Barbirolli's lead is helpful for musicians (8)

I believe the answer is:

bassists

I'm a little stuck... Click here to teach me more about this clue!

'for musicians' is the definition.
(I've seen this before)

'barbirolli's lead is helpful' is the wordplay.
I cannot really see how this works, but
'is' is within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for bassists that I've seen is " musicians".)

I've seen this clue in The Times.

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