@thi.ng/dsp/onepole.js

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

import { TAU } from "@thi.ng/math/api";
import { clamp05 } from "@thi.ng/math/interval";
import { AProc } from "./aproc.js";
const onepoleLP = (fc) => new OnePole("lp", fc);
const onepoleHP = (fc) => new OnePole("hp", fc);
class OnePole extends AProc {
  constructor(_type, _freq) {
    super(0);
    this._type = _type;
    this._freq = _freq;
    this.setFreq(_freq);
  }
  _a0;
  _b1;
  clear() {
    this._val = 0;
  }
  reset() {
    this.clear();
    return this;
  }
  next(x) {
    return this._val = x * this._a0 + this._val * this._b1;
  }
  setFreq(fc) {
    this._freq = fc = clamp05(fc);
    if (this._type === "lp") {
      this._b1 = Math.exp(-TAU * fc);
      this._a0 = 1 - this._b1;
    } else {
      this._b1 = -Math.exp(-TAU * (0.5 - fc));
      this._a0 = 1 + this._b1;
    }
  }
  filterCoeffs() {
    return {
      zeroes: [this._a0],
      poles: [1, this._type === "lp" ? this._b1 : -this._b1]
    };
  }
}
export {
  OnePole,
  onepoleHP,
  onepoleLP
};