titles).
'requiring' says to put letters next to each other.
'adjustment of' indicates anagramming the letters (I've seen this in other clues).
'dial' is an anagram of 'alid'.
'v'+'alid'='VALID'
(Other definitions for valid that I've seen before include "Well-founded" , "Binding" , "Officially acceptable" , "Legally acceptable and sound" , "Still legally acceptable" .)