Synth v2: modular pro layout, HOLD latching pads, fuller voice engine

- Modular hardware-style panel: System / Oscillator / Filter / Envelope
  / LFO / Drive / Echo / Output / Keyboard sections with labeled frames
- HOLD switch: pads become latching toggles (switching pads retunes the
  held note, unlatching or disabling HOLD releases it)
- Fuller Web Audio voice: waveshaper drive, full ADSR, feedback delay
  (time/feedback/mix), LFO target switch (cutoff or pitch via detune),
  octave/detune/glide with live retuning of held notes
- More of the library in service: MetalKnob (drive, with value bubble),
  VintageKnob (echo time), horizontal LEDFader (echo mix), XYPad
  two-way-linked with the cutoff/res knobs (exponential x-axis mapping),
  SegmentDisplay live frequency readout, 4 preset buttons that glide
  every knob via animateChanges
- Disambiguated synth aria-labels from gallery demos; octave readout
  fixed via decimals/format
- SteppedKnob now honors the format prop for numeric readouts

apps/docs/src/sections/Synth.tsx

@@ -3,12 +3,17 @@ import {
   AlphaDisplay,
   Fader,
   FlatKnob,
+  LEDFader,
   LEDKnob,
+  MetalKnob,
   Meter,
   NeonKnob,
   PushButton,
   RubberKnob,
+  SegmentDisplay,
   SteppedKnob,
+  VintageKnob,
+  XYPad,
   logTaper,
   powTaper,
 } from 'dreamknob';
@@ -28,55 +33,122 @@ const WAVES: OscillatorType[] = ['sawtooth', 'square', 'triangle'];
 
 interface Params {
   wave: number;
+  octave: number; // -2..+2 (SteppedKnob index handled via min/max)
+  detune: number; // cents
+  glide: number; // ms
   cutoff: number;
   res: number;
-  attack: number; // ms
+  attack: number;
-  release: number; // ms
+  decay: number;
+  sustain: number; // 0..100 %
+  release: number;
   lfoRate: number;
   lfoDepth: number;
+  lfoTarget: number; // 0 = cutoff, 1 = pitch
+  drive: number; // 0..100
+  delayTime: number; // ms
+  feedback: number; // 0..90 %
+  delayMix: number; // 0..100 %
   master: number; // dB
 }
 
+const INIT: Params = {
+  wave: 0, octave: 0, detune: 0, glide: 30,
+  cutoff: 1200, res: 6,
+  attack: 8, decay: 180, sustain: 65, release: 300,
+  lfoRate: 4, lfoDepth: 12, lfoTarget: 0,
+  drive: 12, delayTime: 320, feedback: 35, delayMix: 20,
+  master: -12,
+};
+
+const PRESETS: { name: string; params: Partial<Params> }[] = [
+  { name: 'INIT', params: INIT },
+  {
+    name: 'WARM PAD',
+    params: { wave: 2, cutoff: 640, res: 3, attack: 420, decay: 600, sustain: 80, release: 900, lfoRate: 0.6, lfoDepth: 8, lfoTarget: 0, drive: 4, delayTime: 460, feedback: 45, delayMix: 38, glide: 120 },
+  },
+  {
+    name: 'ACID 303',
+    params: { wave: 0, cutoff: 900, res: 18, attack: 2, decay: 140, sustain: 20, release: 90, lfoRate: 6, lfoDepth: 0, lfoTarget: 0, drive: 55, delayTime: 180, feedback: 30, delayMix: 18, glide: 60 },
+  },
+  {
+    name: 'WOBBLE',
+    params: { wave: 1, cutoff: 500, res: 12, attack: 10, decay: 300, sustain: 90, release: 200, lfoRate: 4.5, lfoDepth: 70, lfoTarget: 0, drive: 30, delayTime: 260, feedback: 25, delayMix: 22, glide: 0 },
+  },
+];
+
 interface Engine {
   ctx: AudioContext;
   osc: OscillatorNode;
+  shaper: WaveShaperNode;
   env: GainNode;
   filter: BiquadFilterNode;
   lfo: OscillatorNode;
   lfoGain: GainNode;
+  dry: GainNode;
+  wet: GainNode;
+  delay: DelayNode;
+  fb: GainNode;
   master: GainNode;
   analyser: AnalyserNode;
 }
 
