Bflat

B-flat, written B♭, is a pitch class in Western music. It is a semitone above A and a semitone below B natural, and corresponds to the black key to the left of B on a standard piano. In the standard concert pitch where A4 equals 440 Hz, B♭4 is about 466 Hz; frequencies rise or fall by a factor of two with each octave.

Enharmonics and notation: B♭ is enharmonically equivalent to A♯. In key signatures, B♭ major has two flats (B♭ and E♭), and B♭ minor has five flats (B♭, E♭, A♭, D♭, G♭). The note can appear in various octaves and can be represented with different spellings in different keys or harmonic contexts.

Transposing instruments: Many wind instruments are pitched in B♭, meaning they are transposing instruments. When they play a written C, the concert pitch sounds as B♭, so these instruments sound a whole step lower than written. Common examples include the B♭ trumpet and the B♭ clarinet, which are designed to align with concert pitch when transposed.

Usage and theory: In music theory, the B♭ major scale comprises B♭, C, D, E♭, F, G, A, B♭. The B♭ natural minor scale comprises B♭, C, D♭, E♭, F, G♭, A♭, B♭. The key of B♭ is widely used across classical, jazz, and contemporary music due to its comfortable fingering on many instruments.