Zaxcom ZFR400 Audio Menu17AUDIO MENUHigh Pass FilterThe high pass filter is turned on and adjusted from this menu.The high pass filter range is 70Hz to 220Hz in 10Hz increments.2K Notch FilterThe 2K notch filter is useful in removing digital RF interference that can be introduced into some microphones.HIGH PASS FILTER:90Hz____2K NOTCH FILTERON