diff --git a/src/core/commands/portCommands.ts b/src/core/commands/portCommands.ts
index fa564539..88ccd411 100644
--- a/src/core/commands/portCommands.ts
+++ b/src/core/commands/portCommands.ts
@@ -1,6 +1,7 @@
 import {
   BEHAVIOR_PARAM,
   declaresPropertyPorts,
+  declaresSoundFxPorts,
   declaresVariablePorts,
   type DeclaredPort,
   findNode,
@@ -17,6 +18,8 @@ import {
   OBJECT_BEHAVIOR_PARAM,
   propertyTargetOf,
   SHADER_CALL,
+  SOUND_FX_INPUT,
+  soundFxSourceOf,
   variablesSourceOf,
 } from '../graph';
 import { isGraphAsset } from '../model/Asset';
@@ -342,6 +345,54 @@ export class RenamePortCommand extends RenameCommand {
     if (ports.some((p) => p.key === to)) throw new CommandError(`"${to}" already exists`);
     node.ports = ports.map((p) => (p.key === from ? { ...p, key: to } : p));
     for (const site of sites) carryPort(site, from, to);
+    if (node.type === SOUND_FX_INPUT) renameSoundFxParamPorts(project, this.assetId, from, to);
+  }
+}
+
+/** The default of a sound FX parameter (#311): what it is wherever no `Play sound` hands a value in. */
+export class SetPortDefaultCommand implements Command {
+  readonly label: string;
+  private was: number | undefined;
+
+  constructor(
+    private readonly assetId: string,
+    private readonly nodeId: string,
+    private readonly key: string,
+    private readonly value: number,
+  ) {
+    this.label = `Set default of ${key}`;
+  }
+
+  execute(project: Project): void {
+    const node = requireNode(project, this.assetId, this.nodeId);
+    if (node.type !== SOUND_FX_INPUT) throw new CommandError('Only a sound FX Input has defaults');
+    const port = (node.ports ?? []).find((p) => p.key === this.key);
+    if (!port) throw new CommandError(`Port "${this.key}" not found`);
+    if (!Number.isFinite(this.value)) throw new CommandError('A default is a number');
+    this.was = port.default;
+    this.mark(node, this.value);
+  }
+
+  undo(project: Project): void {
+    this.mark(requireNode(project, this.assetId, this.nodeId), this.was);
+  }
+
+  private mark(node: GraphNode, value: number | undefined): void {
+    node.ports = (node.ports ?? []).map((port) => {
+      if (port.key !== this.key) return port;
+      const { default: _, ...plain } = port;
+      return value === undefined ? plain : { ...plain, default: value };
+    });
+  }
+}
+
+/** A renamed parameter of a sound FX, followed into every node that sets it. */
+function renameSoundFxParamPorts(project: Project, fxId: string, from: string, to: string): void {
+  for (const asset of project.assets) {
+    if (!isGraphAsset(asset)) continue;
+    for (const node of asset.graph.nodes)
+      if (declaresSoundFxPorts(node.type) && soundFxSourceOf(node.params) === fxId)
+        renamePortOn(asset.graph, node, from, to);
   }
 }
 
diff --git a/src/core/graph/Graph.ts b/src/core/graph/Graph.ts
index b47d5259..569980b6 100644
--- a/src/core/graph/Graph.ts
+++ b/src/core/graph/Graph.ts
@@ -6,7 +6,8 @@ export type { DeclaredPortKind } from '../properties/kinds';
 /**
  * `exec` carries control flow, the others values; `any` accepts every value type. `vec3` is a
  * colour inside a shader graph, where the values are GLSL and no behavior node ever sees one;
- * `picture` is what a shader's Pass draws (#301), for the nodes that read a picture.
+ * `picture` is what a shader's Pass draws (#301), for the nodes that read a picture. `fxparams` is
+ * the values a `Play sound` hands to the parameters of its sound FX (#311).
  */
 export type PortType =
   | 'exec'
@@ -19,6 +20,7 @@ export type PortType =
   | 'vec3'
   | 'picture'
   | 'audio'
+  | 'fxparams'
   | 'any';
 
 export interface PortRef {
@@ -70,6 +72,8 @@ export interface DeclaredPort {
    * from it. On a start node, a node running the behavior has it picked in advance as well.
    */
   machine?: string;
+  /** On a parameter of a sound FX Input: its value wherever nobody hands one in (#311). */
+  default?: number;
 }
 
 export function declaredPortType(kind: DeclaredPortKind): PortType {
@@ -183,12 +187,14 @@ export function graphFingerprint(graph: Graph): string {
 /**
  * A number may feed a colour: the shader compiler spreads it over the three channels. A picture is
  * no value a calculation could take, so like `exec` it goes only where a picture is read – and a
- * sound on its way through effects (#311) only where a sound goes in.
+ * sound on its way through effects (#311) only where a sound goes in, and its parameters only to a
+ * `Play sound`.
  */
 export function portsCompatible(from: PortType, to: PortType): boolean {
   if (from === 'exec' || to === 'exec') return from === to;
   if (from === 'picture' || to === 'picture') return from === to;
   if (from === 'audio' || to === 'audio') return from === to;
+  if (from === 'fxparams' || to === 'fxparams') return from === to;
   if (from === 'number' && to === 'vec3') return true;
   return from === to || from === 'any' || to === 'any';
 }
diff --git a/src/core/graph/NodeContext.ts b/src/core/graph/NodeContext.ts
index dd0e60f1..3e436ea1 100644
--- a/src/core/graph/NodeContext.ts
+++ b/src/core/graph/NodeContext.ts
@@ -1,6 +1,7 @@
 import type { AnimationPlayer } from '../model/animation';
 import type { Mat } from '../model/matrix';
 import type { Position, PropertyBag } from '../model/Properties';
+import type { FxParams } from '../soundfx/nodes';
 import { type ChainTransform, composeAlongChain } from '../model/walk';
 import { enabledAlongChain } from '../properties/enabled';
 import { localMatrixOf, positionOf, transformOf } from '../properties/transform';
@@ -238,8 +239,16 @@ export interface NodeContext {
    * a sound is something a thing in the world is doing. `detached` gives that up on purpose, for
    * the one case where the rule is in the way: the death sound of an object that destroys itself.
    * `fx` names a sound FX asset the voice is played through (#311); `''` plays it as it is.
+   * `fxParams` are values for its parameters; one not given is the default the FX declares.
    */
-  playSound(assetId: string, volume: number, loop: boolean | undefined, detached: boolean, fx: string): void;
+  playSound(
+    assetId: string,
+    volume: number,
+    loop: boolean | undefined,
+    detached: boolean,
+    fx: string,
+    fxParams: FxParams,
+  ): void;
   /** Silences every voice of that sound; `''` silences everything this run started. */
   stopSound(assetId: string): void;
   /**
diff --git a/src/core/graph/NodeRegistry.ts b/src/core/graph/NodeRegistry.ts
index 7b96310b..1455e7aa 100644
--- a/src/core/graph/NodeRegistry.ts
+++ b/src/core/graph/NodeRegistry.ts
@@ -213,7 +213,8 @@ function isInlinePort(port: PortDef): boolean {
     port.type !== 'object' &&
     port.type !== 'struct' &&
     port.type !== 'picture' &&
-    port.type !== 'audio'
+    port.type !== 'audio' &&
+    port.type !== 'fxparams'
   );
 }
 
diff --git a/src/core/graph/lookup.ts b/src/core/graph/lookup.ts
index 65347e16..8a6d1639 100644
--- a/src/core/graph/lookup.ts
+++ b/src/core/graph/lookup.ts
@@ -1,7 +1,7 @@
 import type { AnimationClip } from '../model/animation';
 import type { VectorPoint } from '../model/Asset';
 import type { PropertyBag } from '../model/Properties';
-import type { Graph } from './Graph';
+import type { DeclaredPort, Graph } from './Graph';
 
 /** What running another behavior's graph in place needs: its nodes, its variable defaults, its name. */
 export interface BehaviorProgram {
@@ -17,6 +17,12 @@ export interface ShaderFunction {
   graph: Graph;
 }
 
+/** A sound FX as a node naming it sees it: the parameters its Input declares (#311). */
+export interface SoundFxShape {
+  name: string;
+  params: readonly DeclaredPort[];
+}
+
 /** One state of a machine: the node id is what a port and the runtime hold, the name is the label. */
 export interface MachineState {
   id: string;
@@ -52,6 +58,7 @@ export interface GraphLookup {
   behavior(assetId: string): BehaviorProgram | null;
   /** A shader function's graph, which a call node takes its ports from and the compiler sets in (#303). */
   shaderFunction(assetId: string): ShaderFunction | null;
+  soundFx(assetId: string): SoundFxShape | null;
   machine(assetId: string): StateMachine | null;
   curve(assetId: string): readonly VectorPoint[] | null;
   /** A Struct asset as a run knows it: a name and field names, nothing else travels (#254). */
@@ -90,6 +97,7 @@ export interface ValueTyping {
 export const NO_LOOKUP: GraphLookup = {
   behavior: () => null,
   shaderFunction: () => null,
+  soundFx: () => null,
   machine: () => null,
   curve: () => null,
   structType: () => null,
diff --git a/src/core/graph/nested.ts b/src/core/graph/nested.ts
index 55821f40..77407b7c 100644
--- a/src/core/graph/nested.ts
+++ b/src/core/graph/nested.ts
@@ -28,10 +28,29 @@ const ON_START = 'OnStart';
 export const SHADER_FUNCTION_INPUT = 'ShaderFunctionInput';
 export const SHADER_FUNCTION_OUTPUT = 'ShaderFunctionOutput';
 export const SHADER_CALL = 'ShaderCall';
+/** The two ends of a sound FX graph and the behavior node naming its parameters (#311). */
+export const SOUND_FX_INPUT = 'SoundFxInput';
+export const SOUND_FX_OUTPUT = 'SoundFxOutput';
+export const SOUND_FX_PARAMETERS = 'SoundFxParameters';
+const PLAY_SOUND = 'PlaySound';
 
 export const BEHAVIOR_PARAM = 'behavior';
 export const FUNCTION_PARAM = 'function';
 export const VARIABLES_PARAM = 'variablesAsset';
+export const SOUND_FX_PARAM = 'soundFxAsset';
+
+/** Whose parameters a `Sound FX parameters` node sets. */
+export const SOUND_FX_SETTING: PropertyDef = {
+  key: SOUND_FX_PARAM,
+  label: 'Sound FX',
+  kind: 'asset',
+  default: '',
+  assetTypes: ['soundfx'],
+};
+
+export function soundFxSourceOf(params: PropertyBag): string {
+  return textOf(params[SOUND_FX_PARAM] ?? '');
+}
 
