Remix · Impressionist organum in a symmetrical tuning
La Cathédrale Engloutie — reimagined in All Fifths
There's no original guitar tuning to be faithful to — this is solo piano music, written years before anyone would think to play it on guitar at all. But the pairing isn't arbitrary, same as the Giant Steps and Con Alma pages on this site: the piece opens on bare open fifths meant to sound like distant bells, builds its climax from block chords moving in parallel, and even has a passage of pure "chordal planing" — parallel dominant 7th chords sliding along the scale, quality untouched by function. All Fifths tuning, where every string sits a perfect 5th from the next, is the one guitar setup where that logic is already built into the instrument.
This is the least "chord chart" piece on this site — there's no lead sheet for a Debussy prélude, because it was never meant to reduce to one. What follows is a real structural reduction of four specific, well-documented passages: the bell-like opening, the fortissimo "organ" climax, a brief pivot, and the parallel-dominant passage near the end. Simplified down to guitar-shaped chords, but every shape below is grounded in the piece's actual, published harmonic analysis — not a guess at a mood.
Opening · "Profondément calme"
Bare fifths, rising, like bells across water
The famous opening: parallel open fifths and octaves, rising through the G major pentatonic collection (G–A–B–D–E) — no thirds anywhere, which is exactly why it sounds ancient rather than tonal. Stacked in fifths, that same pentatonic scale reorders into G–D–A–E–B, a chain where every neighbor really is a perfect 5th apart.
The opening's rising open fifths, voiced in All Fifths tuning.
Remix with Open—ShapeMeasures 28–41 · "Sonore sans dureté"
The organ in full voice
The climax: the marking literally calls for the sound of a grand organ, fortissimo, thick block chords in both hands. It's built around C major — the most tonal-sounding passage in the entire piece — with a real C Mixolydian inflection (a ♭VII chord) coloring the cascade.
The fortissimo climax, block major triads in All Fifths.
Remix with Open—ShapeMeasures 63 onward
Chordal planing — parallel dominant 7ths
The single most-cited technical moment in the whole prelude: a run of dominant 7th chords whose roots simply follow the C major scale while every chord keeps the same dominant quality, regardless of what would actually be "correct" at that scale degree. It's non-functional harmony reduced to a rule you could teach in one sentence — and it's exactly the sound a guitar built on stacked fifths falls into naturally.
The parallel dominant-7th planing passage, in All Fifths.
Remix with Open—ShapeMeasures 84–89 · Coda
The same bells, sinking back under the water
Debussy marks the coda "comme un écho de la phrase entendue précédemment" — like an echo of the phrase heard before. It's not new material: the piece just dissolves back into the exact same open fifths it opened on, now quiet and low, the cathedral sinking back beneath the surface. Same shapes as the opening above, played back one more time to close the piece where it started.
This is a structural reduction of a through-composed piano piece, not a lead sheet — no chord chart for this piece exists anywhere. Every chord shown is grounded in the piece's published harmonic analysis and verified against the app's own voicing engine in the real All Fifths tuning, no Pro unlock needed.