Precision ultimately lacking in improvised clarinet performance (7)
I believe the answer is:
recital
'performance' is the definition.
(recital is a kind of performance)
I can't explain the remainder of the clue.
(Other definitions for recital that I've seen before include "Musical entertainment or a long account" , "Public performance by a solo musician" , "17 performance, for example" , "Solo music performance" , "gig" .)