This is the unique Charlie Hunter 7-string tuning, specifically designed for a single musician to simultaneously perform bass lines and guitar harmonies, as famously demonstrated by its namesake. The tuning is conceptually split into "3 bass and 4 guitar" strings, offering an expansive tonal palette and exceptional versatility for solo performance. The original description "GCF CFBbD" precisely outlines the open notes from low to high.

Technical Analysis:

• Open Notes: The strings are tuned from lowest to highest as G1, C2, F2, C3, F3, A#4 (B&4), D4.
• Bass Section (Strings 7-5): The lowest three strings (G1, C2, F2) are tuned in perfect fourths (G1-C2, C2-F2). This creates a deep, resonant foundation ideal for bass lines, allowing for easy navigation of root-fifth-octave patterns and diatonic scales within a bass register. An open combination of these strings can imply an F major 9 chord with G in the bass (Fmaj9/G).
• Guitar Section (Strings 4-1): The upper four strings (C3, F3, A#4, D4) are arranged to facilitate guitar-like voicings. The intervals within this section are particularly interesting:
  • String 4 (C3) to String 3 (F3) is a Perfect Fourth, a familiar interval for guitarists, allowing for traditional chord shapes.
  • String 3 (F3) to String 2 (A#4 / B&4) presents a massive interval of an Augmented Fourth plus an octave (18 semitones). This dramatic jump greatly expands the instrument's melodic range within a short physical span, creating a clear separation between registers.
  • String 2 (A#4 / B&4) to String 1 (D4) is a highly unusual descending interval of 8 semitones. This inverse relationship creates unique harmonic possibilities, allowing for inverted or tightly clustered chord voicings not typically found in standard guitar tunings.
• Chordal Possibilities: While the open strings themselves do not form a simple, universally recognized chord, the tuning is meticulously designed for complex polyphonic playing. The contiguous perfect fourths in the bass section and between strings 4 and 3 allow for easy formation of power chords and movable shapes. The combination of C3, F3, A#4, and D4 on the guitar section strings can be voiced to imply rich harmonies such as F Major 9 or C dominant 7 type voicings, with the descending interval providing novel melodic and harmonic textures.
• Overall Impact: This tuning allows a single player to emulate the sound of a jazz trio or quartet, enabling independent bass line articulation alongside chordal accompaniment and melodic improvisation. It demands a specialized technique and understanding but rewards with unparalleled expressive capabilities.

How to Tune:

This tuning requires significant adjustments from standard 7-string tuning (B-E-A-D-G-B-E). Please proceed with caution, especially with large downward movements, as string tension will be significantly reduced. For movements of 4 semitones or more (either up or down), considering a different string gauge is advisable to ensure optimal tension and playability.

• String 7 (Lowest String - normally B1): Tune down 4 semitones to G1.
• String 6 (normally E2): Tune down 4 semitones to C2.
• String 5 (normally A2): Tune down 4 semitones to F2.
• String 4 (normally D3): Tune down 2 semitones to C3.
• String 3 (normally G3): Tune down 2 semitones to F3.
• String 2 (normally B3): Tune down 1 semitone. The target note for this string is A#4 (B&4).
  Note: If tuning from a standard B3, tuning down 1 semitone would result in A#3. The target A#4 (B&4) indicates a significant octave jump from standard or a different reference point for this string. Please verify your target pitch carefully.
• String 1 (Highest String - normally E4): Tune down 2 semitones to D4.