The Open G/C Add4 tuning is a deeply resonant and versatile setup, primarily built around a powerful G major chord with a low C bass. This configuration crafts a rich, full open sound that distinctly leans towards a C major tonality, often evoking a Cmaj7 or Cmaj9 feel due to the interplay of the C root, G (perfect fifth), B (major seventh), and D (major ninth). It provides a strong, drone-like foundation, making it exceptional for various musical styles, particularly folk, blues, and rock. Its design also naturally facilitates expressive slide guitar playing and simplifies chordal work, allowing for easy one-finger bar chords across the fretboard.

Technically, this tuning sets the open strings to C2 G2 D3 G3 B3 D4. When all strings are strummed open, the combination of C, G, B, and D notes creates a complex, harmonious sound. The top five strings (G2 D3 G3 B3 D4) perfectly form a G major chord (G-B-D) with octaves, while the lowest string anchors the harmony with a robust C root. This unique arrangement offers both the familiar robustness of an open G chord and the sophisticated harmonic richness of a C major 7th or 9th chord without requiring any fretting. The 'Add4' in the name suggests an intentional emphasis on the D note, perhaps as an added fourth in certain theoretical contexts, contributing to the tuning's overall full and intricate sound.

Open Chord Possibilities:

• Strumming all strings open immediately yields a rich G major chord over a C bass (G/C), which can also be interpreted as a Cmaj9 (omitting the 3rd).
• Barring across any single fret will instantly produce a movable major chord shape, making this tuning incredibly versatile for rhythm guitarists. For example, barring all strings at the 2nd fret creates a D major chord over an E bass (D/E), while a bar at the 5th fret yields a G major chord over an A bass (G/A).
• The tuning is also highly conducive to drone notes and creative melodic exploration within both G major and C major scales, enabling the discovery of unique arpeggios and voicings.

How to Tune:

To achieve the Open G/C Add4 tuning, follow these steps from standard E Standard tuning (E A D G B E):

• String 6 (Low E): Tune down 4 semitones from E2 to C2. Please note: Tuning down 4 semitones is a significant alteration in string tension; for optimal playability and tone, a heavier gauge string is advised for this string.
• String 5 (A): Tune down 2 semitones from A2 to G2.
• String 4 (D): Keep as is; no change (0 semitones). This string remains at D3.
• String 3 (G): Keep as is; no change (0 semitones). This string remains at G3.
• String 2 (B): Keep as is; no change (0 semitones). This string remains at B3.
• String 1 (High E): Tune down 2 semitones from E4 to D4.

String 6: C2

String 5: G2

String 4: D3

String 3: G3

String 2: B3

String 1: D4