+const driveCurve = (amount: number) => {
+  const k = amount * 0.6;
+  const n = 256;
+  const curve = new Float32Array(n);
+  for (let i = 0; i < n; i++) {
+    const x = (i * 2) / (n - 1) - 1;
+    curve[i] = ((1 + k / 20) * x) / (1 + (k / 20) * Math.abs(x));
+  }
+  return curve;
+};
+
+// XY pad x-axis (0..100) <-> cutoff Hz, exponential so travel feels musical.
+const CUT_MIN = 60;
+const CUT_MAX = 12000;
+const xToCut = (x: number) => CUT_MIN * Math.pow(CUT_MAX / CUT_MIN, x / 100);
+const cutToX = (c: number) => (Math.log(c / CUT_MIN) / Math.log(CUT_MAX / CUT_MIN)) * 100;
+
+const Module: React.FC<{ title: string; children: React.ReactNode }> = ({ title, children }) => (
+  <div className="synth-module">
+    <span className="module-title">{title}</span>
+    <div className="module-body">{children}</div>
+  </div>
+);
+
 export const Synth: React.FC = () => {
   const [powered, setPowered] = React.useState(false);
-  const [params, setParams] = React.useState<Params>({
+  const [hold, setHold] = React.useState(false);
-    wave: 0,
+  const [preset, setPreset] = React.useState(0);
-    cutoff: 1200,
+  const [params, setParams] = React.useState<Params>(INIT);
-    res: 6,
-    attack: 12,
-    release: 260,
-    lfoRate: 4,
-    lfoDepth: 15,
-    master: -12,
-  });
   const [note, setNote] = React.useState<string | null>(null);
   const [meterDb, setMeterDb] = React.useState(-60);
   const engine = React.useRef<Engine | null>(null);
+  const baseFreq = React.useRef<number | null>(null);
   const paramsRef = React.useRef(params);
   paramsRef.current = params;
 
   const set = <K extends keyof Params>(key: K, v: Params[K]) =>
     setParams(p => ({ ...p, [key]: v }));
 
+  const loadPreset = (i: number) => {
+    setPreset(i);
+    setParams(p => ({ ...p, ...PRESETS[i].params }));
+  };
+
   // Build / tear down the audio graph with power.
   React.useEffect(() => {
     if (!powered) return;
     const ctx = new AudioContext();
     const p = paramsRef.current;
+
     const osc = ctx.createOscillator();
     osc.type = WAVES[p.wave];
     osc.frequency.value = 220;
+    const shaper = ctx.createWaveShaper();
+    shaper.curve = driveCurve(p.drive);
+    shaper.oversample = '2x';
     const env = ctx.createGain();
     env.gain.value = 0;
     const filter = ctx.createBiquadFilter();
@@ -86,24 +158,37 @@ export const Synth: React.FC = () => {
     const lfo = ctx.createOscillator();
     lfo.frequency.value = p.lfoRate;
     const lfoGain = ctx.createGain();
-    lfoGain.gain.value = p.lfoDepth * 12; // depth% -> Hz swing on the cutoff
+    const dry = ctx.createGain();
+    const wet = ctx.createGain();
+    const delay = ctx.createDelay(2);
+    delay.delayTime.value = p.delayTime / 1000;
+    const fb = ctx.createGain();
+    fb.gain.value = p.feedback / 100;
+    dry.gain.value = 1 - (p.delayMix / 100) * 0.7;
+    wet.gain.value = p.delayMix / 100;
     const master = ctx.createGain();
     master.gain.value = Math.pow(10, p.master / 20);
     const analyser = ctx.createAnalyser();
     analyser.fftSize = 1024;
 
