Using modified ten iron, his pitch changes little (7)

I believe the answer is:

intoner

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'his pitch changes little' is the definition.
The definition suggests a singular noun which matches the answer.

'using modified ten iron' is the wordplay.
'ten iron' can be anagrammed to 'INTONER'.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for intoner that I've seen before include "Someone who speaks monotonously - iron net (anag)" , "chanter" , "eg, a monk?" , "Participant in service" .)

I've seen this clue in The Guardian.

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