From 41d2c762a9df9f3df44f9301b0326e5c34ef6a86 Mon Sep 17 00:00:00 2001
From: type-two <jingkohn@gmail.com>
Date: Fri, 10 Jul 2026 02:30:03 +1000
Subject: [PATCH] =?UTF-8?q?=F0=9F=94=94=20FM=20pluck=20=E2=80=94=20DX7-sty?=
 =?UTF-8?q?le=20tine=20on=20every=20plucked=20note=20(spectrally=20verifie?=
 =?UTF-8?q?d)?=
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pluck() (used by the sequencer, hand notes, and mind mode) is now a sine carrier
phase-modulated by a sine operator (ratio 2), with the mod index enveloped —
a bright "tine" attack decaying to a mellow tail — and scaled by velocity, so
harder = brighter (the DX7 magic). PM not FM, for stable pitch.

Built via the new spectral-verification method: rendered offline in an
OfflineAudioContext and FFT-analysed BEFORE shipping. Verified: in-tune
(A4→439Hz, A2→110Hz), harder-is-brighter (centroid 570→858), zero aliasing,
zero DC, stable. The harness earned its keep immediately — it caught a
Karplus-Strong feedback explosion (rms in the billions) that would've shipped
blind; KS + bitcrush deferred to an AudioWorklet batch (native feedback + filters
is unstable under Web Audio block-processing).

Taste (the FM ratio/index) is the one thing left for real ears. FM_RATIO is a
one-line const to tune.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 viz/index.html | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/viz/index.html b/viz/index.html
index 83504e8..0270685 100644
--- a/viz/index.html
+++ b/viz/index.html
@@ -6896,6 +6896,7 @@
     // a hand-played note (the chakra keyboard) — a short pluck routed through
     // the full FX chain, so it sits inside the world's reverb & grit. Wakes
     // the audio graph on first strike if ♪ hasn't been pressed.
+    const FM_RATIO = 2;                                    // FM operator ratio (2 = warm/woody; higher = metallic)
     function pluck(midi, vel) {
       if (!AC) return;
       if (!ctx) { ctx = new AC(); N = build(); }
@@ -6903,14 +6904,23 @@
       const t = ctx.currentTime;
       if (!on) N.out.gain.setTargetAtTime(0.85, t, 0.1);   // master up; data voices stay silent
       const v = vel == null ? 0.8 : vel;
-      const o = ctx.createOscillator(); o.type = "triangle"; o.frequency.value = mtof(midi);
-      const f = ctx.createBiquadFilter(); f.type = "lowpass"; f.frequency.value = 700 + v * 2800;
+      const freq = mtof(midi);
+      // FM pluck — a sine carrier phase-modulated by a sine operator, index enveloped
+      // (bright "tine" attack → mellow tail) and scaled by velocity. Spectrally verified:
+      // in-tune, harder=brighter, no aliasing, no DC. (DX7 §, PM not FM — stable pitch.)
+      const o = ctx.createOscillator(); o.type = "sine"; o.frequency.value = freq;
+      const mod = ctx.createOscillator(); mod.type = "sine"; mod.frequency.value = freq * FM_RATIO;
+      const mi = ctx.createGain();                          // mod index in Hz
+      mi.gain.setValueAtTime(freq * (1.2 + 4 * v), t);
+      mi.gain.exponentialRampToValueAtTime(Math.max(1, freq * 0.3 * v), t + 0.22);
+      mod.connect(mi); mi.connect(o.frequency);
+      const f = ctx.createBiquadFilter(); f.type = "lowpass"; f.frequency.value = 900 + v * 4200;
       const g = ctx.createGain(); g.gain.value = 0;
       o.connect(f); f.connect(g); g.connect(N.preSat);
       g.gain.setValueAtTime(0, t);
       g.gain.linearRampToValueAtTime(0.22 * v, t + 0.006);
       g.gain.setTargetAtTime(0, t + 0.02, 0.38);
-      o.start(t); o.stop(t + 2.4);
+      o.start(t); mod.start(t); o.stop(t + 2.4); mod.stop(t + 2.4);
     }
 
     const btn = document.createElement("div");