feat: switch a preset off, or ramp it, as one thing

packages/core/src/audio/audioFxAutomation.ts

@@ -245,13 +245,24 @@ export function scheduleChainAutomation(
   chain: HfAudioFxChain,
   nodes: readonly AutomatableNode[],
   timing: AutomationTiming,
+  /** The wet/dry blend around each preset run, from `FxChainHandle.presets`. */
+  presets?: Record<string, FxParamTarget[]>,
 ): FxParamTarget[] {
   const byId = new Map(nodes.filter((n) => n.id).map((n) => [n.id as string, n.handle]));
   const scheduled: FxParamTarget[] = [];
   for (const lane of automation.lanes) {
     const parsed = parseAutomationTarget(lane.target);
-    if (!parsed || parsed.kind !== "fx") continue;
-    const targets = byId.get(parsed.nodeId)?.automation?.[parsed.param];
+    if (!parsed) continue;
+    // A whole-preset lane drives the wet/dry blend the graph wrapped its run in,
+    // rather than any node's parameter — which is the point of it: a preset's
+    // nodes share no automatable parameter, and its worklet effects expose none
+    // at all.
+    const targets =
+      parsed.kind === "preset"
+        ? presets?.[parsed.presetId]
+        : parsed.kind === "fx"
+          ? byId.get(parsed.nodeId)?.automation?.[parsed.param]
+          : undefined;
     if (!targets || targets.length === 0) continue;
     const range = resolveAutomationRange(lane.target, chain);
     if (!range) continue;

packages/core/src/audio/audioFxGraph.test.ts

@@ -624,3 +624,77 @@ describe("chain update keeps ids with their effects", () => {
     expect(handle.nodes.map((n) => n.id)).toEqual(["n2", "n1"]);
   });
 });
+
+describe("a preset's run is wrapped in a wet/dry blend", () => {
+  /** Two nodes from one preset, with an ordinary effect after them. */
+  const chainWith = (amount?: number): HfAudioFxChain => ({
+    version: 1,
+    nodes: [
+      {
+        type: "highpass",
+        id: "p1",
+        fromPreset: "telephone",
+        enabled: true,
+        ...(amount === undefined ? {} : { presetAmount: amount }),
+        params: defaultAudioFxParams("highpass"),
+      },
+      {
+        type: "lowpass",
+        id: "p2",
+        fromPreset: "telephone",
+        enabled: true,
+        params: defaultAudioFxParams("lowpass"),
+      },
+      { type: "reverb", id: "own", enabled: true, params: defaultAudioFxParams("reverb") },
+    ],
+  });
+
+  it("exposes one blend for the whole preset, not one per node", () => {
+    // The reason this exists: a preset's nodes share no automatable parameter,
+    // and its worklet effects expose no AudioParams at all, so there is nothing
+    // to aim a lane at node-by-node.
+    const built = buildFxChain(asCtx(ctx()), chainWith());
+    expect(Object.keys(built.presets)).toEqual(["telephone"]);
+    // Two gains in opposition, the same shape an effect's own mix knob has.
+    expect(built.presets.telephone).toHaveLength(2);
+  });
+
+  it("blends dry against wet at the stored amount", () => {
+    const built = buildFxChain(asCtx(ctx()), chainWith(0.25));
+    const [wet, dry] = built.presets.telephone ?? [];
+    expect(wet?.param.value).toBeCloseTo(0.25, 6);
+    expect(dry?.param.value).toBeCloseTo(0.75, 6);
+  });
+
+  it("is fully applied when nothing says otherwise", () => {
+    // Every chain written before this shipped means "all of it".
+    const [wet, dry] = buildFxChain(asCtx(ctx()), chainWith()).presets.telephone ?? [];
+    expect(wet?.param.value).toBe(1);
+    expect(dry?.param.value).toBe(0);
+  });
+
+  it("pushes a changed amount into the running graph rather than rebuilding", () => {
+    // Switching a preset off is a value change, and a rebuild would restart the
+    // audio underneath it.
+    const built = buildFxChain(asCtx(ctx()), chainWith(1));
+    expect(built.update(chainWith(0))).toBe(true);
+    const [wet, dry] = built.presets.telephone ?? [];
+    expect(wet?.param.value).toBe(0);
+    expect(dry?.param.value).toBe(1);
+  });
+
+  it("wraps nothing around effects the author placed themselves", () => {
+    const built = buildFxChain(asCtx(ctx()), chain("peaking", "reverb"));
+    expect(Object.keys(built.presets)).toEqual([]);
+  });
+
+  it("unwires the blend on dispose", () => {
+    // The wrap belongs to the chain rather than to any effect, so it is not in
+    // `handles` — without this a rebuild leaves a crossfade connected to the
+    // graph it used to bridge.
+    const c = ctx();
+    buildFxChain(asCtx(c), chainWith(0.5)).dispose();
+    const live = c.created.filter((n) => n.kind === "gain" && !n.disconnected);
+    expect(live).toEqual([]);
+  });
+});

