From the outside, urban disco noise is wretched (6)

I believe the answer is:

undone

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'wretched' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I can't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for undone that I've seen before include "Not bound" , "Ruined - no longer fastened" , "Not finished; untied" , "Reversed" , "Ruined; not tied" .)

I've seen this clue in The Irish Times.

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