Sound a group of singers had picked up (8)
I believe the answer is:
acquired
'sound a group of singers' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I can't see?
'had picked up' is the wordplay.
I cannot really understand how this works, but
'had' could be 'd' (I've seen this in other clues) and 'd' is located in the answer.
The remaining letters 'acquire' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for acquired that I've seen before include "Took (on)" , "Got hold of" , "Came by, obtained" , "'Got, gained (8)'" , "Bought" .)