Start of Chopin -- it's in authentic concert (7)
I believe the answer is:
recital
'concert' is the definition.
(thesaurus)
'start of chopin it's in authentic' is the wordplay.
'start of' says to take the initial letters.
'it's' becomes 'it' (I've seen this in other clues**).
'in' is an insertion indicator.
'authentic' becomes 'real' (I've seen this before).
The first letter of 'chopin' is 'c'.
'c'+'it'='cit'
'cit' going within 'real' is 'RECITAL'.
(Other definitions for recital that I've seen before include "Public musical performance" , "Public performance of music" , "Verbal account" , "Musical entertainment or a long account" , "Performance, usually musical" .)