packages/core/src/audio/audioFxGraph.ts

@@ -13,6 +13,7 @@ import {
   getAudioFxDef,
   normalizeAudioFxParams,
   type HfAudioFxChain,
+  type HfAudioFxNode,
   type HfAudioFxParamValues,
 } from "../audioFx.js";
 import { audioFxWorkletsReady, ensureAudioFxWorklets } from "./audioFxWorklets.js";
@@ -539,11 +540,45 @@ export interface FxChainHandle {
   output: AudioNode;
   /** Built effects in chain order, carrying the node ids lanes address. */
   nodes: { id?: string; type: string; handle: FxNodeHandle }[];
+  /**
+   * The wet/dry blend around each preset run, by preset id — where a
+   * whole-preset lane writes. Two gains in opposition, the same shape
+   * `mixTargets` builds for an effect's own mix knob.
+   */
+  presets: Record<string, FxParamTarget[]>;
   /** Re-parameterise in place when the shape is unchanged; false if a rebuild is needed. */
   update(chain: HfAudioFxChain): boolean;
   dispose(): void;
 }
 
+/**
+ * Consecutive nodes grouped by the preset that wrote them.
+ *
+ * `amount` comes off the nodes themselves — a preset is bypassed by setting its
+ * members' `enabled` to false everywhere else in the codebase, and the wrap has
+ * to agree with that or the switch and the lane would fight. Absent means fully
+ * applied, which is what every chain written before this shipped means.
+ */
+function presetRuns(
+  nodes: readonly HfAudioFxNode[],
+): { preset?: string; amount: number; nodes: HfAudioFxNode[] }[] {
+  const out: { preset?: string; amount: number; nodes: HfAudioFxNode[] }[] = [];
+  for (const node of nodes) {
+    const preset = node.fromPreset;
+    const last = out.at(-1);
+    if (last && last.preset === preset) last.nodes.push(node);
+    else {
+      const amount = typeof node.presetAmount === "number" ? node.presetAmount : 1;
+      out.push({
+        ...(preset ? { preset } : {}),
+        amount: Math.min(1, Math.max(0, amount)),
+        nodes: [node],
+      });
+    }
+  }
+  return out;
+}
+
 /**
  * A signature of everything that changes the graph's *shape* rather than its
  * parameter values. When this is unchanged an update can just push new values
@@ -585,21 +620,66 @@ export function buildFxChain(
   const input = ctx.createGain();
   const output = ctx.createGain();
   const handles: { id?: string; type: string; handle: FxNodeHandle }[] = [];
+  const presets: { id: string; entry: GainNode; wet: GainNode; dry: GainNode; join: GainNode }[] =
+    [];
+
+  /**
+   * A preset's consecutive nodes, wrapped in a wet/dry pair.
+   *
+   * The rest of the chain is a strict series, which is right for an effect the
+   * author placed: it is either in the path or it is not. A preset is not one
+   * effect, though — it is several the author added as a unit, and "how much of
+   * it is applied" is a question about the unit. Its nodes share no automatable
+   * parameter, and the worklet ones expose no AudioParams at all, so there is
+   * nothing to aim a lane at node-by-node. One crossfade around the run is the
+   * whole answer, and it cannot go half-wrong the way seven lanes can.
+   *
+   * Consecutive only, matching what the rack brackets: a preset pulled apart by
+   * a reorder is no longer a unit, and wrapping across the gap would route the
+   * effect between its members through the dry leg too.
+   */
+  const runs = presetRuns(enabledAudioFxNodes(chain));
 
