Something to sing about when smelling it? (4)

I believe the answer is:

niff

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'smelling it?' is the definition.
I can't tell whether this definition defines the answer.

'something to sing about when' is the wordplay.
'something to sing' becomes 'nf' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'when' becomes 'if'.
'nf' enclosing 'if' is 'NIFF'.

Can you help me to learn more?

(Other definitions for niff that I've seen before include "a stink" , "Hum" .)

I've seen this clue in the Evening Standard.

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