-    osc.connect(env);
+    osc.connect(shaper);
+    shaper.connect(env);
     env.connect(filter);
-    filter.connect(master);
+    filter.connect(dry);
+    filter.connect(delay);
+    delay.connect(fb);
+    fb.connect(delay);
+    delay.connect(wet);
+    dry.connect(master);
+    wet.connect(master);
     master.connect(analyser);
     analyser.connect(ctx.destination);
     lfo.connect(lfoGain);
-    lfoGain.connect(filter.frequency);
+    // Initial LFO routing happens in the params effect below.
     osc.start();
     lfo.start();
-    engine.current = { ctx, osc, env, filter, lfo, lfoGain, master, analyser };
+    engine.current = { ctx, osc, shaper, env, filter, lfo, lfoGain, dry, wet, delay, fb, master, analyser };
 
-    // Meter: RMS of the output, throttled to ~25 fps.
     const buf = new Float32Array(analyser.fftSize);
     let raf = 0;
     let last = 0;
@@ -122,6 +207,7 @@ export const Synth: React.FC = () => {
     return () => {
       cancelAnimationFrame(raf);
       engine.current = null;
+      baseFreq.current = null;
       void ctx.close();
       setMeterDb(-60);
       setNote(null);
@@ -129,26 +215,60 @@ export const Synth: React.FC = () => {
   }, [powered]);
 
   // Live parameter updates.
+  const lfoTargetRef = React.useRef(-1);
   React.useEffect(() => {
     const e = engine.current;
     if (!e) return;
     const t = e.ctx.currentTime;
     e.osc.type = WAVES[params.wave];
+    e.shaper.curve = driveCurve(params.drive);
     e.filter.frequency.setTargetAtTime(params.cutoff, t, 0.015);
     e.filter.Q.setTargetAtTime(params.res, t, 0.015);
     e.lfo.frequency.setTargetAtTime(params.lfoRate, t, 0.015);
-    e.lfoGain.gain.setTargetAtTime(params.lfoDepth * 12, t, 0.015);
+    e.delay.delayTime.setTargetAtTime(params.delayTime / 1000, t, 0.03);
+    e.fb.gain.setTargetAtTime(Math.min(params.feedback, 90) / 100, t, 0.015);
+    e.dry.gain.setTargetAtTime(1 - (params.delayMix / 100) * 0.7, t, 0.015);
+    e.wet.gain.setTargetAtTime(params.delayMix / 100, t, 0.015);
     e.master.gain.setTargetAtTime(Math.pow(10, params.master / 20), t, 0.015);
-  }, [params]);
+    // LFO target: cutoff (Hz swing) or pitch (cents on detune).
+    if (lfoTargetRef.current !== params.lfoTarget) {
+      try {
+        e.lfoGain.disconnect();
+      } catch {
+        /* not connected yet */
+      }
+      if (params.lfoTarget === 0) e.lfoGain.connect(e.filter.frequency);
+      else e.lfoGain.connect(e.osc.detune);
+      lfoTargetRef.current = params.lfoTarget;
+    }
+    const depth = params.lfoTarget === 0 ? params.lfoDepth * 14 : params.lfoDepth * 0.6;
+    e.lfoGain.gain.setTargetAtTime(depth, t, 0.015);
+    // Retune a held note when octave/detune change.
+    if (baseFreq.current !== null) applyPitch(baseFreq.current);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [params, powered]);
+
+  const applyPitch = (base: number) => {
+    const e = engine.current;
+    if (!e) return;
+    const p = paramsRef.current;
+    const freq = base * Math.pow(2, p.octave) * Math.pow(2, p.detune / 1200);
+    const tc = Math.max(0.002, p.glide / 1000 / 3);
+    e.osc.frequency.setTargetAtTime(freq, e.ctx.currentTime, tc);
+  };
 
