Singer joining vocal together (4)

I believe the answer is:

alto

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'singer' is the definition.
(alto is a kind of singer)

'joining vocal together' is the wordplay.
'ALTO' is hidden in amongst the letters.
However, I'm uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for alto that I've seen before include "Singing voice between tenor and soprano" , "The highest adult male singing voice" , "Counter-tenor or contralto" , "Singer's hidden inside chemical toilet" , "Member of choir" .)

I've seen this clue in The Sun.

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