 /** Whose declarations a `Variables` node reads; empty is the behavior the node sits in. */
 export const VARIABLES_SETTING: PropertyDef = {
@@ -71,6 +90,11 @@ export function declaresPropertyPorts(type: string): boolean {
   return type === PROPERTIES;
 }
 
+/** Nodes whose declared ports are parameters of the sound FX they name. */
+export function declaresSoundFxPorts(type: string): boolean {
+  return type === SOUND_FX_PARAMETERS;
+}
+
 /** Identifier-like, and not `exec`: that key belongs to the fixed flow port of every terminal node. */
 export function isValidPortName(name: string): boolean {
   return isValidFieldName(name) && name !== 'exec';
@@ -127,13 +151,15 @@ export function isTerminalType(type: string): boolean {
     type === BEHAVIOR_START ||
     type === BEHAVIOR_END ||
     type === SHADER_FUNCTION_INPUT ||
-    type === SHADER_FUNCTION_OUTPUT
+    type === SHADER_FUNCTION_OUTPUT ||
+    type === SOUND_FX_INPUT ||
+    type === SOUND_FX_OUTPUT
   );
 }
 
 /** The terminal whose ports a caller passes in, rather than takes out. */
 export function isEntryTerminal(type: string): boolean {
-  return type === BEHAVIOR_START || type === SHADER_FUNCTION_INPUT;
+  return type === BEHAVIOR_START || type === SHADER_FUNCTION_INPUT || type === SOUND_FX_INPUT;
 }
 
 export function isTerminalNode(node: GraphNode): boolean {
@@ -354,6 +380,7 @@ export function ghostProblem(node: GraphNode, graph: Graph, def: NodeDef): strin
 export function callProblem(node: GraphNode, lookup: GraphLookup, ownerId = ''): string | null {
   if (node.type === ON_BEHAVIOR) return listenProblem(node, lookup, ownerId);
   if (node.type === SHADER_CALL) return functionCallProblem(node, lookup, ownerId);
+  if (node.type === SOUND_FX_PARAMETERS) return soundFxParametersProblem(node, lookup);
   if (node.type !== RUN_BEHAVIOR) return lerpProblem(node, lookup);
   const id = textOf(node.params[BEHAVIOR_PARAM] ?? '');
   if (!id) return 'No behavior picked';
@@ -398,6 +425,27 @@ function functionCallProblem(node: GraphNode, lookup: GraphLookup, ownerId: stri
   return null;
 }
 
+function soundFxParametersProblem(node: GraphNode, lookup: GraphLookup): string | null {
+  const id = soundFxSourceOf(node.params);
+  if (!id) return 'No sound FX picked';
+  return lookup.soundFx(id) ? null : 'That sound FX is gone';
+}
+
+/**
+ * A `Play sound` whose parameters come from a node naming another sound FX than the one it plays:
+ * the names that FX does not know are left out, so the values would go nowhere. Only said where both
+ * are picked in place – one coming over an edge may be either.
+ */
+export function soundFxParamsMismatch(node: GraphNode, graph: Graph): string | null {
+  if (node.type !== PLAY_SOUND || edgesInto(graph, node.id, 'fx').length > 0) return null;
+  const played = textOf(node.params.fx ?? '');
+  const edge = edgesInto(graph, node.id, 'fxParams')[0];
+  const from = edge && findNode(graph, edge.from.node);
+  if (!played || from?.type !== SOUND_FX_PARAMETERS) return null;
+  const named = soundFxSourceOf(from.params);
+  return named && named !== played ? 'The parameters are for another sound FX' : null;
+}
+
 /** The ids the nodes of one type in that graph name in `param`, picked or not found alike. */
 function namedBy(graph: Graph, type: string, param: string): string[] {
   return graph.nodes
diff --git a/src/core/graph/nodes/action/PlaySound.ts b/src/core/graph/nodes/action/PlaySound.ts
index 44e8b1e8..407df093 100644
--- a/src/core/graph/nodes/action/PlaySound.ts
+++ b/src/core/graph/nodes/action/PlaySound.ts
@@ -1,3 +1,5 @@
+import { isStruct } from '../../../model/Properties';
+import type { FxParams } from '../../../soundfx/nodes';
 import type { NodeDef, PortDef } from '../../NodeRegistry';
 import { asBoolean, asNumber, asString, type Value } from '../../values';
 import { exec, num, soundFxPort, soundPort, withDefault } from '../shared';
@@ -56,8 +58,17 @@ export const PlaySound: NodeDef = {
     "leaves the asset's own setting alone or overrules it, so the asset says what the sound is and " +
     'the node only colors it. Each play is a voice of its own: firing this twice in a row is heard ' +
     'twice, overlapping. The sound belongs to this object and stops when the object is destroyed, ' +
-    'unless "detached" is on. "fx" sends it through a sound FX asset; left empty, it plays as it is.',
-  inputs: [exec(), soundPort(), withDefault(num('volume'), 1), loopPort(), detachedPort(), soundFxPort()],
+    'unless "detached" is on. "fx" sends it through a sound FX asset; left empty, it plays as it is. ' +
+    '"fx params" takes values for its parameters from a Sound FX parameters node.',
+  inputs: [
+    exec(),
+    soundPort(),
+    withDefault(num('volume'), 1),
+    loopPort(),
+    detachedPort(),
+    soundFxPort(),
+    { key: 'fxParams', label: 'fx params', type: 'fxparams' },
+  ],
   outputs: [exec()],
   params: [],
   run: (ctx, inputs) => {
@@ -69,7 +80,16 @@ export const PlaySound: NodeDef = {
         loopChoice(inputs.loop),
         asBoolean(inputs.detached),
         asString(inputs.fx),
+        fxParamsOf(inputs.fxParams),
       );
     return { next: 'exec' };
   },
 };
+
+/** The numbers of a parameter bundle; anything else hands in none. */
+function fxParamsOf(value: Value | undefined): FxParams {
+  if (!isStruct(value)) return {};
+  const params: Record<string, number> = {};
+  for (const [key, item] of Object.entries(value)) if (typeof item === 'number') params[key] = item;
+  return params;
+}
diff --git a/src/core/graph/nodes/data/SoundFxParameters.ts b/src/core/graph/nodes/data/SoundFxParameters.ts
new file mode 100644
index 00000000..e7c598d9
--- /dev/null
+++ b/src/core/graph/nodes/data/SoundFxParameters.ts
@@ -0,0 +1,37 @@
+import type { StructValue } from '../../../model/Properties';
+import { SOUND_FX_PARAMETERS, SOUND_FX_SETTING, soundFxSourceOf } from '../../nested';
+import type { NodeDef } from '../../NodeRegistry';
+import { asNumber } from '../../values';
+
+/**
+ * Values for the parameters of one sound FX (#311), picked from those its Input declares the way a
+ * Variables node picks variables. Each picked one is a number input starting at the FX's default;
+ * the bundle goes into the `fx params` input of a `Play sound`.
+ */
+export const SoundFxParameters: NodeDef = {
+  type: SOUND_FX_PARAMETERS,
+  label: 'Sound FX parameters',
+  category: 'data',
+  description:
+    'Values for the parameters of a sound FX, for the "fx params" input of a Play sound. Pick the parameters to set; one not picked keeps the default its Input gives it.',
+  inputs: [],
+  outputs: [{ key: 'params', label: 'params', type: 'fxparams' }],
+  params: [SOUND_FX_SETTING],
+  declaresPorts: 'inputs',
+  portKinds: ['number'],
+  declaredPort: (port, node, _graph, lookup) => {
+    const declared = lookup.soundFx(soundFxSourceOf(node.params))?.params.find((p) => p.key === port.key);
+    const value = declared?.default ?? 0;
+    return {
+      key: port.key,
+      label: port.key,
+      type: 'number',
+      default: value,
+      field: { key: port.key, label: port.key, kind: 'number', default: value },
+    };
+  },
+  run: (_ctx, inputs, _params, def) => {
+    const values: StructValue = Object.fromEntries(def.inputs.map((p) => [p.key, asNumber(inputs[p.key])]));
+    return { outputs: { params: values } };
+  },
+};
diff --git a/src/core/graph/nodes/index.ts b/src/core/graph/nodes/index.ts
index 03f5f97f..13758769 100644
--- a/src/core/graph/nodes/index.ts
+++ b/src/core/graph/nodes/index.ts
@@ -89,6 +89,7 @@ import { Or } from './data/Or';
 import { Owner } from './data/Owner';
 import { PackStruct } from './data/PackStruct';
 import { Properties } from './data/Properties';
+import { SoundFxParameters } from './data/SoundFxParameters';
 import { Parent } from './data/Parent';
 import { Random } from './data/Random';
 import { RenderLayerOf } from './data/RenderLayerOf';
@@ -297,6 +298,7 @@ export const BUILT_IN_NODES: readonly NodeDef[] = [
   StopAnimation,
   PlaySound,
   StopSound,
+  SoundFxParameters,
   LoadScene,
   Log,
   StopGame,
diff --git a/src/core/model/graphLookup.ts b/src/core/model/graphLookup.ts
index 0af9ac05..f89949fb 100644
--- a/src/core/model/graphLookup.ts
+++ b/src/core/model/graphLookup.ts
@@ -1,4 +1,5 @@
 import type { GraphLookup } from '../graph/lookup';
+import { SOUND_FX_INPUT, terminalNode } from '../graph/nested';
 import { startStateOf, statesOf, transitionsOf } from '../graph/stateMachine';
 import { pictureSize } from '../properties/aspect';
 import { resolveAssetProps } from '../properties/resolve';
@@ -34,6 +35,12 @@ export function graphLookup(project: Project): GraphLookup {
       };
     },
     shaderFunction: shaderFunctionsOf(project),
+    soundFx: (assetId) => {
+      const asset = findAssetOf(project, assetId, 'soundfx');
+      return asset
+        ? { name: asset.name, params: terminalNode(asset.graph, SOUND_FX_INPUT)?.ports ?? [] }
+        : null;
+    },
     machine: (assetId) => {
       const asset = findAssetOf(project, assetId, 'statemachine');
       if (!asset) return null;
diff --git a/src/core/soundfx/compile.ts b/src/core/soundfx/compile.ts
index 0363d47d..c3f6de91 100644
--- a/src/core/soundfx/compile.ts
+++ b/src/core/soundfx/compile.ts
@@ -1,10 +1,13 @@
 import { graphEmitter } from '../graph/emitGraph';
-import { type Graph, graphFingerprint } from '../graph/Graph';
+import { type DeclaredPort, type Graph, graphFingerprint, type GraphNode } from '../graph/Graph';
+import { terminalNode } from '../graph/nested';
+import { inlineValue, nodeDef } from '../graph/NodeRegistry';
+import { asNumber } from '../graph/values';
 import type { SoundFxAsset } from '../model/Asset';
-import { nodeDef } from '../graph/NodeRegistry';
 import {
-  DRY,
-  type FxChain,
+  EMPTY_PLAN,
+  type FxAmount,
+  type FxPlan,
   isSoundFxNodeDef,
   SOUND_FX_INPUT,
   SOUND_FX_OUTPUT,
@@ -13,7 +16,7 @@ import {
 
 export interface SoundFxBuild {
   /** Null while the graph has a problem – a sound played through it is then played dry. */
-  compiled: FxChain | null;
+  compiled: FxPlan | null;
   /** How many nodes between Input and Output the sound passes. */
   effects: number;
   /** Per node id, what keeps the graph from compiling. */
@@ -22,33 +25,64 @@ export interface SoundFxBuild {
   reason: string;
 }
 
