The ♭7 of D♭ is C♭
The ♭7 (flat seven, written b7) of D♭ (D flat, Db) is C♭ (C flat): a minor seventh above the root.
How to find it
Count letters first, the root included: D, E, F, G, A, B, C. A 7th lands on C.
Then the sound: a minor seventh is 10 semitones above D♭, and the C that is 10 semitones up is C♭.
That is why it is C♭ and not B: B is the same key on the piano, but from D♭ it would be a 6th, not a 7th.
Where you meet it
The ♭7 is the 7th of the dominant chord and of the minor seventh chord, and the note that turns the major scale into Mixolydian.
In D♭7:
D♭ · F · A♭ · C♭
The ♭7 in every key
| Key | The ♭7 |
|---|---|
| C | B♭ |
| G | F |
| D | C |
| A | G |
| E | D |
| B | A |
| F♯ | E |
| D♭ | C♭ |
| A♭ | G♭ |
| E♭ | D♭ |
| B♭ | A♭ |
| F | E♭ |
Every degree of D♭
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