The ♭2 of B♭ is C♭
The ♭2 (flat two, written b2) of B♭ (B flat, Bb) is C♭ (C flat): a minor second above the root.
How to find it
Count letters first, the root included: B, C. A 2nd lands on C.
Then the sound: a minor second is 1 semitones above B♭, and the C that is 1 semitones up is C♭.
That is why it is C♭ and not B: B is the same key on the piano, but from B♭ it would be an unison, not a 2nd.
Where you meet it
The ♭2 is a half step above the root. It is the note that makes Phrygian sound dark, and the root of the ♭II7 chord, the tritone substitute for the V7 that resolves to B♭.
In the scale B♭ Phrygian:
B♭ · C♭ · D♭ · E♭ · F · G♭ · A♭
The ♭2 in every key
| Key | The ♭2 |
|---|---|
| C | D♭ |
| G | A♭ |
| D | E♭ |
| A | B♭ |
| E | F |
| B | C |
| F♯ | G |
| D♭ | E𝄫 |
| A♭ | B𝄫 |
| E♭ | F♭ |
| B♭ | C♭ |
| F | G♭ |
Every degree of B♭
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