Performing during banal interval (7)
I believe the answer is:
tritone
'interval' is the definition.
(I know that tritone is a type of interval)
'performing during banal' is the wordplay.
'performing' becomes 'on' (as in being on stage).
'during' indicates putting letters inside.
'banal' becomes 'trite' (I've seen this in another clue).
'on' inserted inside 'trite' is 'TRITONE'.
(Other definitions for tritone that I've seen before include "Augmented fourth" , "long interval?" , "Musical interval" .)