toggle() {
    this._on = !this._on;

    if (this._on === true) {
      this.biquad.type = this._untoggledType;
    } else if (this._on === false) {
      this.biquad.type = 'allpass';
    }

    return this._on;
  }
Toggle function. Switches between the specified type and allpass

@method toggle
@return {boolean} [Toggle value]