Lot more about variation in pitch (7)
I believe the answer is:
tremolo
'variation in pitch' is the definition.
'lot more about' is the wordplay.
'about' indicates an anagram.
'lot'+'more'='lotmore'
'lotmore' anagrammed gives 'TREMOLO'.
(Other definitions for tremolo that I've seen before include "Vibrato effect" , "Unsteady effect" , "Musically shivering" , "Wavering effect in music" , "A vibrating effect in music" .)