Overview: Is a filter necessary if you know the frequency content of your waveform? The answer is no, you will not need a filter. The problem in the real world is that you are never sure what frequencies are on your signal line. Some of the high frequency noise sources that affect your data include switching power supplies, monitors, RF noise from computers, AC power sources, etc. If you do not use the right filter, it is like playing roulette; you may collect good data and you may collect bad data, you can never tell. The only way to guarantee valid data is to use an anti-aliasing filter.