+/** What travels along an edge of a sound FX graph: the sound so far, or a number. */
+type FxValue = { plan: FxPlan } | { amount: FxAmount };
+
+/** The parameters the Input declares, in their order, each with its default. */
+export function soundFxParams(graph: Graph): readonly DeclaredPort[] {
+  return terminalNode(graph, SOUND_FX_INPUT)?.ports ?? [];
+}
+
+function inputOutputs(node: GraphNode): Record<string, FxValue> {
+  const outputs: Record<string, FxValue> = { out: { plan: EMPTY_PLAN } };
+  for (const port of node.ports ?? [])
+    outputs[port.key] = { amount: { value: port.default ?? 0, param: port.key } };
+  return outputs;
+}
+
 /**
  * A sound FX graph to the line a voice is sent along: walked back from the Output to the Input, every
  * node on the way adding what it does. An input takes one edge, so the line never forks on its way
- * to the Output; a node fed from nowhere is a problem rather than silence.
+ * to the Output; a node fed from nowhere is a problem rather than silence. A number fed from a
+ * parameter stays open in the plan until a voice is started (#311).
  */
 export function compileSoundFx(graph: Graph): SoundFxBuild {
-  const walk = graphEmitter<SoundFxNodeDef, FxChain>(graph, {
+  const walk = graphEmitter<SoundFxNodeDef, FxValue>(graph, {
     isDef: isSoundFxNodeDef,
     noun: 'sound FX',
-    // Only reached with every input fed, so whatever is not the Input has its sound arriving.
-    emit: (def, inputs, node) => ({ out: def.emit(inputs.in ?? DRY, node.params) }),
-    unfed: (node) => {
+    emit: (def, inputs, node) => {
+      if (node.type === SOUND_FX_INPUT) return inputOutputs(node);
+      const amounts: Record<string, FxAmount> = {};
+      for (const [key, value] of Object.entries(inputs)) if ('amount' in value) amounts[key] = value.amount;
+      const arriving = inputs.in;
+      const plan = arriving && 'plan' in arriving ? arriving.plan : EMPTY_PLAN;
+      return { out: { plan: def.emit(plan, amounts) } };
+    },
+    unfed: (node, port) => {
+      if (port.type === 'number') return { amount: { value: asNumber(inlineValue(node, port)) } };
       walk.problem(node, 'Nothing comes in: connect it to the Input');
       return null;
     },
+    conform: (node, port, value) => {
+      if ((port.type === 'audio') === 'plan' in value) return value;
+      walk.problem(
+        node,
+        port.type === 'audio' ? `"${port.label}" takes a sound` : `"${port.label}" takes a number`,
+      );
+      return null;
+    },
   });
 
   const output = graph.nodes.find((n) => n.type === SOUND_FX_OUTPUT);
   if (!output) return { compiled: null, effects: 0, problems: walk.problems, reason: 'No Output node' };
-  const chain = walk.input(output, nodeDef(SOUND_FX_OUTPUT)!.inputs[0]!);
+  const arrived = walk.input(output, nodeDef(SOUND_FX_OUTPUT)!.inputs[0]!);
   const failed = walk.firstProblem();
-  if (failed !== null || !chain)
+  if (failed !== null || !arrived || !('plan' in arrived))
     return { compiled: null, effects: 0, problems: walk.problems, reason: failed ?? 'Cannot compile' };
   const effects = graph.nodes.filter(
     (n) => walk.reached(n) && n.type !== SOUND_FX_INPUT && n.type !== SOUND_FX_OUTPUT,
   ).length;
-  return { compiled: chain, effects, problems: walk.problems, reason: '' };
+  return { compiled: arrived.plan, effects, problems: walk.problems, reason: '' };
 }
 
 const builds = new Map<string, { fingerprint: string; build: SoundFxBuild }>();
diff --git a/src/core/soundfx/nodes.ts b/src/core/soundfx/nodes.ts
index d12287ec..b4eb0cfc 100644
--- a/src/core/soundfx/nodes.ts
+++ b/src/core/soundfx/nodes.ts
@@ -1,7 +1,10 @@
+import type { DeclaredPort } from '../graph/Graph';
+import { SOUND_FX_INPUT, SOUND_FX_OUTPUT } from '../graph/nested';
 import type { NodeDef, PortDef } from '../graph/NodeRegistry';
-import type { PropertyBag } from '../model/Properties';
 import type { FlatDef } from '../properties/PropertySchema';
 
+export { SOUND_FX_INPUT, SOUND_FX_OUTPUT };
+
 /** The filter shapes the EQ uses – Web Audio's names, so the player hands them on as they are. */
 export type FxFilter = 'lowshelf' | 'peaking' | 'highshelf';
 
@@ -21,45 +24,92 @@ export interface FxChain {
 
 export const DRY: FxChain = { pitch: 0, stages: [] };
 
+/**
+ * A number of the graph as the compiler knows it: typed in, or a parameter of the Input that a
+ * `Play sound` may hand a value for (#311). `value` is what it is otherwise, and a parameter is held
+ * to the row it ends in only once its value is known.
+ */
+export interface FxAmount {
+  value: number;
+  param?: string;
+  min?: number;
+  max?: number;
+}
+
+export type FxStagePlan =
+  | { kind: 'gain'; db: FxAmount }
+  | { kind: 'filter'; filter: FxFilter; frequency: number; gain: FxAmount; q: number };
+
+/** A chain with its parameters still open: compiled once, filled in for every voice by `fxChainOf`. */
+export interface FxPlan {
+  pitch: readonly FxAmount[];
+  stages: readonly FxStagePlan[];
+}
+
+export const EMPTY_PLAN: FxPlan = { pitch: [], stages: [] };
+
+/** Values for the parameters, by name; a name the plan does not have is left out. */
+export type FxParams = Readonly<Record<string, number>>;
+
 /**
  * A node of a sound FX graph (#311). It never runs: `emit` says what it does to the sound arriving
- * at its one input. Input and Output have a side less and no effect of their own.
+ * at its one audio input, given the numbers at its other inputs. Input and Output have no effect.
  */
 export interface SoundFxNodeDef extends NodeDef {
   category: 'sound';
-  emit(chain: FxChain, params: PropertyBag): FxChain;
+  emit(plan: FxPlan, amounts: Readonly<Record<string, FxAmount>>): FxPlan;
 }
 
 export function isSoundFxNodeDef(def: NodeDef): def is SoundFxNodeDef {
   return def.category === 'sound' && 'emit' in def;
 }
 
-export const SOUND_FX_INPUT = 'SoundFxInput';
-export const SOUND_FX_OUTPUT = 'SoundFxOutput';
-
 const audioIn: PortDef = { key: 'in', label: 'in', type: 'audio' };
 const audioOut: PortDef = { key: 'out', label: 'out', type: 'audio' };
 
-function numberParam(key: string, label: string, min: number, max: number, step: number): FlatDef<'number'> {
+function numberRow(key: string, label: string, min: number, max: number, step: number): FlatDef<'number'> {
   return { key, label, kind: 'number', default: 0, min, max, step };
 }
 
-/** A param's value held to its row, so a hand-edited project cannot blow a speaker. */
-function read(params: PropertyBag, def: FlatDef<'number'>): number {
-  const value = Number(params[def.key] ?? def.default);
-  if (!Number.isFinite(value)) return def.default;
-  return Math.max(def.min ?? -Infinity, Math.min(def.max ?? Infinity, value));
+/** An input taking a number: typed in under the key the setting had, or fed from a parameter. */
+function numberIn(row: FlatDef<'number'>): PortDef {
+  return { key: row.key, label: row.label, type: 'number', field: row };
+}
+
+function holdTo(value: number, row: FlatDef<'number'>): number {
+  if (!Number.isFinite(value)) return row.default;
+  return Math.max(row.min ?? -Infinity, Math.min(row.max ?? Infinity, value));
+}
+
+/** The amount at an input, held to its row, so a hand-edited project cannot blow a speaker. */
+function held(amount: FxAmount | undefined, row: FlatDef<'number'>): FxAmount {
+  if (!amount) return { value: row.default };
+  const value = holdTo(amount.value, row);
+  if (amount.param === undefined) return { value };
+  return { value, param: amount.param, min: row.min, max: row.max };
+}
+
+/** Whether an amount does nothing however the sound is played: a typed-in 0. */
+const isNone = (amount: FxAmount) => amount.param === undefined && amount.value === 0;
+
+/** A parameter of the Input as the nodes it feeds see it. */
+export function soundFxParamPort(port: DeclaredPort): PortDef {
+  return { key: port.key, label: port.key, type: 'number' };
 }
 
 export const SoundFxInput: SoundFxNodeDef = {
   type: SOUND_FX_INPUT,
   label: 'Input',
   category: 'sound',
-  description: 'The sound as the Play sound node starts it, before any effect.',
+  description:
+    'The sound as the Play sound node starts it, before any effect. Every parameter declared here is a number output with a default; a Play sound can hand in other values through a Sound FX parameters node.',
   inputs: [],
   outputs: [audioOut],
   params: [],
-  emit: (chain) => chain,
+  declaresPorts: 'outputs',
+  portKinds: ['number'],
+  declaredPort: (port) => soundFxParamPort(port),
+  emit: (plan) => plan,
 };
 
 export const SoundFxOutput: SoundFxNodeDef = {
@@ -70,10 +120,10 @@ export const SoundFxOutput: SoundFxNodeDef = {
   inputs: [audioIn],
   outputs: [],
   params: [],
-  emit: (chain) => chain,
+  emit: (plan) => plan,
 };
 