   const noteOn = (freq: number, name: string) => {
     const e = engine.current;
     if (!e) return;
+    baseFreq.current = freq;
+    applyPitch(freq);
+    const p = paramsRef.current;
     const t = e.ctx.currentTime;
-    e.osc.frequency.setTargetAtTime(freq, t, 0.002);
+    const g = e.env.gain;
-    e.env.gain.cancelScheduledValues(t);
+    g.cancelScheduledValues(t);
-    e.env.gain.setValueAtTime(e.env.gain.value, t);
+    g.setValueAtTime(g.value, t);
-    e.env.gain.linearRampToValueAtTime(0.5, t + paramsRef.current.attack / 1000);
+    g.linearRampToValueAtTime(0.55, t + p.attack / 1000);
+    g.linearRampToValueAtTime(0.55 * (p.sustain / 100), t + p.attack / 1000 + p.decay / 1000);
     setNote(name);
   };
 
@@ -156,13 +276,27 @@ export const Synth: React.FC = () => {
     const e = engine.current;
     if (!e) return;
     const t = e.ctx.currentTime;
-    e.env.gain.cancelScheduledValues(t);
+    const g = e.env.gain;
-    e.env.gain.setValueAtTime(e.env.gain.value, t);
+    g.cancelScheduledValues(t);
-    e.env.gain.linearRampToValueAtTime(0, t + paramsRef.current.release / 1000);
+    g.setValueAtTime(g.value, t);
+    g.linearRampToValueAtTime(0, t + paramsRef.current.release / 1000);
+    baseFreq.current = null;
     setNote(null);
   };
 
+  // Turning HOLD off releases a latched note.
+  React.useEffect(() => {
+    if (!hold && note) noteOff();
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [hold]);
+
   const hz = (v: number) => (v >= 1000 ? `${(v / 1000).toFixed(1)}k` : `${Math.round(v)}`);
+  const shownFreq = note
+    ? (NOTES.find(n => n.name === note)?.freq ?? 0) *
+      Math.pow(2, params.octave) *
+      Math.pow(2, params.detune / 1200)
+    : 0;
+  const anim = { animateChanges: { duration: 300 } as const };
 
