C7(b13) chord on cavaquinho
C7(b13) is the dominant flat thirteenth chord: C, E, G, Bb and Ab (1–3–5–b7–b13). On cavaquinho, the diagram shape is 6 5 5 8, with Ab in the bass.
On the cavaquinho, four steel strings tuned D–G–B–D pack the chord into a small, bright space — every finger counts. In this C7(b13) voicing the bass is Ab and the shape runs from fret 5 to 8. Because this instrument has fewer strings than C7(b13) has notes, one note, usually the fifth, is normally dropped without losing the chord's identity. Its four steel strings give a bright, sharp attack that cuts through the mix and drives the beat.
Notes and formula of C7(b13)
Notes in C7(b13): C – E – G – Bb – AbFormula: 1 – 3 – 5 – b7 – b13In the formula, the numbers count steps of the major scale starting from the note that names the chord; "b" lowers a half step, "#" raises one — and a slash names the bass note.
Where to use it
A dark resolution, especially to a minor chord.
See also
Part of the Altered dominants family.