quantize note frequency

package.json

@@ -11,6 +11,7 @@
   },
   "dependencies": {
     "@react-hook/resize-observer": "^2.0.2",
+    "@tonaljs/note": "^4.11.0",
     "classnames": "^2.5.1",
     "immer": "^10.1.1",
     "react": "^18.3.1",

src/synth/SoundNodeState.ts

@@ -1,27 +1,26 @@
-import { Node, State, useAppStore } from "../App.store.ts";
+import { Node, useAppStore } from "../App.store.ts";
 import { posToTime } from "./bpm.ts";
 import { mapObjectValues } from "../helpers.ts";
+import { posToFreq } from "./note.ts";
 
 export type SoundNodeState = {
   time: number;
   length: number;
   freq: number;
 };
 
-function computeSoundNodeState(node: Node, state: State): SoundNodeState {
+function computeSoundNodeState(node: Node): SoundNodeState {
   return {
     time: posToTime(node.x),
-    freq: 100 + ((state.size[1] - node.y) / state.size[1]) * 800,
+    freq: posToFreq(node.y + node.height / 2),
     length: posToTime(node.width),
   };
 }
 
 export function getSoundNodeStates() {
   const state = useAppStore.getState();
 
-  return mapObjectValues(state.nodes, (node) =>
-    computeSoundNodeState(node, state),
-  );
+  return mapObjectValues(state.nodes, (node) => computeSoundNodeState(node));
 }
 
 export function subscribeToNodeState(
@@ -30,7 +29,7 @@ export function subscribeToNodeState(
 ) {
   useAppStore.subscribe((state, prevState) => {
     if (state.nodes[id] !== prevState.nodes[id]) {
-      cb(computeSoundNodeState(state.nodes[id], state));
+      cb(computeSoundNodeState(state.nodes[id]));
     }
   });
 }

src/synth/note.ts

@@ -0,0 +1,23 @@
+import * as Note from "@tonaljs/note";
+import { useAppStore } from "../App.store.ts";
+
+const availableNotes = 24;
+const base = 60;
+
+export function posToFreq(pos: number) {
+  const { size } = useAppStore.getState();
+  const height = size[1];
+  const noteMidi =
+    pos === 0
+      ? base - 12
+      : base -
+        1 -
+        12 +
+        Math.ceil(((height - pos) / height) * (availableNotes + 1));
+
+  const freq = Note.freq(Note.fromMidi(noteMidi));
+  if (freq === null) {
+    throw new Error("could not determine note frequency!");
+  }
+  return freq;
+}