State Variable Filter initial implementation

CHANGELOG.md

@@ -1,3 +1,10 @@
-# Synthlet
+# synthlet
 
 ## 0.1.0
+
+Initial implementation of:
+
+- ADSR
+- White Noise
+- State Variable Filter
+- Wavetable Oscillator

LICENSE.md

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2023 Daniel Gómez
+Copyright (c) 2023-2024 Daniel Gómez Blasco (danigb)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -44,6 +44,7 @@ npm i @synthlet/adsr
 
 ## Documentation
 
-- [ADSR](/packages/adsr/README.md)
-- [Noise](/packages/noise/README.md)
-- [WavetableOscillator](/packages/wavetable-oscilllator/README.md)
+- [ADSR](/packages/adsr)
+- [Noise](/packages/noise)
+- [StateVariableFilter](/packages/state-variable-filter)
+- [WavetableOscillator](/packages/wavetable-oscilllator)

packages/state-variable-filter/CHANGELOG.md

@@ -0,0 +1,5 @@
+# @synthlet/state-variable-filter
+
+## 0.1.0
+
+- Initial implementation

packages/state-variable-filter/README.md

@@ -0,0 +1,14 @@
+# @synthlet/state-variable-filter
+
+> State Variable Filter module for [synthlet](https://github.com/danigb/synthlet)
+
+## Usage
+
+If you're using synthlet, this filter is included by default and exposed by `patch.filter`:
+
+```ts
+import { Patch } from "synthlet";
+
+const patch = new Patch();
+await patch.create([patch.osc(), patch.filter({ type: "lowpass" })]);
+```

packages/state-variable-filter/package.json

@@ -0,0 +1,35 @@
+{
+  "name": "@synthlet/state-variable-filter",
+  "version": "0.1.0",
+  "description": "State Variable Filter module for synthlet",
+  "keywords": [
+    "modular",
+    "synthesizer",
+    "filter",
+    "synthlet"
+  ],
+  "main": "dist/index.js",
+  "module": "dist/index.mjs",
+  "types": "dist/index.d.ts",
+  "files": [
+    "dist"
+  ],
+  "author": "[email protected]",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "devDependencies": {
+    "@types/jest": "^29.5.11",
+    "jest": "^29.7.0",
+    "ts-jest": "^29.1.1"
+  },
+  "jest": {
+    "preset": "ts-jest"
+  },
+  "scripts": {
+    "worklet": "esbuild src/worklet.ts --bundle --minify | sed -e 's/^/export const PROCESSOR = \\`/' -e 's/$/\\`;/'  > src/processor.ts",
+    "lib": "tsup src/index.ts --sourcemap --dts --format esm,cjs",
+    "build": "npm run worklet && npm run lib"
+  }
+}

packages/state-variable-filter/src/__snapshots__/filter.test.ts.snap

@@ -0,0 +1,76 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`SVFilter filters the signal 1`] = `
+Float32Array [
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+  -1,
+  1,
+]
+`;
+
+exports[`SVFilter filters the signal 2`] = `
+Float32Array [
+  -7.058988571166992,
+  -96.1963882446289,
+  -933.3245239257812,
+  -7950.83740234375,
+  -63193.6796875,
+  -481030.5,
+  -3555095.5,
+  -25716442,
+  -183016032,
+  -1285889280,
+  -8941918208,
+  -61654106112,
+  -422081658880,
+  -2872091344896,
+  -19441708433408,
+  -131008733118464,
+  -879299460595712,
+  -5880895244337152,
+  -39209108632502270,
+  -260680291251650560,
+]
+`;
+
+exports[`SVFilter filters the signal 3`] = `
+Float32Array [
+  -1728730658831859700,
+  -11437933590730506000,
+  -75519349223376030000,
+  -497665280641740050000,
+  -3.2738075880989456e+21,
+  -2.150135330517005e+22,
+  -1.4100311966854957e+23,
+  -9.233990443912205e+23,
+  -6.03935217634656e+24,
+  -3.9452060773814655e+25,
+  -2.574315262255496e+26,
+  -1.6780219466165328e+27,
+  -1.0927115680685831e+28,
+  -7.109042947525591e+28,
+  -4.621019964675439e+29,
+  -3.001284075478557e+30,
+  -1.9477740115635436e+31,
+  -1.263136567931854e+32,
+  -8.18576013175832e+32,
+  -5.3012721012231e+33,
+]
+`;