-const GAIN = numberParam('gain', 'Gain (dB)', -60, 24, 0.5);
+const GAIN = numberRow('gain', 'Gain (dB)', -60, 24, 0.5);
 
 export const SoundFxGain: SoundFxNodeDef = {
   type: 'SoundFxGain',
@@ -81,17 +131,16 @@ export const SoundFxGain: SoundFxNodeDef = {
   category: 'sound',
   description:
     'Makes the sound louder or quieter, in decibels: 0 leaves it as it is, -6 is about half as loud, +6 twice. Above 0 it can clip.',
-  inputs: [audioIn],
+  inputs: [audioIn, numberIn(GAIN)],
   outputs: [audioOut],
-  params: [GAIN],
-  emit: (chain, params) => {
-    const db = read(params, GAIN);
-    if (db === 0) return chain;
-    return { ...chain, stages: [...chain.stages, { kind: 'gain', gain: 10 ** (db / 20) }] };
+  params: [],
+  emit: (plan, amounts) => {
+    const db = held(amounts.gain, GAIN);
+    return isNone(db) ? plan : { ...plan, stages: [...plan.stages, { kind: 'gain', db }] };
   },
 };
 
-const SEMITONES = numberParam('semitones', 'Semitones', -24, 24, 1);
+const SEMITONES = numberRow('semitones', 'Semitones', -24, 24, 1);
 
 export const SoundFxPitch: SoundFxNodeDef = {
   type: 'SoundFxPitch',
@@ -99,10 +148,13 @@ export const SoundFxPitch: SoundFxNodeDef = {
   category: 'sound',
   description:
     'Plays the sound higher or lower, in semitones: 12 is an octave up. It is the speed the sound is played at, so a higher one is also shorter, and it applies to the whole sound wherever the node sits in the line.',
-  inputs: [audioIn],
+  inputs: [audioIn, numberIn(SEMITONES)],
   outputs: [audioOut],
-  params: [SEMITONES],
-  emit: (chain, params) => ({ ...chain, pitch: chain.pitch + read(params, SEMITONES) }),
+  params: [],
+  emit: (plan, amounts) => {
+    const semitones = held(amounts.semitones, SEMITONES);
+    return isNone(semitones) ? plan : { ...plan, pitch: [...plan.pitch, semitones] };
+  },
 };
 
 /** The five bands of the EQ: a shelf at either end and three peaks between them. */
@@ -116,7 +168,7 @@ export const EQ_BANDS: readonly { key: string; label: string; filter: FxFilter;
 
 /** About an octave and a half wide: neighbouring peaks overlap, so no frequency falls between them. */
 const PEAK_Q = 1;
-const EQ_PARAMS = EQ_BANDS.map((band) => numberParam(band.key, band.label, -24, 24, 0.5));
+const EQ_ROWS = EQ_BANDS.map((band) => numberRow(band.key, band.label, -24, 24, 0.5));
 
 export const SoundFxEq: SoundFxNodeDef = {
   type: 'SoundFxEq',
@@ -124,17 +176,17 @@ export const SoundFxEq: SoundFxNodeDef = {
   category: 'sound',
   description:
     'A five-band equalizer: raises or lowers the lows (80 Hz), low mids (250 Hz), mids (1 kHz), high mids (4 kHz) and highs (12 kHz), each in decibels. A band at 0 does nothing.',
-  inputs: [audioIn],
+  inputs: [audioIn, ...EQ_ROWS.map(numberIn)],
   outputs: [audioOut],
-  params: EQ_PARAMS,
-  emit: (chain, params) => {
-    const stages: FxStage[] = [];
+  params: [],
+  emit: (plan, amounts) => {
+    const stages: FxStagePlan[] = [];
     EQ_BANDS.forEach((band, i) => {
-      const gain = read(params, EQ_PARAMS[i]!);
-      if (gain !== 0)
+      const gain = held(amounts[band.key], EQ_ROWS[i]!);
+      if (!isNone(gain))
         stages.push({ kind: 'filter', filter: band.filter, frequency: band.frequency, gain, q: PEAK_Q });
     });
-    return stages.length === 0 ? chain : { ...chain, stages: [...chain.stages, ...stages] };
+    return stages.length === 0 ? plan : { ...plan, stages: [...plan.stages, ...stages] };
   },
 };
 
@@ -145,3 +197,26 @@ export const SOUND_FX_NODES: readonly SoundFxNodeDef[] = [
   SoundFxPitch,
   SoundFxEq,
 ];
+
+/** An amount with the value handed in for its parameter, held to its row; a 0 there does nothing. */
+function amountOf(amount: FxAmount, params: FxParams): number {
+  const given = amount.param !== undefined ? params[amount.param] : undefined;
+  if (given === undefined || !Number.isFinite(given)) return amount.value;
+  return Math.max(amount.min ?? -Infinity, Math.min(amount.max ?? Infinity, given));
+}
+
+/** The chain one voice is sent along: the plan with every parameter filled in. */
+export function fxChainOf(plan: FxPlan, params: FxParams = {}): FxChain {
+  const stages: FxStage[] = [];
+  for (const stage of plan.stages) {
+    if (stage.kind === 'gain') {
+      const db = amountOf(stage.db, params);
+      if (db !== 0) stages.push({ kind: 'gain', gain: 10 ** (db / 20) });
+      continue;
+    }
+    const gain = amountOf(stage.gain, params);
+    if (gain !== 0) stages.push({ ...stage, gain });
+  }
+  const pitch = plan.pitch.reduce((sum, amount) => sum + amountOf(amount, params), 0);
+  return { pitch, stages };
+}
diff --git a/src/core/store/serialize.ts b/src/core/store/serialize.ts
index 3c0d917a..b47e8782 100644
--- a/src/core/store/serialize.ts
+++ b/src/core/store/serialize.ts
@@ -487,6 +487,8 @@ function normalizePorts(raw: unknown, fixed: readonly string[], writable: boolea
     // A machine that is gone is kept, as a struct type is: the port then offers no states.
     if (kind === 'statemachine' && typeof p.machine === 'string' && p.machine !== '')
       port.machine = p.machine;
+    if (kind === 'number' && typeof p.default === 'number' && Number.isFinite(p.default))
+      port.default = p.default;
     ports.push(port);
   }
   return ports;
diff --git a/src/editor/debug/graphHooks.ts b/src/editor/debug/graphHooks.ts
index a99b9e31..2eeb026c 100644
--- a/src/editor/debug/graphHooks.ts
+++ b/src/editor/debug/graphHooks.ts
@@ -109,6 +109,9 @@ export function graphHooks({ state, editor }: HookContext) {
       }),
       playAt: () => centreOf(editor.soundFxEditor.playButton),
       stopAt: () => centreOf(editor.soundFxEditor.stopButton),
+      /** The header's parameter values, and setting one as its field would. */
+      params: () => editor.soundFxEditor.previewValues,
+      setParam: (key: string, value: number) => editor.soundFxEditor.setPreviewValue(key, value),
     },
     particles: {
       current: () => editor.particlesEditor.currentAssetId,
diff --git a/src/editor/graph/GraphCanvas.ts b/src/editor/graph/GraphCanvas.ts
index 960eb8e0..b4458ea5 100644
--- a/src/editor/graph/GraphCanvas.ts
+++ b/src/editor/graph/GraphCanvas.ts
@@ -22,6 +22,7 @@ import {
   RUN_BEHAVIOR,
   SHADER_CALL,
   callsFunction,
+  soundFxParamsMismatch,
   startStateOf,
 } from '../../core/graph';
 import type { GraphAsset } from '../../core/model/Asset';
@@ -325,6 +326,7 @@ export class GraphCanvas extends Widget {
       const problem =
         compilerProblems?.[node.id] ??
         (!compilerProblems || node.type === SHADER_CALL ? callProblem(node, lookup, asset.id) : null) ??
+        soundFxParamsMismatch(node, asset.graph) ??
         ghostProblem(node, asset.graph, resolved) ??
         blockProblem(asset.graph, node);
       view.sync(node, asset.graph, this.state.project, def, problem);
diff --git a/src/editor/graph/NodeView.ts b/src/editor/graph/NodeView.ts
index 38d6760a..dd066531 100644
--- a/src/editor/graph/NodeView.ts
+++ b/src/editor/graph/NodeView.ts
@@ -95,6 +95,8 @@ export function portColor(type: PortType): number {
       return c.portPicture;
     case 'audio':
       return c.portAudio;
+    case 'fxparams':
+      return c.portFxParams;
     case 'any':
       return c.portAny;
   }
diff --git a/src/editor/inspector/nodeSection.ts b/src/editor/inspector/nodeSection.ts
index 2b89c1df..6e13eb4e 100644
--- a/src/editor/inspector/nodeSection.ts
+++ b/src/editor/inspector/nodeSection.ts
@@ -1,6 +1,7 @@
 import {
   callProblem,
   declaresPropertyPorts,
+  declaresSoundFxPorts,
   declaresVariablePorts,
   edgesInto,
   edgesOfNode,
@@ -16,6 +17,8 @@ import {
   OBJECT_TYPE_PARAM,
   portSignature,
   resolveDef,
+  soundFxParamsMismatch,
+  soundFxSourceOf,
   STATE_TRANSITION,
   stateName,
   STRUCT_TYPE_PARAM,
@@ -42,6 +45,7 @@ import { addNote, addTitle, type InspectorHost } from './host';
 import {
   buildPortSection,
   buildPropertyPortSection,
+  buildSoundFxPortSection,
   buildVariablePortSection,
   variableChoices,
 } from './portSection';
@@ -67,7 +71,9 @@ export function nodeSignature(project: Project, assetId: string, nodeId: string)
   const declared = (node.ports ?? [])
     .map(
       (p) =>
-        `${p.key}:${p.kind}${p.write ? ':set' : ''}${p.machine ? `:${p.machine}:${machineOf(p.machine)}` : ''}`,
+        `${p.key}:${p.kind}${p.write ? ':set' : ''}${p.machine ? `:${p.machine}:${machineOf(p.machine)}` : ''}${
+          p.default !== undefined ? `=${p.default}` : ''
+        }`,
     )
     .join(',');
   // They decide which rows the inspector builds, and two behaviors may share a name in the title.
@@ -82,13 +88,13 @@ export function nodeSignature(project: Project, assetId: string, nodeId: string)
   // The source names which declarations the port menu offers, so switching it has to rebuild.
   const typeId = nodeStructType(node) || listNodeItemType(node);
   const typeName = structAssetOf(project, typeId)?.name ?? '';
-  const source = `${variablesSourceOf(node.params)}:${typeId}:${typeName}`;
+  const source = `${variablesSourceOf(node.params)}:${soundFxSourceOf(node.params)}:${typeId}:${typeName}`;
   const choices = variableChoices(project, assetId, node)
     .map((v) => v.key)
     .join(',');
   return `${portSignature(node, asset.graph, lookup, assetId)}|${declared}|${connected.join(
     ',',
-  )}|${source}:${choices}|${target}|${transitions}`;
+  )}|${source}:${choices}|${target}|${transitions}|${soundFxParamsMismatch(node, asset.graph) ?? ''}`;
 }
 
