interval
G♭ augmented fourth
G♭lowerCupperA46 half steps
A perfect fourth widened by a half step. Same sound as the diminished fifth, different letter, different behaviour.
On the keyboard
What is true of it
G♭ up a augmented fourth is C: 6 half steps, and 4 letters counting both ends.
Turn it upside down — put the G♭ on top — and it becomes a diminished fifth. The two numbers always add to nine, and the two sizes to twelve.
It is a dissonance.
Six half steps can be written two ways: G♭ to C is a fourth, G♭ to D♭♭ is a fifth. They sound the same and behave differently.
Every interval on G♭
G♭ → A♭♭minor second · dissonanceG♭ → A♭major second · dissonanceG♭ → B♭♭minor third · imperfect consonanceG♭ → B♭major third · imperfect consonanceG♭ → C♭perfect fourth · perfect consonanceG♭ → D♭♭diminished fifth · dissonanceG♭ → D♭perfect fifth · perfect consonanceG♭ → E♭♭minor sixth · imperfect consonanceG♭ → E♭major sixth · imperfect consonanceG♭ → F♭minor seventh · dissonanceG♭ → Fmajor seventh · dissonance