@thi.ng/dsp/allpass.js

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

import { PI, QUARTER_PI } from "@thi.ng/math/api";
import { clamp05 } from "@thi.ng/math/interval";
import { AProc } from "./aproc.js";
const allpass = (freq) => new AllPass1(freq);
class AllPass1 extends AProc {
  _freq;
  _coeff;
  _z1;
  constructor(freq) {
    super(0);
    this.setFreq(freq);
    this.reset();
  }
  reset() {
    this._z1 = 0;
    return this;
  }
  next(x) {
    const { _coeff, _z1 } = this;
    x -= _z1 * _coeff;
    this._z1 = x;
    return x * _coeff + _z1;
  }
  low(x) {
    return (x + this.next(x)) * 0.5;
  }
  high(x) {
    return (x - this.next(x)) * 0.5;
  }
  freq() {
    return this._freq;
  }
  setFreq(freq) {
    this._freq = clamp05(freq);
    this._coeff = Math.tan(freq * PI - QUARTER_PI);
  }
}
export {
  AllPass1,
  allpass
};