 /** The name of the state at the other end of an edge – what a transition row is labelled with. */
@@ -111,7 +117,8 @@ export function buildNodeSection(host: InspectorHost, assetId: string, nodeId: s
   addTitle(host, `${def.category.toUpperCase()} NODE`);
   host.body.add(new Label(def.label, { style: 'bodyBold' }));
   addNote(host, def.description);
-  const problem = callProblem(node, graphLookup(host.state.project), assetId);
+  const problem =
+    callProblem(node, graphLookup(host.state.project), assetId) ?? soundFxParamsMismatch(node, asset.graph);
   if (problem) addNote(host, problem, 'warning');
   const addSetting = (param: PropertyDef, handlers = paramHandlers(host, assetId, nodeId, param)) => {
     const row = createFieldRow(host, param, node.params[param.key] ?? param.default, handlers);
@@ -119,7 +126,8 @@ export function buildNodeSection(host: InspectorHost, assetId: string, nodeId: s
     host.body.add(row.row);
   };
   // Both draw their settings inside the port section: a setting decides what the menu offers.
-  const ownSettings = declaresPropertyPorts(node.type) || declaresVariablePorts(node.type);
+  const ownSettings =
+    declaresPropertyPorts(node.type) || declaresVariablePorts(node.type) || declaresSoundFxPorts(node.type);
   // The type of a Pack/Expand decides its fields (#253), so it stands above them – and picking one
   // rewrites the ports, which a plain param edit would not.
   const typed = isTypedNode(node);
@@ -134,6 +142,7 @@ export function buildNodeSection(host: InspectorHost, assetId: string, nodeId: s
   const pickItemType = (value: PropertyValue) =>
     host.state.execute(new SetListNodeTypeCommand(assetId, nodeId, textOf(value)));
   if (declaresVariablePorts(node.type)) buildVariablePortSection(host, assetId, node, addSetting);
+  else if (declaresSoundFxPorts(node.type)) buildSoundFxPortSection(host, assetId, node, addSetting);
   else if (ownSettings) buildPropertyPortSection(host, assetId, node, addSetting);
   else if (def.declaresPorts) {
     const typeName = structAssetOf(host.state.project, nodeStructType(node))?.name ?? null;
diff --git a/src/editor/inspector/portSection.ts b/src/editor/inspector/portSection.ts
index 6782f285..922c5c74 100644
--- a/src/editor/inspector/portSection.ts
+++ b/src/editor/inspector/portSection.ts
@@ -6,12 +6,14 @@ import {
   RemovePortCommand,
   RenamePortCommand,
   RepointPortCommand,
+  SetPortDefaultCommand,
   SetPortMachineCommand,
   SetPortWriteCommand,
 } from '../../core/commands/portCommands';
 import {
   type DeclaredPort,
   type GraphNode,
+  declaresSoundFxPorts,
   isEntryTerminal,
   isPortOf,
   isTerminalNode,
@@ -23,6 +25,10 @@ import {
   portKindOf,
   SHADER_FUNCTION_INPUT,
   SHADER_FUNCTION_OUTPUT,
+  SOUND_FX_INPUT,
+  SOUND_FX_SETTING,
+  soundFxSourceOf,
+  terminalNode,
   VARIABLES_SETTING,
   variablesSourceOf,
   propertyTargetOf,
@@ -44,6 +50,7 @@ import {
   Label,
   Menu,
   type MenuItem,
+  NumberField,
   type SectionHeader,
   type SortBlock,
   sortBlocks,
@@ -58,6 +65,7 @@ import { kindMenu, markLabel } from './variableRows';
 
 /** Whose declarations a Variables node picks its ports from: the asset it names, else the behavior. */
 export function variableChoices(project: Project, assetId: string, node: GraphNode): PropertyDef[] {
+  if (declaresSoundFxPorts(node.type)) return soundFxChoices(project, node);
   const source = variablesSourceOf(node.params);
   if (source) return findAssetOf(project, source, 'variables')?.variables ?? [];
   const asset = findGraphAsset(project, assetId);
@@ -90,6 +98,35 @@ export function buildVariablePortSection(
   });
 }
 
+/** The parameters the Input of the sound FX a `Sound FX parameters` node names declares (#311). */
+function soundFxChoices(project: Project, node: GraphNode): PropertyDef[] {
+  const fx = findAssetOf(project, soundFxSourceOf(node.params), 'soundfx');
+  const ports = fx ? (terminalNode(fx.graph, SOUND_FX_INPUT)?.ports ?? []) : [];
+  return ports.map((p) => ({ key: p.key, label: p.key, kind: 'number', default: p.default ?? 0 }));
+}
+
+/** The ports of a `Sound FX parameters` node: picked from the parameters of the FX it names. */
+export function buildSoundFxPortSection(
+  host: InspectorHost,
+  assetId: string,
+  node: GraphNode,
+  addSetting: (def: PropertyDef) => void,
+): void {
+  addSetting(SOUND_FX_SETTING);
+  const id = soundFxSourceOf(node.params);
+  const fx = id ? findAssetOf(host.state.project, id, 'soundfx') : undefined;
+  buildPickedPortSection(host, assetId, node, {
+    noun: 'Parameter',
+    choices: soundFxChoices(host.state.project, node),
+    owner: fx ? `"${fx.name}"` : 'a sound FX',
+    empty: id
+      ? fx
+        ? `"${fx.name}" declares no parameters yet. Add them at its Input.`
+        : 'That sound FX is gone.'
+      : 'Pick a sound FX first.',
+  });
+}
+
 /** The type decides what the ports are picked from; Any names them by hand, with a kind picked. */
 export function buildPropertyPortSection(
   host: InspectorHost,
@@ -133,7 +170,7 @@ export function buildPropertyPortSection(
 }
 
 interface PickedPorts {
-  noun: 'Variable' | 'Property';
+  noun: 'Variable' | 'Property' | 'Parameter';
   choices: readonly PropertyDef[];
   /** Whose ports these are, for the warning on one it does not have. */
   owner: string;
@@ -153,7 +190,7 @@ function buildPickedPortSection(
   { noun, choices, owner, empty, custom = false, note, hidden }: PickedPorts,
 ): void {
   const offered = hidden ? choices.filter((def) => !hidden(def)) : choices;
-  const plural = noun === 'Property' ? 'properties' : 'variables';
+  const plural = noun === 'Property' ? 'properties' : noun === 'Parameter' ? 'parameters' : 'variables';
   const ports = node.ports ?? [];
   const taken = new Set(ports.map((p) => p.key));
   const portOf = (def: PropertyDef): DeclaredPort => ({ key: def.key, kind: portKindOf(def) });
@@ -191,9 +228,10 @@ function buildPickedPortSection(
   const pickedRow = (port: DeclaredPort): Grip => {
     // A machine a variable holds is a running value; which one its states come from is picked here.
     const carries = noun === 'Variable' && port.kind === 'statemachine';
+    // A parameter is only ever handed in, never written back.
     const toggle = [
       ...(carries ? [machinePick(host, assetId, node, port)] : []),
-      ...writeToggle(host, assetId, node, port),
+      ...(noun === 'Parameter' ? [] : writeToggle(host, assetId, node, port)),
     ];
     if (custom)
       return portRow(host, assetId, node, port, portNameField(host, assetId, node, port), toggle).grip;
@@ -238,9 +276,10 @@ export function buildPortSection(
   typeName: string | null = null,
 ): void {
   const onStart = isEntryTerminal(node.type);
-  const noun = isTerminalNode(node) ? (onStart ? 'Input' : 'Output') : 'Field';
+  const ofSoundFx = node.type === SOUND_FX_INPUT;
+  const noun = ofSoundFx ? 'Parameter' : isTerminalNode(node) ? (onStart ? 'Input' : 'Output') : 'Field';
   const ofFunction = node.type === SHADER_FUNCTION_INPUT || node.type === SHADER_FUNCTION_OUTPUT;
-  const base = noun === 'Field' ? 'field' : onStart ? 'in' : 'out';
+  const base = ofSoundFx ? 'param' : noun === 'Field' ? 'field' : onStart ? 'in' : 'out';
 
   const header = sectionHeader(host, `${noun.toUpperCase()}S`);
   // With a Struct asset as its type the fields are that asset's (#253): changed there, not here.
@@ -277,11 +316,13 @@ export function buildPortSection(
       host,
       noun === 'Field'
         ? 'No fields yet. Every field added here becomes a port of the struct.'
-        : ofFunction
-          ? `No ${plural(noun)} yet. Every ${noun.toLowerCase()} added here, a number or a color, becomes a port on the nodes calling this function.`
-          : onStart
-            ? 'No inputs yet. Every input added here becomes a port on the node that runs this behavior; one of the kind Flow is a further way in.'
-            : 'No outputs yet. Every output added here becomes a result of running this behavior; one of the kind Flow is a further way out.',
+        : ofSoundFx
+          ? 'No parameters yet. Every parameter added here is a number with a default, and a Sound FX parameters node can set it when the sound is played.'
+          : ofFunction
+            ? `No ${plural(noun)} yet. Every ${noun.toLowerCase()} added here, a number or a color, becomes a port on the nodes calling this function.`
+            : onStart
+              ? 'No inputs yet. Every input added here becomes a port on the node that runs this behavior; one of the kind Flow is a further way in.'
+              : 'No outputs yet. Every output added here becomes a result of running this behavior; one of the kind Flow is a further way out.',
     );
 
   const blocks = ports.map((port) =>
@@ -291,13 +332,18 @@ export function buildPortSection(
       node,
       port,
       portNameField(host, assetId, node, port),
-      onStart && port.kind === 'statemachine' ? [machinePick(host, assetId, node, port)] : [],
+      ofSoundFx
+        ? defaultField(host, assetId, node, port)
+        : onStart && port.kind === 'statemachine'
+          ? [machinePick(host, assetId, node, port)]
+          : [],
     ),
   );
   sortBlocks(blocks, (from, to) => host.state.execute(new MovePortCommand(assetId, node.id, from, to)));
 }
 
 const plural = (noun: string) => `${noun.toLowerCase()}s`;
+const DEFAULT_WIDTH = 56;
 
 function portNameField(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): TextField {
   return new TextField(port.key, {
@@ -332,6 +378,19 @@ function machinePick(host: InspectorHost, assetId: string, node: GraphNode, port
   return pick;
 }
 