   let tail: AudioNode = input;
-  for (const node of enabledAudioFxNodes(chain)) {
-    const handle = buildFxNode(ctx, node.type, node.params ?? {}, elapsed);
-    tail.connect(handle.input);
-    tail = handle.output;
-    handles.push({ ...(node.id ? { id: node.id } : {}), type: node.type, handle });
+  for (const run of runs) {
+    let wrap: { entry: GainNode; wet: GainNode; dry: GainNode; join: GainNode } | null = null;
+    if (run.preset) {
+      const entry = ctx.createGain();
+      const dry = ctx.createGain();
+      const wet = ctx.createGain();
+      const join = ctx.createGain();
+      wet.gain.value = run.amount;
+      dry.gain.value = 1 - run.amount;
+      tail.connect(entry);
+      // The dry leg bridges the whole run: it leaves before the first effect and
+      // rejoins after the last, which is what makes amount 0 the untouched
+      // signal rather than a quieter version of the processed one.
+      entry.connect(dry).connect(join);
+      wrap = { entry, wet, dry, join };
+      tail = entry;
+    }
+    for (const node of run.nodes) {
+      const handle = buildFxNode(ctx, node.type, node.params ?? {}, elapsed);
+      tail.connect(handle.input);
+      tail = handle.output;
+      handles.push({ ...(node.id ? { id: node.id } : {}), type: node.type, handle });
+    }
+    if (wrap && run.preset) {
+      tail.connect(wrap.wet).connect(wrap.join);
+      presets.push({ id: run.preset, ...wrap });
+      tail = wrap.join;
+    }
   }
   tail.connect(output);
 
   const shape = shapeOf(chain);
 
+  const presetTargets: Record<string, FxParamTarget[]> = {};
+  for (const p of presets) presetTargets[p.id] = mixTargets(p.wet.gain, p.dry.gain);
   return {
     input,
     output,
+    presets: presetTargets,
     nodes: handles,
     update(next) {
       if (shapeOf(next) !== shape) return false;
@@ -616,13 +696,31 @@ export function buildFxChain(
         if (node.id === undefined) delete held.id;
         else held.id = node.id;
       });
-      // `shape` is not reassigned: the early return above already established
+      // The blend is a value like any other: switching a preset off writes
+      // `presetAmount`, and pushing it into the running graph is what keeps that
+      // from being a rebuild — and from restarting the audio underneath it.
+      for (const run of presetRuns(enabledAudioFxNodes(next))) {
+        if (!run.preset) continue;
+        const wrap = presets.find((p) => p.id === run.preset);
+        if (!wrap) continue;
+        wrap.wet.gain.value = run.amount;
+        wrap.dry.gain.value = 1 - run.amount;
+      } // `shape` is not reassigned: the early return above already established
       // that `shapeOf(next)` equals it, so recomputing was a whole normalise +
       // join per observer tick to write back the string that was already there.
       return true;
     },
     dispose() {
       for (const { handle } of handles) handle.dispose();
+      // The wrap is not one of `handles` — it belongs to the chain rather than
+      // to any effect — so it has to be unwired here or a rebuild leaves a
+      // crossfade still connected to the graph it used to bridge.
+      for (const { entry, wet, dry, join } of presets) {
+        entry.disconnect();
+        wet.disconnect();
+        dry.disconnect();
+        join.disconnect();
+      }
       input.disconnect();
       output.disconnect();
     },

packages/core/src/audioAutomation.ts

@@ -79,12 +79,22 @@ export class AudioAutomationError extends Error {
 
 export const VOLUME_TARGET = "volume";
 
-export type HfAutomationTarget = { kind: "volume" } | { kind: "fx"; nodeId: string; param: string };
+export type HfAutomationTarget =
+  | { kind: "volume" }
+  | { kind: "fx"; nodeId: string; param: string }
+  | { kind: "preset"; presetId: string };
 
 /** Split a target string. Returns null for anything unrecognised. */
 export function parseAutomationTarget(target: string): HfAutomationTarget | null {
   if (target === VOLUME_TARGET) return { kind: "volume" };
   const parts = target.split(".");
+  // `fx.preset.<id>` before the 3-part fx form, because it IS a 3-part fx form
+  // with a reserved node id — an effect can never be called "preset", since ids
+  // are minted `n1`, `n2`, ….
+  if (parts.length === 3 && parts[0] === "fx" && parts[1] === PRESET_TARGET_KEY) {
+    const presetId = parts[2];
+    return presetId ? { kind: "preset", presetId } : null;
+  }
   if (parts.length !== 3 || parts[0] !== "fx") return null;
   const [, nodeId, param] = parts;
   if (!nodeId || !param) return null;
@@ -95,6 +105,33 @@ export function fxAutomationTarget(nodeId: string, param: string): string {
   return `fx.${nodeId}.${param}`;
 }
 
