The most common and most likely answer to this crossword clue is the 9 letter word SEMITONES
I've seen this crossword clue in Financial Times
S
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More clues leading to the result SEMITONES
Buddy explains!

The straight part
We know that "regular intervals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case regular intervals = semitones.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SEMITONES mean?
SEMITONES noun- The musical interval equal (exactly or approximately) to half a tone or one-twelfth of an octave
- Any of the pitches of the chromatic scale