setType(t) {
    this.biquad.type = t;
    this._untoggledType = this.biquad.type;
  }
Set the type of a p5.Filter. Possible types include:
 "lowpass" (default), "highpass", "bandpass",
 "lowshelf", "highshelf", "peaking", "notch",
 "allpass".

 @method  setType
 @param {String} t