Instrumental accompaniment requiring top billing was too regularly overlooked (8)

I believe the answer is:

obligato

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'instrumental accompaniment' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

'top billing was too regularly overlooked' is the wordplay.
'regularly overlooked' indicates alternate letters (letters removed at regular intervals).
'top'+'billing'+'was'+'too'='topbillingwastoo'
The alternating letters of 'topbillingwastoo' are 'OBLIGATO'.

'requiring' is the link.

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I've seen this clue in The Telegraph.

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