   return (
     <section className="block" id="synth">
@@ -170,158 +304,356 @@ export const Synth: React.FC = () => {
         <div className="section-kicker">Play it</div>
         <h2 className="section-title">A real synth, all dreamknob controls</h2>
         <p className="section-sub">
-          Every control drives an actual Web Audio graph — power it on, hold the pads, and
+          Every control drives an actual Web Audio graph. Power on, pick a preset (watch
-          sweep the filter. The meter reads the analyser; the display shows the note.
+          the knobs glide), hold or latch the pads, and sweep the filter — from the knobs
+          or the XY pad, they're the same parameters.
         </p>
-        <div className="console" style={{ flexDirection: 'column', gap: 22 }}>
+        <div className="console" style={{ flexDirection: 'column', gap: 16 }}>
-          <div style={{ display: 'flex', gap: 26, alignItems: 'center', justifyContent: 'center', flexWrap: 'wrap' }}>
+          <div className="synth-rows">
-            <PushButton
+            <div className="synth-row">
-              pressed={powered}
+              <Module title="System">
-              onChange={setPowered}
+                <PushButton pressed={powered} onChange={setPowered} color="#ff4d6b" size={40} aria-label="Power">
-              color="#ff4d6b"
+                  Power
-              size={40}
+                </PushButton>
-              aria-label="Power"
+                <div style={{ display: 'flex', flexDirection: 'column', gap: 6, alignItems: 'center' }}>
-            >
+                  <AlphaDisplay
-              Power
+                    value={!powered ? 'OFF' : (note ?? PRESETS[preset].name)}
-            </PushButton>
+                    chars={9}
-            <AlphaDisplay
+                    height={16}
-              value={!powered ? 'OFF' : (note ?? 'READY')}
+                    color={powered ? '#3df2ad' : '#3a3f46'}
-              chars={6}
+                  />
-              align="right"
+                  <SegmentDisplay
-              height={18}
+                    value={shownFreq}
-              color={powered ? '#3df2ad' : '#3a3f46'}
+                    digits={5}
-            />
+                    decimals={1}
-            <SteppedKnob
+                    height={11}
-              size={76}
+                    color={note ? '#4cc2ff' : '#2a2f36'}
-              positions={['SAW', 'SQR', 'TRI']}
+                    ghostOpacity={0.12}
-              value={params.wave}
+                  />
-              onChange={v => set('wave', v)}
+                </div>
-              color="#ffd23e"
+                <div style={{ display: 'flex', gap: 6 }}>
-              label="Osc"
+                  {PRESETS.map((p, i) => (
-              aria-label="Oscillator wave"
+                    <PushButton
-            />
+                      key={p.name}
-            <RubberKnob
+                      pressed={preset === i}
-              size={76}
+                      onChange={on => on && loadPreset(i)}
-              min={60}
+                      color="#3df2ad"
-              max={12000}
+                      size={32}
-              taper={logTaper}
+                      aria-label={`Load preset ${p.name}`}
-              decimals={0}
+                    >
-              value={params.cutoff}
+                      {i + 1}
-              onChange={v => set('cutoff', v)}
+                    </PushButton>
-              showValue
+                  ))}
-              format={hz}
+                </div>
-              color="#ff9640"
+              </Module>
-              label="Cutoff"
+
-              aria-label="Filter cutoff"
+              <Module title="Oscillator">
-            />
+                <SteppedKnob
-            <FlatKnob
+                  size={70}
-              size={76}
+                  positions={['SAW', 'SQR', 'TRI']}
-              min={0}
+                  value={params.wave}
-              max={24}
+                  onChange={v => set('wave', v)}
-              step={0.5}
+                  color="#ffd23e"
-              value={params.res}
+                  label="Wave"
-              onChange={v => set('res', v)}
+                  aria-label="Oscillator wave"
-              color="#ff9640"
+                />
-              label="Res"
+                <SteppedKnob
-              aria-label="Filter resonance"
+                  size={70}
-            />
+                  min={-2}
-            <FlatKnob
+                  max={2}
-              size={76}
+                  steps={5}
-              min={1}
+                  decimals={0}
-              max={1000}
+                  value={params.octave}
-              taper={powTaper(2.5)}
+                  onChange={v => set('octave', v)}
-              decimals={0}
+                  color="#ffd23e"
-              value={params.attack}
+                  format={v => (v > 0 ? `+${v}` : `${v}`)}
-              onChange={v => set('attack', v)}
+                  label="Octave"
-              unit="ms"
+                  aria-label="Octave"
-              color="#4cc2ff"
+                />
-              label="Attack"
+                <FlatKnob
-              aria-label="Envelope attack"
+                  size={70}
-            />
+                  min={-100}
-            <FlatKnob
+                  max={100}
-              size={76}
+                  step={1}
-              min={10}
+                  origin={0}
-              max={3000}
+                  detents={[0]}
-              taper={powTaper(2.5)}
+                  arcFrom="center"
-              decimals={0}
+                  value={params.detune}
-              value={params.release}
+                  onChange={v => set('detune', v)}
-              onChange={v => set('release', v)}
+                  color="#ffd23e"
-              unit="ms"
