Expresses requirements for a choir (6)

I believe the answer is:

voices

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This could be a double definition.

'expresses requirements' is the first definition.
'voices' can be an answer for 'expresses' (voicing is a kind of expressing). I am unsure of the 'requirements' bit.

'choir' is the second definition.
(thesaurus)

'for a' acts as a link.

Can you help me to learn more?

(Other definitions for voices that I've seen before include "Sounds of people" , "They may be audible" , "Expressed opinions; utters" , "Speaks" .)

I've seen this clue in The Globe and Mail.

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