This tuning, aptly named "Modal C 9", is described as a "Cross-modal version of Mark Holcomb's Open Cadd9 tuning." However, its open string notes reveal a much more complex and dissonant harmonic landscape than a typical Cadd9. Rather than the bright, expansive sound of a Cadd9, this tuning delves into a darker, more aggressive tonal territory, characteristic of modern progressive metal and djent styles championed by artists like Mark Holcomb.

Technical Breakdown:

• The open strings are tuned to: C2 G2 C3 D#4 G3 C#5.
• Analyzing the intervals from the lowest C (C2):
  • C2 (Root)
  • G2 (Perfect 5th)
  • C3 (Octave)
  • D#4 (Minor 3rd/Eb from C, but high octave)
  • G3 (Octave Perfect 5th)
  • C#5 (Minor 2nd/Augmented Prime from C)
• The most striking feature is the simultaneous presence of C and C# (enharmonically Db) across the open strings. This creates a highly dissonant minor second interval, which is the hallmark of "cross-modal" and can be used to generate extreme tension, harshness, or for specific atonal/bitonal effects.
• The inclusion of D# (Eb) provides a minor third, suggesting a C minor tonality (C-Eb-G) if the C# is omitted or used carefully. However, the C# fundamentally alters this, moving it away from conventional minor harmony into a more experimental space.

Open Chords & Playability:

• Power Chords: The lowest three strings (C2 G2 C3) form a strong C5 power chord, making it excellent for heavy, riff-based playing. Barring these three strings at any fret will easily yield power chords.
• Dissonant Voicings: Strumming all six open strings will produce a highly dissonant chord due to the C/C# clash. This suggests that the tuning is likely intended for selective picking, palm-muted chugs, or creating specific, jarring harmonic textures rather than broad, open strumming.
• Minor Flavors: By carefully avoiding or muting the high C# string, you can emphasize a C minor tonality using the C-G-C-D#-G strings, opening up avenues for dark, melancholic chord progressions and riffs.
• Extended Intervals: The two Gs (G2, G3) and two Cs (C2, C3) at different octaves provide a thick, resonant foundation for single-note lines and riffs, adding depth to the sound.
• This tuning is ideal for guitarists exploring modern, aggressive, and experimental genres where conventional harmony is often set aside in favor of tension, impact, and unique sonic landscapes.

How to Tune:

Standard EADGBe tuning is the assumed starting point for these adjustments. Be mindful of string tension, especially with large tuning changes, and always use a reliable tuner.

• String 6 (Low E to C2): Tune down 4 semitones. (From a standard E2, this movement will bring you to C2).
• String 5 (A to G2): Tune down 2 semitones. (From a standard A2, this movement will bring you to G2).
• String 4 (D to C3): Tune down 2 semitones. (From a standard D3, this movement will bring you to C3).
• String 3 (G to D#4): Tune down 4 semitones. (From a standard G3, this movement would typically result in D#3. However, the target note for this tuning is D#4. Consider if your guitar or string gauge is intended for this octave jump if starting from standard G3).
• String 2 (B to G3): Tune down 4 semitones. (From a standard B3, this movement will bring you to G3).
• String 1 (High E to C#5): Tune down 3 semitones. (From a standard E4, this movement would typically result in C#4. However, the target note for this tuning is C#5. Consider if your guitar or string gauge is intended for this octave jump if starting from standard E4).

Important Note on String Gauge: Adjusting strings by more than 4 semitones (either up or down, as seen with String 6, String 3, String 2, and String 1) can significantly alter string tension. For optimal playability, intonation, and to prevent potential damage, it is highly recommended to consider using a different string gauge specifically suited for these lower or higher tunings, especially if the target notes involve an octave shift from standard.