First part of recital: one very loud piece of music (4)
I believe the answer is:
riff
'piece of music' is the definition.
(riff is a kind of piece of music)
'first part of recital one very loud' is the wordplay.
'first part of' says to take the initial letters.
'one' becomes 'i' (Roman numeral**).
'very loud' becomes 'ff' (musical abbreviation).
The initial letter of 'recital' is 'r'.
'r'+'i'+'ff'='RIFF'
(Other definitions for riff that I've seen before include "Short repeated phrase (in jazz, etc)" , "Short series of chords in jazz" , "Short repeated jazz figure" , "repeating phrase" , "Ostinato common in jazz, rock, etc" .)