C7#9

C7#9 is C, E, G, Bb and D#, a seven sharp nine. The shape this page opens on is written x3234x, lowest string first.

Note by note. C is the root, E is the major third, G is the fifth, Bb is the flat seventh and D# is the minor third.

Also written C7(#9), C7+9 or C7♯9. The same chord either way; which spelling you meet depends on who wrote the chart.

There are 9 common shapes for C7#9 on the guitar, and 38 derived voicings in 4 families.

One note away. Change a single note of C7#9 and you have Cm7 (with one note taken away), Cm9 (with one note moved), C7 (with one note taken away), C7/G (with one note taken away), C9 (with one note moved) or C7b9 (with one note moved).

The common shapes, written lowest string first: x3234x, x35340, x65556, 8788xx, x78888, 8-10-8-9-8-11, 8-10-8-9-11-11, x-x-10-9-11-11, x-10-10-9-11-11.

Under the hand. 1 of the 9 shapes here sits in open position, and the first uses 1 open string with 1 left unplayed. 4 of the 9 need a barre. Together they cover the neck from the 2nd fret to the 11th.

Where it goes. C7#9 is a dominant with its tension raised, so it still points at F — harder than a plain seventh does, because the altered tones sit a semitone from where they are going.

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. C7#9 has x3234x, 8788xx, x-x-10-9-11-11.

Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. C7#9 has 0313xx, xx1310, x3234x, 8788xx, x-x-10-9-11-11, xx2546, 6625xx, x6855x.

Drop 3. The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped. C7#9 has 0x131x, 6x254x, x3x340, x6x556, 8x885x, x-7-x-8-11-8, 11-x-10-9-11-x, x-13-x-9-13-11.

Rootless. The root left to the bass player. Frees a finger for a tension. C7#9 has xx2343, x7888x, x-x-13-12-11-12, x1204x, x1x040, x6535x, x6x353, xx5856.

Tensions. A shell of C7#9, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (F#), the b13 (Ab) and the 13 (A).

What kind of chord this is. C7#9 is an altered chord — a dominant seventh with its fifth or ninth moved. altered dominant chords on every root, and what they are for.

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