Perfect voice for a trio (6)

I believe the answer is:

treble

I'm a little stuck... Click here to teach me more about this clue!

'perfect voice' is the definition.
'treble' can be an answer for 'voice' (I've seen this before). I'm not sure about the 'perfect' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for treble that I've seen before include "Two-channel sound" , "High-frequency (radio control knob)" , "Soprano - multiply by three" , "Threefold; boy's voice" , "Threefold - singing voice" .)

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

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