+/** The value a sound FX parameter has where nobody hands one in. */
+function defaultField(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): Widget[] {
+  const field = new NumberField(port.default ?? 0, {
+    width: DEFAULT_WIDTH,
+    step: 0.1,
+    onChange: (value) => {
+      if (value !== (port.default ?? 0))
+        host.state.execute(new SetPortDefaultCommand(assetId, node.id, port.key, value));
+    },
+  });
+  return [new Label('Default', { style: 'muted' }), field];
+}
+
 function writeToggle(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): Widget[] {
   const box = new Checkbox(port.write === true);
   box.onChange = (on) => host.state.execute(new SetPortWriteCommand(assetId, node.id, port.key, on));
diff --git a/src/editor/soundfx/SoundFxEditor.ts b/src/editor/soundfx/SoundFxEditor.ts
index e1ee326a..20259b93 100644
--- a/src/editor/soundfx/SoundFxEditor.ts
+++ b/src/editor/soundfx/SoundFxEditor.ts
@@ -2,8 +2,9 @@ import type { Asset, SoundFxAsset } from '../../core/model/Asset';
 import { findAssetOf } from '../../core/model/Project';
 import { resolveAssetProps } from '../../core/properties/resolve';
 import { volumeOf } from '../../core/properties/sounds';
-import { soundFxBuildFor } from '../../core/soundfx/compile';
-import { Button, Dropdown, Menu } from '../../ui';
+import { soundFxBuildFor, soundFxParams } from '../../core/soundfx/compile';
+import { fxChainOf } from '../../core/soundfx/nodes';
+import { Button, Dropdown, HStack, Label, Menu, NumberField, Stack, Theme } from '../../ui';
 import { soundLibrary } from '../../viewport/SoundLibrary';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
@@ -14,6 +15,7 @@ import type { EditorState } from '../state';
 /** Room kept for "N effects", or for the reason the graph does not compile. */
 const INFO_WIDTH = 220;
 const SOUND_WIDTH = 140;
+const PARAM_WIDTH = 48;
 /** Whose voices the tab's Stop silences: its own, never a running game's. */
 const PREVIEW_OWNER = 'soundfx-preview';
 
@@ -29,6 +31,15 @@ export class SoundFxEditor extends AssetTabEditor<SoundFxAsset, GraphCanvas> {
   readonly playButton: Button;
   readonly stopButton: Button;
   private soundId = '';
+  /** One name and number per parameter of the Input: what the header's Play hands in. */
+  private readonly paramBar = new HStack({ gap: Theme.gap, align: 'center' });
+  private readonly paramFields = new Map<string, NumberField>();
+  /** The values the tab plays with – its own, never written into the asset. */
+  private values: Record<string, number> = {};
+  /** The defaults the values were taken from, so an edited default comes through and a moved value stays. */
+  private defaults: Record<string, number> = {};
+  private paramsKey = '';
+  private valuesFor = '';
 
   constructor(state: EditorState) {
     super(state, { infoWidth: INFO_WIDTH });
@@ -43,9 +54,11 @@ export class SoundFxEditor extends AssetTabEditor<SoundFxAsset, GraphCanvas> {
       this.soundPicker,
       this.playButton,
       this.stopButton,
+      this.paramBar,
     ]);
     state.on('load', () => {
       this.soundId = '';
+      this.valuesFor = '';
     });
   }
 
@@ -68,14 +81,26 @@ export class SoundFxEditor extends AssetTabEditor<SoundFxAsset, GraphCanvas> {
     this.refresh();
   }
 
+  /** What the header's parameter fields are set to – the check scripts read this. */
+  get previewValues(): Record<string, number> {
+    return { ...this.values };
+  }
+
+  /** Sets one parameter the header plays with, as typing into its field does. */
+  setPreviewValue(key: string, value: number): void {
+    if (!(key in this.values)) return;
+    this.values[key] = value;
+    this.paramFields.get(key)?.setNumber(value);
+  }
+
   /** Plays the picked sound through the graph; a graph that does not compile is not played at all. */
   play(): void {
     const asset = this.asset();
     const sound = findAssetOf(this.state.project, this.previewSoundId, 'sound');
-    const chain = asset && soundFxBuildFor(asset).compiled;
-    if (!sound?.file || !chain) return;
+    const plan = asset && soundFxBuildFor(asset).compiled;
+    if (!sound?.file || !plan) return;
     const volume = volumeOf(resolveAssetProps(this.state.project, sound));
-    soundLibrary.play(sound.file, volume, false, PREVIEW_OWNER, chain);
+    soundLibrary.play(sound.file, volume, false, PREVIEW_OWNER, fxChainOf(plan, this.values));
   }
 
   stop(): void {
@@ -95,6 +120,48 @@ export class SoundFxEditor extends AssetTabEditor<SoundFxAsset, GraphCanvas> {
     this.soundPicker.setEnabled(Boolean(asset && sound));
     this.playButton.setEnabled(Boolean(asset && sound?.file && soundFxBuildFor(asset).compiled));
     this.stopButton.setEnabled(Boolean(asset));
+    this.syncParams(asset);
+  }
+
+  /**
+   * Another asset starts from its defaults; an edit of the graph keeps what a field was moved to,
+   * unless that parameter's default changed with it.
+   */
+  private syncParams(asset: SoundFxAsset | null): void {
+    const params = asset ? soundFxParams(asset.graph) : [];
+    const same = (asset?.id ?? '') === this.valuesFor;
+    this.valuesFor = asset?.id ?? '';
+    const values: Record<string, number> = {};
+    const defaults: Record<string, number> = {};
+    for (const port of params) {
+      const fallback = port.default ?? 0;
+      const kept = same && this.defaults[port.key] === fallback ? this.values[port.key] : undefined;
+      values[port.key] = kept ?? fallback;
+      defaults[port.key] = fallback;
+    }
+    this.values = values;
+    this.defaults = defaults;
+
+    const key = params.map((p) => p.key).join('\u0000');
+    if (key !== this.paramsKey) {
+      this.paramsKey = key;
+      for (const child of this.paramBar.removeChildren()) child.destroy({ children: true });
+      this.paramFields.clear();
+      for (const port of params) {
+        this.paramBar.add(new Label(port.key, { style: 'small' }));
+        const field = new NumberField(values[port.key], {
+          width: PARAM_WIDTH,
+          step: 0.1,
+          onInput: (value) => (this.values[port.key] = value),
+          onChange: (value) => (this.values[port.key] = value),
+        });
+        this.paramFields.set(port.key, field);
+        this.paramBar.add(field);
+      }
+      if (this.paramBar.parent instanceof Stack) this.paramBar.parent.relayout();
+      this.paramBar.relayout();
+    }
+    for (const [name, field] of this.paramFields) field.setNumber(this.values[name] ?? 0);
   }
 
   private openSoundPicker(): void {
diff --git a/src/runtime/systems/behaviorContext.ts b/src/runtime/systems/behaviorContext.ts
index 0abcb034..0cfa19ab 100644
--- a/src/runtime/systems/behaviorContext.ts
+++ b/src/runtime/systems/behaviorContext.ts
@@ -16,7 +16,7 @@ import { hasRenderLayer } from '../../core/properties/PropertySchema';
 import { resolveAssetProps } from '../../core/properties/resolve';
 import { loopsOf, volumeOf } from '../../core/properties/sounds';
 import { soundFxBuildFor } from '../../core/soundfx/compile';
-import { DRY } from '../../core/soundfx/nodes';
+import { DRY, fxChainOf, type FxParams } from '../../core/soundfx/nodes';
 import type { Entity } from '../Entity';
 import { PhysicsSystem } from '../physics/PhysicsSystem';
 import type { World } from '../World';
@@ -164,8 +164,8 @@ export function behaviorContext(
       // eslint-disable-next-line no-console
       console.log(`[behavior ${entity.name}]`, message);
     },
-    playSound: (assetId, volume, loop, detached, fx) =>
-      playSound(run, assetId, volume, loop, detached ? '' : entity.id, fx),
+    playSound: (assetId, volume, loop, detached, fx, fxParams) =>
+      playSound(run, assetId, volume, loop, detached ? '' : entity.id, fx, fxParams),
     // An id nothing resolves stops nothing, rather than silencing the whole run by accident;
     // only the empty id means "everything", which is what the node promises.
     stopSound: (assetId) => {
@@ -217,7 +217,8 @@ export function behaviorContext(
  * What the graph asked for, as the sink understands it: the asset's own volume scaled by the
  * node's, and its loop flag unless the node overrules it either way. The asset is what a sound
  * *is* – a node that says nothing therefore plays it as the project describes it. An FX asset that
- * does not compile plays the sound dry: a broken effect should not silence the game.
+ * does not compile plays the sound dry: a broken effect should not silence the game. Its parameters
+ * take the values handed in, the others their defaults.
  */
 function playSound(
   { project, audio }: ContextSources,
@@ -226,13 +227,15 @@ function playSound(
   loop: boolean | undefined,
   owner: string,
   fxId: string,
+  fxParams: FxParams,
 ): void {
   const asset = findAssetOf(project, assetId, 'sound');
   if (!asset?.file) return;
   const props = resolveAssetProps(project, asset);
   const level = Math.max(0, Math.min(1, volumeOf(props) * volume));
   const fx = fxId ? findAssetOf(project, fxId, 'soundfx') : undefined;
-  audio.play(asset.file, level, loop ?? loopsOf(props), owner, (fx && soundFxBuildFor(fx).compiled) || DRY);
+  const plan = fx && soundFxBuildFor(fx).compiled;
+  audio.play(asset.file, level, loop ?? loopsOf(props), owner, plan ? fxChainOf(plan, fxParams) : DRY);
 }
 
