This is an highly distinctive and complex tuning for the Guitar, blending a robust low end with a remarkably bright and elevated middle register.

Originally referred to as "Lower Four", this tuning aims to simplify the formation of certain chords on the lower strings, specifically Major, Major 7th, Minor 7th, 6th, and 7th chords. The open string notes are D2-A2-C#4-F#4-B3-E4, from lowest to highest.

Technical Analysis

• Dropped D Bass: The lowest string is tuned down a full step from standard E to D2, providing a deep, resonant foundation characteristic of 'Drop D' tunings. The 5th string remains at A2, creating a perfect fifth interval (D-A) on the bottom, which is excellent for power chords and open D tonalities.
• High Register Middle Strings: Strings 4 and 3 are tuned to C#4 and F#4 respectively. This is a crucial and highly unusual aspect of this tuning. Compared to standard tuning (D3 and G3), these notes represent not only a semitone drop but also an octave increase in pitch. This will result in an exceptionally bright, almost mandolin-like or banjo-like quality for these strings, and will require significantly lighter gauge strings for the 4th and 3rd positions to achieve these pitches safely without excessive tension or breakage.
• Standard Treble: The 2nd (B3) and 1st (E4) strings remain at their standard pitches, providing familiar high-end voicing.

Open Chords and Intervals

• Lower String Chords: The D2-A2-C#4-F#4 sequence on the lower four strings readily forms a D Major 7th chord (D-A-C#-F#). This immediately makes a rich Dmaj7 voicing available with open strings, supporting the tuning's stated goal for easy Maj, Maj7, m7, 6, and 7 chords (by fretting the A string or adding other notes).
• Upper String Intervals: The original description suggests the "top four strings are evenly spaced (all perfect fourths)". However, a closer look at the actual notes (C#4-F#4-B3-E4) reveals the following intervals:
  • C#4 to F#4 is a Perfect Fourth (+5 semitones).
  • F#4 to B3 is a Perfect Fifth Down (-7 semitones).
  • B3 to E4 is a Perfect Fourth (+5 semitones).

  While two pairs are indeed perfect fourths, the F#4 to B3 interval is a perfect fifth down. This creates a unique melodic and harmonic landscape rather than a consistently "all perfect fourths" pattern, offering diverse possibilities for improvisation but perhaps requiring a different approach than a pure all-fourths tuning.

How to Tune (From Standard EADGBe)

• 6th String (Low E to D2): Tune down 2 semitones to D2. Caution: Ensure your string gauge can handle potential tension changes. Tuning down 2 semitones is generally safe for standard strings.
• 5th String (A to A2): Keep as is; no change (0 semitones) to A2.
• 4th String (D to C#4): Tune down 1 semitone to C#4. Extreme Caution: While the relative movement described is 'down 1 semitone', if tuning from a standard D3, reaching C#4 implies tuning up significantly more than 4 semitones (an octave higher than C#3). This necessitates a much thinner string gauge than typically used for the 4th string to prevent breakage and excessive tension.
• 3rd String (G to F#4): Tune down 1 semitone to F#4. Extreme Caution: Similarly, while the relative movement described is 'down 1 semitone', if tuning from a standard G3, reaching F#4 implies tuning up significantly more than 4 semitones (an octave higher than F#3). A significantly lighter gauge string will be essential for safety and playability.
• 2nd String (B to B3): Keep as is; no change (0 semitones) to B3.
• 1st String (High E to E4): Keep as is; no change (0 semitones) to E4.

This tuning is highly experimental due to the extreme pitch changes implied for the 3rd and 4th strings if starting from standard gauges. Consider consulting a luthier for string gauge recommendations to prevent damage to your instrument.