Cdim7

Cdim7 is C, Eb, Gb and A, a diminished seventh. The shape this page opens on is written xx1212, lowest string first.

Also written C°7, Co7 or C diminished 7. The same chord either way; which spelling you meet depends on who wrote the chart.

There are 7 common shapes for Cdim7 on the guitar, and 29 derived voicings in 4 families.

The common shapes, written lowest string first: xx1212, x34242, xx4545, 8x7878, 8-9-10-8-10-8, x-x-10-11-10-11, x-x-13-14-13-14.

Shell. Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top. Cdim7 has x3x242, 8x787x, x3787x, 8-6-7-11-x-x, 8-12-13-11-x-x.

Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. Cdim7 has 2312xx, xx1212, x3424x, xx4545, 5645xx, x6757x, xx7878, 8978xx.

Drop 3. The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped. Cdim7 has 2x121x, x3x242, 5x454x, x6x575, 8x787x, x-9-x-8-10-8, 11-x-10-11-10-x, x-12-x-11-13-11.

Open string. An open string left ringing against a fretted grip. Because it costs no finger, it sounds a note the closed shape has none left for -- a tension on top, or a pedal root underneath. Either a familiar grip with open strings added, or a shape so sparse the open strings carry the chord. These belong to their key rather than to a shape, so D, A, G and E have many and Eb a handful. Cdim7 has 56450x.

Tensions. A shell of Cdim7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (D), the 11 (F), the b13 (Ab) and the maj7 (B).

The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.