PolyBLEPOscillator.ts

import { Oscillator, OscillatorArgs, OscillatorMode } from "./Oscillator";

export class PolyBLEPOscillator extends Oscillator {
  last_output: number = 0;
  constructor(oscillator_args: OscillatorArgs) {
    super(oscillator_args);
    this.update_increment();
  }
  poly_blep(t: number) {
    const dt = this.phase_increment / (2 * Math.PI);
    if (t < dt) {
      t /= dt;
      return t + t - t * t - 1;
    } else if (t > 1 - dt) {
      t = (t - 1) / dt;
      return t + t - t * t - 1;
    } else {
      return 0;
    }
  }
  next_sample(): number {
    let value = 0;
    const t = this.phase / (2 * Math.PI);
    if (this.oscillator_mode == OscillatorMode.OSCILLATOR_MODE_SINE) {
      value = this.naive_wave_form(OscillatorMode.OSCILLATOR_MODE_SINE);
    } else if (this.oscillator_mode == OscillatorMode.OSCILLATOR_MODE_SAW) {
      value = this.naive_wave_form(OscillatorMode.OSCILLATOR_MODE_SAW);
      value -= this.poly_blep(t);
    } else {
      value = this.naive_wave_form(OscillatorMode.OSCILLATOR_MODE_SQUARE);
      value += this.poly_blep(t);
      value -= this.poly_blep((t + 0.5) % 1);
      if (this.oscillator_mode == OscillatorMode.OSCILLATOR_MODE_TRIANGLE) {
        value =
          this.phase_increment * value +
          (1 - this.phase_increment) * this.last_output;
        this.last_output = value;
      } else {
        value =
          this.naive_wave_form(OscillatorMode.OSCILLATOR_MODE_SQUARE) - value;
      }
    }
    this.phase += this.phase_increment;
    while (this.phase >= 2 * Math.PI) {
      this.phase -= 2 * Math.PI;
    }
    return value;
  }
}