+/** The reserved node-id slot that marks a whole-preset target. */
+const PRESET_TARGET_KEY = "preset";
+
+/**
+ * How much of a preset is applied, 0..1.
+ *
+ * A preset's nodes share no automatable parameter — and its worklet effects
+ * expose no AudioParams at all — so there is nothing to aim a lane at
+ * node-by-node. The graph wraps a preset's run in a wet/dry pair instead, and
+ * this drives the blend: 0 is the dry signal untouched, 1 is the preset fully
+ * applied, and between them it crossfades.
+ */
+export function presetAutomationTarget(presetId: string): string {
+  return `fx.${PRESET_TARGET_KEY}.${presetId}`;
+}
+
+/** 0..1 blend, the same shape as a wet/dry mix knob. */
+export const PRESET_RANGE: AutomationRange = {
+  min: 0,
+  max: 1,
+  step: 0.01,
+  unit: "",
+  label: "Amount",
+  scale: "linear",
+  default: 1,
+};
+
 /**
  * The value range a lane is drawn and clamped against.
  *
@@ -136,6 +173,13 @@ export function resolveAutomationRange(
   const parsed = parseAutomationTarget(target);
   if (!parsed) return null;
   if (parsed.kind === "volume") return VOLUME_RANGE;
+  if (parsed.kind === "preset") {
+    // Only for a preset the chain actually carries, so a lane left behind by a
+    // removed preset resolves to nothing and is dropped at read time — the same
+    // contract an orphaned node lane has.
+    const present = chain?.nodes.some((n) => n.fromPreset === parsed.presetId);
+    return present ? { ...PRESET_RANGE, label: `${parsed.presetId} · Amount` } : null;
+  }
   const node = chain?.nodes.find((n) => n.id === parsed.nodeId);
   if (!node) return null;
   const def = getAudioFxDef(node.type);

packages/core/src/audioFx.ts

@@ -832,10 +832,21 @@ export interface HfAudioFxNode {
    * effect type and its bands stay ordinary filters underneath.
    */
   fromEq?: string;
+
   /**
+   * How much of this node's preset is applied, 0..1 — the wet/dry blend the
+   * graph wraps its run in.
+   *
+   * On every node of the run rather than beside the chain, because the chain has
+   * nowhere else to put it: `HfAudioFxChain` is a version and a list of nodes,
+   * and a preset is defined by which nodes carry its tag. The graph reads it off
+   * the first node of each run. Absent means fully applied, which is what every
+   * chain written before this means.
+   */
+  presetAmount?: number /**
    * Set on the gain stage the leveller writes, so re-running replaces it rather
    * than stacking a second one — the same contract `fromCarve` has.
-   */
+   */;
   fromLeveller?: boolean;
   /** Absent means enabled — chain files written before the field existed still load. */
   enabled?: boolean;
@@ -890,6 +901,7 @@ export function parseAudioFxChain(json: string): HfAudioFxChain {
       label?: unknown;
       fromEq?: unknown;
       fromLeveller?: unknown;
+      presetAmount?: unknown;
     };
     if (typeof node.type !== "string" || !BY_ID.has(node.type)) {
       throw new AudioFxChainError(`Node ${i} has unknown effect type: ${String(node.type)}`);
@@ -907,6 +919,11 @@ export function parseAudioFxChain(json: string): HfAudioFxChain {
       ...(typeof node.label === "string" && node.label ? { label: node.label } : {}),
       ...(typeof node.fromEq === "string" && node.fromEq ? { fromEq: node.fromEq } : {}),
       ...(node.fromLeveller === true ? { fromLeveller: true as const } : {}),
+      // Clamped on the way in: the blend is two gains in opposition, and a value
+      // outside 0..1 makes the dry leg negative rather than simply loud.
+      ...(typeof node.presetAmount === "number" && Number.isFinite(node.presetAmount)
+        ? { presetAmount: Math.min(1, Math.max(0, node.presetAmount)) }
+        : {}),
       enabled: node.enabled !== false,
       params: normalizeAudioFxParams(
         node.type,
@@ -934,6 +951,11 @@ export function serializeAudioFxChain(chain: HfAudioFxChain): string {
       ...(node.label ? { label: node.label } : {}),
       ...(node.fromEq ? { fromEq: node.fromEq } : {}),
       ...(node.fromLeveller === true ? { fromLeveller: true } : {}),
+      // Omitted when fully applied, so an untouched preset does not grow a field
+      // in every chain that carries one.
+      ...(typeof node.presetAmount === "number" && node.presetAmount !== 1
+        ? { presetAmount: node.presetAmount }
+        : {}),
       ...(node.enabled === false ? { enabled: false } : {}),
       params: normalizeAudioFxParams(node.type, node.params),
     })),