This intriguing 7-string guitar tuning, aptly named "Open G/C add6", presents a rich and harmonically complex soundscape. It's a fascinating variant that blends the power of a low C with the bright resonance of G major, further extended by a high E. When strummed open, this tuning immediately evokes a sense of grandeur and fullness, creating a sound that hovers between a Cmaj13 and a G major chord with a strong C bass. Its unique construction makes it highly suitable for expansive open-string arpeggios, drone-based music, and slide guitar techniques, where its inherent harmonic quality can truly shine.

Technically, the open strings are tuned to C2 G2 D3 G3 B3 D4 E4. This arrangement provides a powerful foundation with the lowest string at C2. Moving up, strings 6, 3, and 2 (G2, B3, D4) form a clear and resonant G Major triad, which gives the tuning its "Open G" character. The C2 on the 7th string acts as a strong sub-dominant or tonic pedal, while the D3 and G3 strings fill out the harmonic space. The E4 on the highest string adds a major third relative to C, or a major sixth relative to G, contributing to the "add6" quality or completing a Cmaj13 chord (C-E-G-B-D-E, with the E and B present in the tuning notes).

The intervallic relationships are quite harmonious:

• String 7 (C2) to String 6 (G2): Perfect 5th
• String 6 (G2) to String 5 (D3): Perfect 5th
• String 5 (D3) to String 4 (G3): Perfect 4th
• String 4 (G3) to String 3 (B3): Major 3rd
• String 3 (B3) to String 2 (D4): Minor 3rd
• String 2 (D4) to String 1 (E4): Major 2nd

This careful spacing creates a full-bodied sound where many intervals are consonant. When strummed open, a Cmaj13 chord is effectively produced, offering a rich, jazz-infused or highly resonant contemporary sound. Furthermore, a simple barre across all seven strings will yield a different major chord based on the fret. For instance, barring at the 2nd fret would produce a Dmaj13, and at the 5th fret, a Fmaj13, making chordal improvisation straightforward and harmonically consistent. The prominent G major triad (G-B-D) within the tuning also means that fingerings that emphasize these strings will naturally sound like G major or G-based chords. This tuning invites exploration of both powerful low-end riffs and soaring melodic lines, providing a versatile palette for creative expression.

The open strings for this tuning are as follows (from lowest to highest):

• String 7: C2 (Low C)
• String 6: G2
• String 5: D3
• String 4: G3
• String 3: B3
• String 2: D4
• String 1: E4 (High E)

How to Tune Your Guitar:

To achieve the "Open G/C add6" tuning, you will need to adjust your 7-string guitar from a standard tuning (assuming B E A D G B E, low to high) as follows. Please exercise caution when tuning, especially with significant pitch changes, and consider a different string gauge for movements exceeding 4 semitones.

• String 7 (Low B): Tune up 1 semitones from B1 to C2. (This is a manageable change.)
• String 6 (E): Tune up 3 semitones from E2 to G2. (Take care with this change, monitor string tension.)
• String 5 (A): Tune up 5 semitones from A2 to D3. (Warning: This is a significant change. A different string gauge is strongly advised to prevent string breakage and neck damage.)
• String 4 (D): Tune up 5 semitones from D3 to G3. (Warning: This is a significant change. A different string gauge is strongly advised to prevent string breakage and neck damage.)
• String 3 (G): Tune up 4 semitones from G3 to B3. (Warning: This is a substantial change. Consider a different string gauge to prevent string breakage and neck damage.)
• String 2 (B): Tune up 3 semitones from B3 to D4. (Take care with this change, monitor string tension.)
• String 1 (High E): Keep as is; no change (0 semitones) from E4.