Standard of programme notes at Symphony Hall? (7,5)
I believe the answer is:
concert pitch
'standard of programme notes' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'symphony hall?' is the wordplay.
I cannot really understand how this works, but
'hall?' could be 'concert' (concert hall is a kind of hall) and 'concert' is present in the answer.
The remaining letters 'pitch' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'at' is the link.
(Other definitions for concert pitch that I've seen before include "A universally-agreed standard" , "state of alertness" , "state of readiness" .)