+                  unit="¢"
-              color="#4cc2ff"
+                  label="Detune"
-              label="Release"
+                  aria-label="Detune"
-              aria-label="Envelope release"
+                  {...anim}
-            />
+                />
-            <LEDKnob
+                <FlatKnob
-              size={76}
+                  size={70}
-              min={0.1}
+                  min={0}
-              max={20}
+                  max={500}
-              taper={logTaper}
+                  taper={powTaper(2)}
-              decimals={1}
+                  decimals={0}
-              value={params.lfoRate}
+                  value={params.glide}
-              onChange={v => set('lfoRate', v)}
+                  onChange={v => set('glide', v)}
-              digits={4}
+                  color="#ffd23e"
-              displayDecimals={1}
+                  unit="ms"
-              color="#3df2ad"
+                  label="Glide"
-              label="LFO Hz"
+                  aria-label="Glide"
-              aria-label="LFO rate"
+                  {...anim}
-            />
+                />
-            <NeonKnob
+              </Module>
-              size={76}
+
-              min={0}
+              <Module title="Filter">
-              max={100}
+                <RubberKnob
-              step={1}
+                  size={80}
-              value={params.lfoDepth}
+                  min={CUT_MIN}
-              onChange={v => set('lfoDepth', v)}
+                  max={CUT_MAX}
-              color="#e44cff"
+                  taper={logTaper}
-              label="Depth"
+                  decimals={0}
-              aria-label="LFO depth"
+                  value={params.cutoff}
-            />
+                  onChange={v => set('cutoff', v)}
-            <Fader
+                  showValue
-              length={120}
+                  format={hz}
-              breadth={40}
+                  editable
-              min={-60}
+                  color="#ff9640"
-              max={0}
+                  label="Cutoff"
-              step={0.5}
+                  aria-label="Filter cutoff"
-              value={params.master}
+                  {...anim}
-              onChange={v => set('master', v)}
+                />
-              origin={-60}
+                <FlatKnob
-              editable
+                  size={70}
-              unit=" dB"
+                  min={0}
-              label="Master"
+                  max={24}
-              aria-label="Master volume"
+                  step={0.5}
-            />
+                  value={params.res}
-            <Meter
+                  onChange={v => set('res', v)}
-              value={meterDb}
+                  color="#ff9640"
-              min={-60}
+                  label="Res"
-              max={0}
+                  aria-label="Filter resonance"
-              length={120}
+                  {...anim}
-              zones={[
+                />
-                { upTo: 0.7, color: '#3df2ad' },
+                <XYPad
-                { upTo: 0.9, color: '#ffd23e' },
+                  width={150}
-                { upTo: 1, color: '#ff4d6b' },
+                  height={104}
-              ]}
+                  x={{ min: 0, max: 100, defaultValue: cutToX(INIT.cutoff) }}
-              peakColor="#fff"
+                  y={{ min: 0, max: 24, step: 0.5, defaultValue: INIT.res }}
-              label="Out"
+                  value={{ x: cutToX(params.cutoff), y: params.res }}
-              aria-label="Synth output level"
+                  onChange={v => setParams(p => ({ ...p, cutoff: Math.round(xToCut(v.x)), res: v.y }))}
-            />
+                  formatX={v => hz(xToCut(v))}
-          </div>
+                  formatY={v => v.toFixed(1)}
-          <div style={{ display: 'flex', gap: 8, justifyContent: 'center', flexWrap: 'wrap' }}>
+                  color="#ff9640"
-            {NOTES.map(n => (
+                  grid={4}
-              <PushButton
+                  label="Cut / Res"
-                key={n.name}
+                  aria-label="Filter cutoff and resonance pad"
-                mode="momentary"
+                />
-                onChange={on => (on ? noteOn(n.freq, n.name) : noteOff())}
+              </Module>
-                color="#3df2ad"
+            </div>
-                size={44}
+
-                disabled={!powered}
+            <div className="synth-row">
-                aria-label={`Play ${n.name}`}
+              <Module title="Envelope">
-              >
+                {(
-                {n.name}
+                  [
-              </PushButton>
+                    ['attack', 'Atk', 1, 1000],
-            ))}
+                    ['decay', 'Dec', 1, 2000],
+                    ['sustain', 'Sus', 0, 100],
+                    ['release', 'Rel', 10, 3000],
+                  ] as const
+                ).map(([key, label, min, max]) => (
+                  <FlatKnob
+                    key={key}
+                    size={62}
+                    min={min}
+                    max={max}
+                    taper={key === 'sustain' ? undefined : powTaper(2.2)}
+                    decimals={0}
+                    value={params[key]}
+                    onChange={v => set(key, v)}
+                    color="#4cc2ff"
+                    unit={key === 'sustain' ? '%' : 'ms'}
+                    label={label}
+                    aria-label={`Envelope ${key}`}
+                    {...anim}
+                  />
+                ))}
+              </Module>
+
+              <Module title="LFO">
+                <LEDKnob
+                  size={70}
+                  min={0.1}
+                  max={20}
+                  taper={logTaper}
+                  decimals={1}
+                  value={params.lfoRate}
+                  onChange={v => set('lfoRate', v)}
