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Be at the root of crow calls, by the sound of it (5)

Ross

I believe the answer is:

cause

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'sound of it' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for cause that I've seen before include "why some people fight" , "It brings about an effect" , "Make happen; something deserving support" , "Grounds" , "Producer of an effect" .)

I've seen this clue in the Sydney Morning Herald.
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