After doing both the FIR and IIR  filter design, we can see that signal in frequency domain give us a better interpretation on the properties of the signal. 
        Distortion noise is basically a higher frequency signal that combine with the original signal. Therefore get rid of the noise, we can simply use filter function to filter up the signal above 2000 hz for instance . 
         But these filter design has one weak point. In case the original signal and the distortion noise are all within the same frequency and, filter function is unable to do so.