+                  digits={4}
+                  displayDecimals={1}
+                  color="#3df2ad"
+                  label="Rate"
+                  aria-label="LFO rate"
+                />
+                <NeonKnob
+                  size={70}
+                  min={0}
+                  max={100}
+                  step={1}
+                  value={params.lfoDepth}
+                  onChange={v => set('lfoDepth', v)}
+                  color="#e44cff"
+                  label="Depth"
+                  aria-label="LFO depth"
+                  {...anim}
+                />
+                <SteppedKnob
+                  size={70}
+                  positions={['CUT', 'PIT']}
+                  value={params.lfoTarget}
+                  onChange={v => set('lfoTarget', v)}
+                  color="#e44cff"
+                  label="Target"
+                  aria-label="LFO target"
+                />
+              </Module>
+
+              <Module title="Drive">
+                <MetalKnob
+                  size={80}
+                  tone="dark"
+                  min={0}
+                  max={100}
+                  step={1}
+                  value={params.drive}
+                  onChange={v => set('drive', v)}
+                  color="#ff4d6b"
+                  valueBubble
+                  bubbleFormat={v => `${v} %`}
+                  label="Drive"
+                  aria-label="Drive"
+                  {...anim}
+                />
+              </Module>
+
+              <Module title="Echo">
+                <VintageKnob
+                  size={80}
+                  bodyColor="#26221f"
+                  min={40}
+                  max={1200}
+                  step={10}
+                  value={params.delayTime}
+                  onChange={v => set('delayTime', v)}
+                  color="#ffd23e"
+                  label="Time"
+                  aria-label="Delay time"
+                />
+                <FlatKnob
+                  size={62}
+                  min={0}
+                  max={90}
+                  step={1}
+                  value={params.feedback}
+                  onChange={v => set('feedback', v)}
+                  color="#ffd23e"
+                  unit="%"
+                  label="Fdbk"
+                  aria-label="Delay feedback"
+                  {...anim}
+                />
+                <LEDFader
+                  orientation="horizontal"
+                  length={120}
+                  breadth={26}
+                  min={0}
+                  max={100}
+                  step={1}
+                  value={params.delayMix}
+                  onChange={v => set('delayMix', v)}
+                  color="#ffd23e"
+                  displayDecimals={0}
+                  label="Mix"
+                  aria-label="Delay mix"
+                />
+              </Module>
+
+              <Module title="Output">
+                <Fader
+                  length={120}
+                  breadth={40}
+                  min={-60}
+                  max={0}
+                  step={0.5}
+                  value={params.master}
+                  onChange={v => set('master', v)}
+                  origin={-60}
+                  editable
+                  unit=" dB"
+                  label="Master"
+                  aria-label="Master volume"
+                />
+                <Meter
+                  value={meterDb}
+                  min={-60}
+                  max={0}
+                  length={120}
+                  zones={[
+                    { upTo: 0.7, color: '#3df2ad' },
+                    { upTo: 0.9, color: '#ffd23e' },
+                    { upTo: 1, color: '#ff4d6b' },
+                  ]}
+                  peakColor="#fff"
+                  label="Out"
+                  aria-label="Synth output level"
+                />
+              </Module>
+            </div>
+
+            <div className="synth-row">
+              <Module title="Keyboard">
+                <div className="synth-pads">
+                  <PushButton
+                    pressed={hold}
+                    onChange={setHold}
+                    color="#4cc2ff"
+                    size={40}
+                    disabled={!powered}
+                    aria-label="Hold notes"
+                  >
+                    Hold
+                  </PushButton>
+                  <span style={{ width: 10 }} />
+                  {NOTES.map(n =>
+                    hold ? (
+                      <PushButton
+                        key={n.name}
+                        pressed={note === n.name}
+                        onChange={on => (on ? noteOn(n.freq, n.name) : noteOff())}
+                        color="#3df2ad"
+                        size={44}
+                        disabled={!powered}
+                        aria-label={`Latch ${n.name}`}
+                      >
+                        {n.name}
+                      </PushButton>
+                    ) : (
+                      <PushButton
+                        key={n.name}
+                        mode="momentary"
+                        onChange={on => (on ? noteOn(n.freq, n.name) : noteOff())}
+                        color="#3df2ad"
+                        size={44}
+                        disabled={!powered}
+                        aria-label={`Play ${n.name}`}
+                      >
+                        {n.name}
+                      </PushButton>
+                    ),
+                  )}
+                </div>
+              </Module>
+            </div>
           </div>
           <div className="rack-hint" style={{ marginTop: 0 }}>
-            power on · hold a pad · sweep the cutoff while a note rings
+            power on · try preset 2 and watch the knobs glide · HOLD latches a pad ·
+            sweep the XY pad while a note rings
           </div>
         </div>
       </div>

