In many episodes of the original “Twilight Zone,” a 2-note interval is played. The second note is an octave lower than the first, plus a step upward, e.g. a C, followed by the next lower C#. It’s used to signify something creepy or malevolent. How did that interval come to mean that?
It sounds like you’re talking about a minor ninth, in which case, this (Scriabin’s Piano Sonata No. 9) might provide some background.
In the TZ version, the C is like a slow quarter note, and the C# is like a slow whole note. I can’t figure out what the interval is . . . it’s a half-step short of an octave.
Wouldn’t 11 semitones be a major 7th?
[QUOTE=Wikipedia]
The major seventh interval is considered one of the most dissonant intervals after its inversion the minor second.
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As for why, I suspect it is a diminished octave.
Missed 5 minute window.
IANAMT but I would think a diminished octave is the auditory version of the uncanny valley wherein our brain recognizes it as almost but not quite an octave.