 /** Where a ray of that length ends; where it has no direction, where it starts. */
diff --git a/src/ui/Theme.ts b/src/ui/Theme.ts
index 9d0a2580..a3d939a9 100644
--- a/src/ui/Theme.ts
+++ b/src/ui/Theme.ts
@@ -80,6 +80,7 @@ export const Theme = {
     portVec3: 0xff9ad5,
     portPicture: 0x9b8cff,
     portAudio: 0xf0c060,
+    portFxParams: 0xd0629b,
     portAny: 0xbdbdbd,
     /** Ring around the port a running edge drag would connect to. */
     portTarget: 0xffffff,
diff --git a/tests/core/node-catalog.test.ts b/tests/core/node-catalog.test.ts
index 845b36a8..9506d378 100644
--- a/tests/core/node-catalog.test.ts
+++ b/tests/core/node-catalog.test.ts
@@ -1950,7 +1950,9 @@ const CASES: Record<string, Case[]> = {
       // flag – is the BehaviorSystem's to resolve, since only it holds the project (see
       // `sounds.test.ts`).
       after: (ctx) =>
-        expect(ctx.played).toEqual([{ assetId: 'snd-1', volume: 0.5, loop: true, detached: false, fx: '' }]),
+        expect(ctx.played).toEqual([
+          { assetId: 'snd-1', volume: 0.5, loop: true, detached: false, fx: '', fxParams: {} },
+        ]),
     },
     {
       name: 'detached says the voice is nobody’s, so destroying this object leaves it playing',
@@ -1976,6 +1978,24 @@ const CASES: Record<string, Case[]> = {
       next: 'exec',
       after: (ctx) => expect(ctx.played[0]?.fx).toBe('fx-1'),
     },
+    {
+      name: 'hands on the numbers of its fx params, and nothing for what is no bundle',
+      inputs: { sound: 'snd-1', volume: 1, loop: '', fx: 'fx-1', fxParams: { depth: -12, name: 'x' } },
+      next: 'exec',
+      after: (ctx) => expect(ctx.played[0]?.fxParams).toEqual({ depth: -12 }),
+    },
+  ],
+  SoundFxParameters: [
+    {
+      name: 'bundles its picked parameters as numbers',
+      ports: [
+        { key: 'depth', kind: 'number' },
+        { key: 'loud', kind: 'number' },
+      ],
+      inputs: { depth: '-12', loud: 3 },
+      outputs: { params: { depth: -12, loud: 3 } },
+    },
+    { name: 'with none picked the bundle is empty', outputs: { params: {} } },
   ],
   LoadScene: [
     {
diff --git a/tests/core/soundfx.test.ts b/tests/core/soundfx.test.ts
index f84ac396..3a59d9c1 100644
--- a/tests/core/soundfx.test.ts
+++ b/tests/core/soundfx.test.ts
@@ -4,12 +4,15 @@
  */
 import { describe, expect, it } from 'vitest';
 import { buildAsset, CreateAssetCommand, CreateSoundCommand } from '../../src/core/commands/assetCommands';
-import { portsCompatible } from '../../src/core/graph/Graph';
+import { RenamePortCommand, SetPortDefaultCommand } from '../../src/core/commands/portCommands';
+import { callProblem, resolveDef, soundFxParamsMismatch } from '../../src/core/graph';
+import { type DeclaredPort, portsCompatible } from '../../src/core/graph/Graph';
+import { graphLookup } from '../../src/core/model/graphLookup';
 import type { BehaviorAsset, SoundFxAsset } from '../../src/core/model/Asset';
 import { isPlaceableType } from '../../src/core/model/AssetTypes';
 import { assetRefChoices } from '../../src/core/properties/assetRef';
 import { compileSoundFx, soundFxBuildFor } from '../../src/core/soundfx/compile';
-import { DRY, type FxChain } from '../../src/core/soundfx/nodes';
+import { DRY, EMPTY_PLAN, type FxChain, fxChainOf } from '../../src/core/soundfx/nodes';
 import { deserializeProject } from '../../src/core/store/serialize';
 import type { AudioSink } from '../../src/runtime/systems/Audio';
 import { paletteEntries } from '../../src/editor/graph/paletteEntries';
@@ -116,7 +119,8 @@ describe('compiling a sound FX graph', () => {
 
   it('passes the sound on untouched through Input and Output alone', () => {
     const build = compileSoundFx(line([]).fx.graph);
-    expect(build).toMatchObject({ compiled: DRY, effects: 0, reason: '' });
+    expect(build).toMatchObject({ compiled: EMPTY_PLAN, effects: 0, reason: '' });
+    expect(fxChainOf(build.compiled!)).toEqual(DRY);
   });
 
   it('turns every node on the line into its stages, in order', () => {
@@ -128,7 +132,7 @@ describe('compiling a sound FX graph', () => {
     ]);
     const build = compileSoundFx(f.fx.graph);
     expect(build.effects).toBe(4);
-    const chain = build.compiled!;
+    const chain = fxChainOf(build.compiled!);
     expect(chain.pitch).toBe(7);
     expect(chain.stages).toHaveLength(3);
     expect(chain.stages[0]!.kind).toBe('gain');
@@ -141,10 +145,12 @@ describe('compiling a sound FX graph', () => {
 
   it('leaves out what does nothing and holds a value to its row', () => {
     const quiet = compileSoundFx(line([{ type: 'SoundFxGain' }, { type: 'SoundFxEq' }]).fx.graph);
-    expect(quiet.compiled).toEqual(DRY);
+    expect(quiet.compiled).toEqual(EMPTY_PLAN);
     expect(quiet.effects).toBe(2);
 
-    const loud = compileSoundFx(line([{ type: 'SoundFxGain', params: { gain: 200 } }]).fx.graph).compiled!;
+    const loud = fxChainOf(
+      compileSoundFx(line([{ type: 'SoundFxGain', params: { gain: 200 } }]).fx.graph).compiled!,
+    );
     expect(loud.stages[0]!.gain).toBeCloseTo(10 ** (24 / 20));
   });
 
