interval
A minor second
AlowerB♭upperm21 half steps
One half step, written as a second: the smallest distance between two notes with different letters.
On the keyboard
What is true of it
A up a minor second is B♭: 1 half step, and 2 letters counting both ends.
Turn it upside down — put the A on top — and it becomes a major seventh. The two numbers always add to nine, and the two sizes to twelve.
It is a dissonance.
Every interval on A
A → Bmajor second · dissonanceA → Cminor third · imperfect consonanceA → C♯major third · imperfect consonanceA → Dperfect fourth · perfect consonanceA → D♯augmented fourth · dissonanceA → E♭diminished fifth · dissonanceA → Eperfect fifth · perfect consonanceA → Fminor sixth · imperfect consonanceA → F♯major sixth · imperfect consonanceA → Gminor seventh · dissonanceA → G♯major seventh · dissonance