Stop briefly in grotto for musical intervals (7)

I believe the answer is:

octaves

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'musical intervals' is the definition.
(octave is a kind of musical interval)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for octaves that I've seen before include "Musical intervals of eight notes" , "Eight-note spans" , "lot of notes" , "8-note hand spans (mus.)" , "Groups of eight consecutive notes on a scale" .)

I've seen this clue in The Irish Times.

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