packages/state-variable-filter/src/__snapshots__/worklet.test.ts.snap

@@ -0,0 +1,20 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ProcessorNode has parameter descriptors 1`] = `
+[
+  {
+    "automationRate": "k-rate",
+    "defaultValue": 1000,
+    "maxValue": 20000,
+    "minValue": 16,
+    "name": "frequency",
+  },
+  {
+    "automationRate": "k-rate",
+    "defaultValue": 0.5,
+    "maxValue": 40,
+    "minValue": 0,
+    "name": "resonance",
+  },
+]
+`;

packages/state-variable-filter/src/filter.test.ts

@@ -0,0 +1,23 @@
+import { SVFilter, SVFilterType } from "./filter";
+
+describe("SVFilter", () => {
+  it("filters the signal", () => {
+    const filter = SVFilter(20, SVFilterType.LowPass);
+    const input = new Float32Array(20);
+    for (let i = 0; i < input.length; i++) {
+      input[i] = i % 2 ? 1 : -1;
+    }
+    expect(input).toMatchSnapshot();
+    const output = new Float32Array(20);
+    filter.fill(input, output, {
+      frequency: [10],
+      resonance: [0.5],
+    });
+    expect(output).toMatchSnapshot();
+    filter.fill(input, output, {
+      frequency: [5],
+      resonance: [0.5],
+    });
+    expect(output).toMatchSnapshot();
+  });
+});

packages/state-variable-filter/src/filter.ts

@@ -0,0 +1,83 @@
+/**
+ * Limit the value between min and max
+ * @param value
+ * @param min
+ * @param max
+ * @returns
+ */
+export function clamp(value: number, min: number, max: number): number {
+  return Math.max(min, Math.min(max, value));
+}
+
+export enum SVFilterType {
+  LowPass = 1,
+  BandPass = 2,
+  HighPass = 3,
+}
+
+export type Inputs = {
+  frequency: number[];
+  resonance: number[];
+};
+
+/**
+ * A State Variable Filter following the Andy Simper's implementation described in http://www.cytomic.com/files/dsp/SvfLinearTrapOptimised2.pdf
+ *
+ * Various implementations:
+ * https://github.com/Ardour/ardour/blob/71e049202c017c0a546f39b455bdc9e4be182f06/libs/plugins/a-eq.lv2/a-eq.c
+ * https://github.com/SoundStacks/cmajor/blob/main/standard_library/std_library_filters.cmajor#L157
+ */
+export function SVFilter(sampleRate: number, type = SVFilterType.LowPass) {
+  // Params
+  let $frequency = 1000;
+  let $resonance = 0.5;
+
+  const period = 0.5 / sampleRate;
+  const pi2 = 2 * Math.PI;
+  const freqCoef = 2.0 * sampleRate * period;
+
+  let d = 0;
+  let a = 0;
+  let g1 = 0;
+  let z0 = 0;
+  let z1 = 0;
+  let high = 0;
+  let band = 0;
+  let low = 0;
+
+  function read(inputs: Inputs) {
+    if (
+      inputs.frequency[0] !== $frequency ||
+      inputs.resonance[0] !== $resonance
+    ) {
+      $frequency = inputs.frequency[0];
+      $resonance = inputs.resonance[0];
+      const cutoffFreq = clamp($frequency, 16, sampleRate / 2);
+      const Q = clamp($resonance, 0.025, 40);
+      const invQ = 1.0 / Q;
+      // TODO: review - something weird here (sampleRate * period = 0.5)
+      a = 2.0 * sampleRate * Math.tan(pi2 * period * cutoffFreq) * period;
+      d = 1.0 / (1.0 + invQ * a + a * a);
+      g1 = a + invQ;
+    }
+  }
+
+  function fill(input: Float32Array, output: Float32Array, inputs: Inputs) {
+    read(inputs);
+    for (let i = 0; i < input.length; i++) {
+      const x = input[i];
+      high = (x - g1 * z0 - z1) * d;
+      band = a * high + z0;
+      low = a * band + z1;
+      z0 = a * high + band;
+      z1 = a * band + low;
+      output[i] =
+        type === SVFilterType.LowPass
+          ? low
+          : type === SVFilterType.HighPass
+          ? high
+          : band;
+    }
+  }
+  return { fill };
+}