Pedals / Organ stop voicing

Organ Donor

Organ stop voicing · play-tested

seth — fish

seth@ninevolt:~$

Organ Donor in the Ninevolt TUI — Click to enlarge

Knobs

In the TUI each knob runs from low (left / 0%) to high (right / 100%). Start near noon, then nudge while you play.

Stops

Chooses which organ-style voice combination is active (sweep to hear different stops).

Turn up Moves through brighter / higher stop combinations toward the top of the range.
Turn down Toward quieter or darker stop selections at the bottom (including near-silence at zero).

Mix

Organ voice versus dry guitar.

Turn up More organ character.
Turn down More dry guitar.

Swell

Expression-like loudness of the organ voice.

Turn up Louder organ swell.
Turn down Softer organ under the guitar.

Inspired by

Not a commercial stompbox — Ninevolt’s pipe-organ pitch-down voice: delay-line read pointer shifts pitch in whole semitones (organ stop footages), a swell shoe blooms the attack, and a fixed chest tap adds low-mid body. Built for the Cathedral Crunch profile (organ-cathedral-crunch.yaml) — organ into RAT, not a Leslie rotor sim.

Stop names on presets (4′ Principal, 16′ Gedackt, 64′ Bourdon) follow pipe-organ rank naming — each preset is one semitone step down through a full octave.

Pitch-shift family: see Pure Octave (parallel sub/oct layers) and Bend Box (Whammy-style treadle bends). Organ Donor is a single pitched-down organ line with swell.

Signal path

Step	What it does
Delay line write	Sample stored in ~250 ms ring buffer.
Variable-speed read + reset crossfade	Stops → 0–12 semitones down (`2^(−n/12)` read ratio); linear interp; equal-power crossfade (~28 ms) when read gap exceeds latency + grain (~72 ms).
Chest resonance tap	Fixed ~9 ms tap behind read head; ~14% body mix, scaled by swell gain.
2-pole warmth LP	Cutoff opens as swell shoe opens — dark attack, brighter sustain.
Swell shoe envelope	Swell follows rectified peaks (5 ms–3.2 s attack, 30 ms–1.4 s release); gates wet level for key-down bloom.
Dry/wet Mix	Mix blends dry input with swelled organ line.
Bypass engage crossfade	~5 ms equal-power crossfade on stomp (dry path still passes `tanh`).
Soft clip tanh	Limits peaks on the final blend.
Output	Mono organ voice to the chain.

How we modeled it

Monophonic pitch-down shifter: write at unity, read at current_ratio < 1. Ratio glides (~6% per sample) when Stops changes. Rare read-pointer resets avoid unbounded drift without audible warble (see tests). Swell at ~0 passes wet at unity gain; high Swell slows attack dramatically.

Simplifications

- Mono output — no Leslie stereo rotor - Pitch down only (no octave up, no parallel sub+oct like Pocket POG) - Monophonic delay-line shifter — no polyphonic tracking - Stop names ≠ strict pipe-length physics — semitone steps with organ labels