Decidedly shaky, musically speaking (7)

I believe the answer is:

tremolo

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'speaking' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

I don't understand how the remainder of the clue works.

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(Other definitions for tremolo that I've seen before include "Quivering musical effect" , "Paganini's effect" , "Vibrating musical effect" , "Vibrato effect" , "Musical wavering effect" .)

I've seen this clue in The Irish Independent.

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