The Open A add4 tuning presents a rich, resonant soundscape, offering unique harmonic possibilities. As described, it stands "along the lines of open C," suggesting a similar versatility and chordal exploration potential. The prominent inclusion of D notes, specifically "double fourths (D)," indeed makes this tuning feel as much like an Open D tuning as it does an Open A, providing a powerful lower register. The "major 7th on D" refers to the C# note on the highest string, which functions as a pleasing major seventh for any D-rooted harmony, while simultaneously acting as the major third for the prevalent A root.

Technical Analysis

This tuning, from lowest to highest string, is configured as A1-D2-A2-D3-A3-C#5. The open strings collectively form a complex voicing. The fundamental notes are A (root), D (perfect fourth), and C# (major third). With A as the root, the tuning can be interpreted as an A major chord with an added perfect fourth (D) and multiple octaves of A and D. This creates a full, almost drone-like quality on the lower strings, punctuated by the bright C# on the first string. The C#5 on the highest string provides a distinct, exceptionally high pitch which offers a cutting edge to the overall sound, pushing the upper register significantly. The abundance of A and D notes across the strings (A-D-A-D-A-C#) makes this tuning particularly resonant for A major, A sus4, D major, and D major 7 harmonies.

Open Chords and Playability

Strumming the open strings (A-D-A-D-A-C#) yields a powerful A major chord, heavily colored by the D natural (the perfect fourth). This creates an expansive, full sound ideal for blues, folk, and rock music.
The repeating intervals (A-D-A-D-A) across the lower five strings mean that simple barre chords become very effective. Sliding a finger across a single fret will produce musically useful chords:

• Fretting all strings at the 2nd fret would yield a B major sound (B-E-B-E-B-D#).
• At the 5th fret, a D major sound (D-G-D-G-D-F#) would emerge, demonstrating the D-centric aspect mentioned in the original description.
• This structure makes it exceptionally well-suited for slide guitar playing, allowing for fluid melodic and chordal movements with minimal effort.
• Fingerstyle players can find interesting arpeggios and voicings, leveraging the open perfect fourths and octaves.

How to Tune

To achieve this Open A add4 tuning from standard EADGBe, follow these steps. Please note that significant downward tuning (more than 4 semitones) might benefit from a lighter gauge string set to maintain tension and intonation, though the provided tuning is achievable with standard gauges if careful.

• String 6 (Low E): Tune down 7 semitones to A1.
• String 5 (A): Tune down 7 semitones to D2.
• String 4 (D): Tune down 5 semitones to A2.
• String 3 (G): Tune down 5 semitones to D3.
• String 2 (B): Tune down 2 semitones to A3.
• String 1 (High E): Tune down 3 semitones to C#4.