The most common and most likely answer to this crossword clue is the 10 letter word INFLECTION
I've seen this crossword clue in Independent
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More clues leading to the result INFLECTION
Buddy explains!
The straight part
We know that "Tone of voice" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tone of voice = inflection.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INFLECTION mean?
INFLECTION noun- (grammar) A change in the form of a word that reflects a change in grammatical function.
- A change in pitch or tone of voice.
- A change in curvature from concave to convex or from convex to concave.
- A turning away from a straight course.
- (optometry) diffraction