@thi.ng/dsp/svf.js

Composable signal generators, oscillators, filters, FFT, spectrum, windowing & related DSP utils

import { PI } from "@thi.ng/math/api";
import { clamp05 } from "@thi.ng/math/interval";
import { AProc } from "./aproc.js";
const svfLP = (fc, q) => new SVF("lp", fc, q);
const svfHP = (fc, q) => new SVF("hp", fc, q);
const svfBP = (fc, q) => new SVF("bp", fc, q);
const svfNotch = (fc, q) => new SVF("notch", fc, q);
const svfPeak = (fc, q) => new SVF("peak", fc, q);
const svfAllpass = (fc, q) => new SVF("all", fc, q);
class SVF extends AProc {
  constructor(_type, _freq, _q = 0.5) {
    super(0);
    this._type = _type;
    this._freq = _freq;
    this._q = _q;
    this.reset();
    this.computeCoeffs();
  }
  _a1;
  _a2;
  _c1;
  _c2;
  _g;
  _k;
  reset() {
    this._c1 = this._c2 = this._val = 0;
    return this;
  }
  next(x) {
    const { _c1, _c2 } = this;
    const x1 = this._a1 * _c1 + this._a2 * (x - _c2);
    const x2 = _c2 + this._g * x1;
    this._c1 = 2 * x1 - _c1;
    this._c2 = 2 * x2 - _c2;
    switch (this._type) {
      case "lp":
        return this._val = x2;
      case "hp":
        return this._val = x - this._k * x1 - x2;
      case "bp":
        return this._val = x1;
      case "notch":
        return this._val = x - this._k * x1;
      case "peak":
        return this._val = 2 * x2 - x + this._k * x1;
      case "all":
        return this._val = x - 2 * this._k * x1;
    }
  }
  set(fc, q) {
    this._freq = fc;
    this._q = q;
    this.computeCoeffs();
  }
  setFreq(fc) {
    this._freq = fc;
    this.computeCoeffs();
  }
  setQ(q) {
    this._q = q;
    this.computeCoeffs();
  }
  computeCoeffs() {
    this._freq = clamp05(this._freq);
    const g = this._g = Math.tan(PI * this._freq);
    this._k = 2 - 2 * this._q;
    this._a1 = 1 / (1 + g * (g + this._k));
    this._a2 = g * this._a1;
  }
}
export {
  SVF,
  svfAllpass,
  svfBP,
  svfHP,
  svfLP,
  svfNotch,
  svfPeak
};