If the seventh degree of a scale is lowered one half step, you have a b7: a tone used in dominant 7th and minor 7th chords.
If the seventh degree of the scale is lowered by one full step, it becomes a bb7: a tone used in a diminished 7th chord.
Flat 7 (diminished 7th, b7)
The 7th degree of a scale lowered by a half (b7) or whole (bb7) step
Updated over 4 years ago