Electronic instrument designer keeping in low sound (6)

I believe the answer is:

mooing

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'electronic instrument designer keeping in low sound' is the definition.
I can't tell whether this definition defines the answer.

'keeping in low sound' is the wordplay.
'keeping' means one lot of letters goes inside another (some letters kept inside).
'low sound' becomes 'moog' (I can't explain this - if you can you should believe this answer much more).
'in' inserted within 'moog' is 'MOOING'.

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I've seen this clue in The Independent.

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