What key is What A Diff'rence A Day Made in?

A# (Bb) major requires barre chords rooted at fret 1 on the A string or fret 6 on the E string. Despite the barre demands, it is a common key in funk, New Orleans R&B, and brass band music. The open D string can ring as the major third for added color. A# is a intermediate-level key on guitar because the open D string is the major 3rd of Bb, adding a bright color if allowed to ring. Expect to rely on barre chords throughout, which builds hand strength and unlocks the entire fretboard.

Voice Leading

The bass line moves through C to F (ascending perfect fourth), F to A# (ascending perfect fourth), A# to C# (ascending minor third), C# to F (ascending major third), F to A (ascending major third), A to D (ascending perfect fourth), D to G (ascending perfect fourth), G to C (ascending perfect fourth), C to F (ascending perfect fourth), F to A# (ascending perfect fourth), A# to D# (ascending perfect fourth), D# to D# (ascending unison). The root motion by larger intervals (fourths and fifths) gives each chord change a strong, decisive character. When the progression loops, the bass returns from D# to C by minor third.

Scales for Improvisation

A# major pentatonic works because every note is either a chord tone or a safe passing tone — there are no avoid notes. For soloing, this means you can play freely without clashing. Over dominant seventh chords, A# Mixolydian adds the flat seventh for an authentic blues-rock edge.

swing2/2 · 33 bars · Form: ABAC

Chords: Dom7, Fa7, La♯, Do♯dim7, Fa7♯5, Lam7, Re7, Solm7, Do7, Fam7, La♯7, Re♯Maj7, Re♯m6.

Scales for Improvisation La# bebop, La# bebop major.