apps/docs/src/styles.css

@@ -309,6 +309,57 @@ h2.section-title {
   text-transform: uppercase;
 }
 
+/* ---- synth panel ---- */
+.synth-rows {
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+  width: 100%;
+}
+.synth-row {
+  display: flex;
+  gap: 16px;
+  justify-content: center;
+  flex-wrap: wrap;
+  align-items: stretch;
+}
+.synth-module {
+  border: 1px solid var(--line-strong);
+  border-radius: 12px;
+  background: rgba(255, 255, 255, 0.02);
+  padding: 14px 18px 12px;
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  align-items: center;
+}
+.synth-module > .module-title {
+  font-family: var(--font-mono);
+  font-size: 10.5px;
+  letter-spacing: 0.22em;
+  text-transform: uppercase;
+  color: var(--text-faint);
+  align-self: stretch;
+  text-align: center;
+  border-bottom: 1px solid var(--line);
+  padding-bottom: 7px;
+}
+.synth-module .module-body {
+  display: flex;
+  gap: 18px;
+  align-items: center;
+  justify-content: center;
+  flex-wrap: wrap;
+  flex: 1;
+}
+.synth-pads {
+  display: flex;
+  gap: 8px;
+  justify-content: center;
+  flex-wrap: wrap;
+  align-items: center;
+}
+
 /* ---- playground ---- */
 .playground {
   display: grid;

packages/dreamknob/src/skins/SteppedKnob.tsx

@@ -30,6 +30,7 @@ export const SteppedKnob = React.forwardRef<HTMLDivElement, SteppedKnobProps>(fu
   labelColor,
   label,
   showValue = true,
+  format,
   focusRing,
   className,
   style,
@@ -92,7 +93,11 @@ export const SteppedKnob = React.forwardRef<HTMLDivElement, SteppedKnobProps>(fu
                 fontWeight={600}
                 style={{ pointerEvents: 'none' }}
               >
-                {positions ? positions[index] : ctx.value.toFixed(ctx.decimals)}
+                {positions
+                  ? positions[index]
+                  : format
+                    ? format(ctx.value)
+                    : ctx.value.toFixed(ctx.decimals)}
               </text>
             )}
             {label && (