@@ -153,7 +159,7 @@ describe('compiling a sound FX graph', () => {
     const aside = f.edit.addNode('SoundFxGain', { gain: -20 });
     f.edit.connect(f.input, 'out', aside, 'in');
     const build = compileSoundFx(f.fx.graph);
-    expect(build.compiled).toEqual({ pitch: 3, stages: [] });
+    expect(fxChainOf(build.compiled!)).toEqual({ pitch: 3, stages: [] });
     expect(build.effects).toBe(1);
   });
 });
@@ -217,3 +223,176 @@ describe('Play sound with fx', () => {
     for (const audio of [none, gone, brokenAudio]) expect(audio.played).toEqual([{ file: FILE, fx: DRY }]);
   });
 });
+
+/** Input with the given parameters, its `param` fed into the effect's `into`, then Output. */
+function withParam(type: string, into: string, ports: DeclaredPort[], param = ports[0]!.key) {
+  const f = line([{ type }]);
+  f.input.ports = ports;
+  const effect = f.fx.graph.nodes.find((n) => n.type === type)!;
+  f.edit.connect(f.input, param, effect, into);
+  return f;
+}
+
+describe('the parameters of a sound FX', () => {
+  it('stay open in the plan and take the value handed in, held to the row', () => {
+    const f = withParam('SoundFxPitch', 'semitones', [{ key: 'depth', kind: 'number', default: -12 }]);
+    const plan = soundFxBuildFor(f.fx).compiled!;
+    expect(plan.pitch).toEqual([{ value: -12, param: 'depth', min: -24, max: 24 }]);
+    expect(fxChainOf(plan).pitch).toBe(-12);
+    expect(fxChainOf(plan, { depth: 5 }).pitch).toBe(5);
+    expect(fxChainOf(plan, { depth: 100 }).pitch).toBe(24);
+    expect(fxChainOf(plan, { other: 3 }).pitch).toBe(-12);
+  });
+
+  it('keep a stage that is 0 by default, so a value handed in can open it', () => {
+    const f = withParam('SoundFxGain', 'gain', [{ key: 'loud', kind: 'number' }]);
+    const plan = soundFxBuildFor(f.fx).compiled!;
+    expect(plan.stages).toHaveLength(1);
+    expect(fxChainOf(plan)).toEqual(DRY);
+    expect(fxChainOf(plan, { loud: 6 }).stages[0]).toMatchObject({ kind: 'gain' });
+    expect((fxChainOf(plan, { loud: 6 }).stages[0] as { gain: number }).gain).toBeCloseTo(10 ** (6 / 20));
+  });
+
+  it('feed an EQ band as well', () => {
+    const f = withParam('SoundFxEq', 'mid', [{ key: 'body', kind: 'number', default: 3 }]);
+    const chain = fxChainOf(soundFxBuildFor(f.fx).compiled!, { body: -4 });
+    expect(chain.stages).toEqual([{ kind: 'filter', filter: 'peaking', frequency: 1000, gain: -4, q: 1 }]);
+  });
+
+  it('are kept with their defaults through a save, a default only on a number', () => {
+    const f = withParam('SoundFxPitch', 'semitones', [{ key: 'depth', kind: 'number', default: -7 }]);
+    expect(roundTrip(f.project)).toEqual(f.project);
+    const loaded = deserializeProject({
+      name: 'P',
+      assets: [
+        {
+          id: 'fx',
+          type: 'soundfx',
+          name: 'FX',
+          graph: {
+            nodes: [
+              {
+                id: 'a',
+                type: 'SoundFxInput',
+                x: 0,
+                y: 0,
+                params: {},
+                ports: [
+                  { key: 'p', kind: 'number', default: 'loud' },
+                  { key: 'q', kind: 'number', default: 2 },
+                ],
+              },
+            ],
+            edges: [],
+          },
+        },
+      ],
+    });
+    expect((loaded.assets[0] as SoundFxAsset).graph.nodes[0]!.ports).toEqual([
+      { key: 'p', kind: 'number' },
+      { key: 'q', kind: 'number', default: 2 },
+    ]);
+  });
+
+  it('do not go where a sound goes, and a sound does not go where a number does', () => {
+    const f = line([{ type: 'SoundFxGain' }]);
+    f.input.ports = [{ key: 'level', kind: 'number' }];
+    const gain = f.fx.graph.nodes.find((n) => n.type === 'SoundFxGain')!;
+    f.fx.graph.edges.find((e) => e.to.node === gain.id)!.from.port = 'level';
+    expect(compileSoundFx(f.fx.graph).problems[gain.id]).toBe('"in" takes a sound');
+    expect(portsCompatible('fxparams', 'fxparams')).toBe(true);
+    expect(portsCompatible('fxparams', 'any')).toBe(false);
+    expect(portsCompatible('struct', 'fxparams')).toBe(false);
+  });
+
+  it('have a default set by a command that undoes', () => {
+    const f = withParam('SoundFxPitch', 'semitones', [{ key: 'depth', kind: 'number' }]);
+    f.stack.execute(new SetPortDefaultCommand(f.fx.id, f.input.id, 'depth', 4));
+    expect(f.input.ports).toEqual([{ key: 'depth', kind: 'number', default: 4 }]);
+    expect(fxChainOf(soundFxBuildFor(f.fx).compiled!).pitch).toBe(4);
+    f.stack.undo();
+    expect(f.input.ports).toEqual([{ key: 'depth', kind: 'number' }]);
+  });
+});
+
+describe('Sound FX parameters and Play sound', () => {
+  function scene(options: { pick?: string[]; values?: Record<string, number>; other?: boolean } = {}) {
+    const f = makeSpriteScene('Box');
+    const withFx = makeFx(f);
+    const { fx, edit: fxEdit } = withFx;
+    const input = fxEdit.addNode('SoundFxInput');
+    input.ports = [
+      { key: 'depth', kind: 'number', default: -12 },
+      { key: 'loud', kind: 'number', default: 0 },
+    ];
+    const pitch = fxEdit.addNode('SoundFxPitch');
+    const gain = fxEdit.addNode('SoundFxGain');
+    const output = fxEdit.addNode('SoundFxOutput');
+    fxEdit.connect(input, 'out', pitch, 'in');
+    fxEdit.connect(pitch, 'out', gain, 'in');
+    fxEdit.connect(gain, 'out', output, 'in');
+    fxEdit.connect(input, 'depth', pitch, 'semitones');
+    fxEdit.connect(input, 'loud', gain, 'gain');
+    const sound = new CreateSoundCommand('Jump', FILE);
+    f.stack.execute(sound);
+    const behavior = makeBehavior(f, 'Logic');
+    place(f, behavior.id, { x: 0, y: 0 }, place(f, f.spriteId, { x: 0, y: 0 }));
+    const edit = graphEditor(f, behavior);
+    const start = edit.addNode('OnStart');
+    const play = edit.addNode('PlaySound', { sound: sound.asset.id, fx: fx.id });
+    const named = options.other ? 'another-fx' : fx.id;
+    const params = edit.addNode('SoundFxParameters', { soundFxAsset: named, ...options.values });
+    params.ports = (options.pick ?? []).map((key) => ({ key, kind: 'number' as const }));
+    edit.connect(start, 'exec', play, 'exec');
+    edit.connect(params, 'params', play, 'fxParams');
+    return { ...f, fx, input, behavior, play, params };
+  }
+
+  it('hands the picked values to the voice, the others keep their defaults', () => {
+    const f = scene({ pick: ['depth'], values: { depth: 7 } });
+    const audio = fakeAudio();
+    startWorld(f, { behaviors: true, audio }).frame();
+    expect(audio.played).toEqual([{ file: FILE, fx: { pitch: 7, stages: [] } }]);
+  });
+
+  it('starts a picked parameter at the default of the FX', () => {
+    const f = scene({ pick: ['depth', 'loud'] });
+    const def = resolveDef(f.params, f.behavior.graph, graphLookup(f.project))!;
+    expect(def.inputs.map((p) => [p.key, p.default])).toEqual([
+      ['depth', -12],
+      ['loud', 0],
+    ]);
+    const audio = fakeAudio();
+    startWorld(f, { behaviors: true, audio }).frame();
+    expect(audio.played[0]!.fx).toEqual({ pitch: -12, stages: [] });
+  });
+
+  it('says so at the node when no FX is picked or it is gone', () => {
+    const f = scene();
+    const lookup = graphLookup(f.project);
+    expect(callProblem(f.params, lookup)).toBeNull();
+    f.params.params.soundFxAsset = '';
+    expect(callProblem(f.params, lookup)).toBe('No sound FX picked');
+    f.params.params.soundFxAsset = 'gone';
+    expect(callProblem(f.params, lookup)).toBe('That sound FX is gone');
+  });
+
+  it('warns at Play sound when the parameters are for another FX', () => {
+    expect(soundFxParamsMismatch(scene().play, scene().behavior.graph)).toBeNull();
+    const f = scene({ other: true });
+    expect(soundFxParamsMismatch(f.play, f.behavior.graph)).toBe('The parameters are for another sound FX');
+  });
+
+  it('follow a parameter renamed at the Input, edges and value included, and back on undo', () => {
+    const f = scene({ pick: ['depth'], values: { depth: 7 } });
+    f.stack.execute(new RenamePortCommand(f.fx.id, f.input.id, 'depth', 'drop'));
+    expect(f.params.ports).toEqual([{ key: 'drop', kind: 'number' }]);
+    expect(f.params.params.drop).toBe(7);
+    const audio = fakeAudio();
+    startWorld(f, { behaviors: true, audio }).frame();
+    expect(audio.played[0]!.fx).toEqual({ pitch: 7, stages: [] });
+    f.stack.undo();
+    expect(f.params.ports).toEqual([{ key: 'depth', kind: 'number' }]);
+    expect(f.params.params.depth).toBe(7);
+  });
+});
diff --git a/tests/helpers.ts b/tests/helpers.ts
index 89450b39..b376e514 100644
--- a/tests/helpers.ts
+++ b/tests/helpers.ts
@@ -205,7 +205,14 @@ export type FakeContext = NodeContext & {
   stopped: boolean;
   changes: { machineId: string; from: string; to: string }[];
   /** What the context was asked to play and to silence, in order – nothing here makes a noise. */
-  played: { assetId: string; volume: number; loop: boolean | undefined; detached: boolean; fx: string }[];
+  played: {
+    assetId: string;
+    volume: number;
+    loop: boolean | undefined;
+    detached: boolean;
+    fx: string;
+    fxParams: Readonly<Record<string, number>>;
+  }[];
   silenced: string[];
   /** The scenes the context was asked to load, in order. */
   loaded: string[];
@@ -258,8 +265,8 @@ export function fakeContext(overrides: Partial<NodeContext> = {}): FakeContext {
     played: [],
     silenced: [],
     loaded: [],
-    playSound: (assetId, volume, loop, detached, fx) =>
-      ctx.played.push({ assetId, volume, loop, detached, fx }),
+    playSound: (assetId, volume, loop, detached, fx, fxParams) =>
+      ctx.played.push({ assetId, volume, loop, detached, fx, fxParams }),
     stopSound: (assetId) => ctx.silenced.push(assetId),
     loadScene: (sceneId) => ctx.loaded.push(sceneId),
     spawn: () => null,
diff --git a/tools/e2e/34-sound.mjs b/tools/e2e/34-sound.mjs
index 3e226280..03168487 100644
--- a/tools/e2e/34-sound.mjs
+++ b/tools/e2e/34-sound.mjs
@@ -272,7 +272,9 @@ export async function sound(t) {
 
   // 34g-3. A sound FX asset (#311): "+ → Sound FX" opens its tab, which says what keeps the graph
   //        from compiling; built into Input → Pitch → Gain → Output, the header plays the sound
-  //        through it, and a `Play sound` naming it sends the game's voice the same way.
+  //        through it, and a `Play sound` naming it sends the game's voice the same way. The pitch
+  //        comes from a parameter `depth` of the Input: the header has a field for it, and a
+  //        `Sound FX parameters` node hands the game's value in.
   await showTab('scene');
   await clickText('+');
   await pickAssetType(t, 'Sound FX');
@@ -309,8 +311,8 @@ export async function sound(t) {
     fx.name = 'Low';
     fx.graph = ${JSON.stringify({
       nodes: [
-        node('fx-in', 'SoundFxInput', 0, 0),
-        node('fx-pitch', 'SoundFxPitch', 220, 0, { semitones: -12 }),
+        node('fx-in', 'SoundFxInput', 0, 0, {}, [{ key: 'depth', kind: 'number', default: -12 }]),
+        node('fx-pitch', 'SoundFxPitch', 220, 0),
         node('fx-gain', 'SoundFxGain', 440, 0, { gain: -6 }),
         node('fx-out', 'SoundFxOutput', 660, 0),
       ],
@@ -318,12 +320,15 @@ export async function sound(t) {
         edge('fx-e1', 'fx-in', 'out', 'fx-pitch', 'in'),
         edge('fx-e2', 'fx-pitch', 'out', 'fx-gain', 'in'),
         edge('fx-e3', 'fx-gain', 'out', 'fx-out', 'in'),
+        edge('fx-e4', 'fx-in', 'depth', 'fx-pitch', 'semitones'),
       ],
     })};`);
-  const fxBuilt = await json('{ info: __gm.soundfx.info(), preview: __gm.soundfx.preview() }');
+  const fxBuilt = await json(
+    '{ info: __gm.soundfx.info(), preview: __gm.soundfx.preview(), params: __gm.soundfx.params() }',
+  );
   check(
-    'Input → Pitch → Gain → Output compiles to two effects, and Play is offered',
-    fxBuilt.info === '2 effects' && fxBuilt.preview.play === true,
+    'Input → Pitch → Gain → Output compiles to two effects, Play is offered, depth starts at its default',
+    fxBuilt.info === '2 effects' && fxBuilt.preview.play === true && fxBuilt.params.depth === -12,
     JSON.stringify(fxBuilt),
   );
   await evaluate('__gm.sound.stopAll()');
@@ -337,6 +342,16 @@ export async function sound(t) {
     JSON.stringify(heardFx),
   );
   await evaluate('__gm.sound.stopAll()');
+  await evaluate('__gm.soundfx.setParam("depth", 5)');
+  const beforeParam = await stats();
+  await click(fxPlayAt.x, fxPlayAt.y);
+  const heardParam = await waitFor(stats, (s) => s.started > beforeParam.started);
+  check(
+    'the header plays with the value its depth field is set to',
+    heardParam.last?.pitch === 5 && heardParam.last.stages === 1,
+    JSON.stringify(heardParam),
+  );
+  await evaluate('__gm.sound.stopAll()');
   await showTab('scene');
   await mutate(`
     const graph = __gm.state.project.assets.find((a) => a.id === 'sn-logic').graph;
@@ -352,6 +367,25 @@ export async function sound(t) {
   await stop();
   await mutate(`
     const graph = __gm.state.project.assets.find((a) => a.id === 'sn-logic').graph;
+    graph.nodes.push(${JSON.stringify(
+      node('sn-fxp', 'SoundFxParameters', 0, 120, { soundFxAsset: fxId, depth: 7 }, [
+        { key: 'depth', kind: 'number' },
+      ]),
+    )});
+    graph.edges.push(${JSON.stringify(edge('sn-e-fxp', 'sn-fxp', 'params', 'sn-play', 'fxParams'))});`);
+  const beforeGameParam = await stats();
+  await play();
+  const gameParam = await waitFor(stats, (s) => s.started > beforeGameParam.started);
+  check(
+    'a Sound FX parameters node hands depth 7 to the game’s voice',
+    gameParam.last?.pitch === 7 && gameParam.last.stages === 1,
+    JSON.stringify(gameParam),
+  );
+  await stop();
+  await mutate(`
+    const graph = __gm.state.project.assets.find((a) => a.id === 'sn-logic').graph;
+    graph.nodes = graph.nodes.filter((n) => n.id !== 'sn-fxp');
+    graph.edges = graph.edges.filter((e) => e.id !== 'sn-e-fxp');
     Object.assign(graph.nodes.find((n) => n.id === 'sn-play').params, { loop: '', fx: '' });
     const project = __gm.state.project;
     project.assets = project.assets.filter((a) => a.id !== ${JSON.stringify(fxId)});`);