fourth
musical interval spanning four staff positions
diminished fourth
musical interval produced by narrowing a perfect fourth by a chromatic semitone (e.g. from C♯ to F or from C to F♭); enharmonically equivalent to a major third
perfect fourth
musical interval spanning four staff positions and five semitones, with a frequency ratio of approximately 4:3=1.333… (in equal temperament, ¹²√2⁵ = 1.335…)
major fourth
musical interval with a frequency ratio of 11:8=1.375, not present in the 12-tone scale but present in e.g. quarter tone scales, named by Ivan Wyschnegradsky
augmented fourth
musical interval spanning four staff positions and 6 semitones