The observation on the graph of the original signal (in frequency domain magnitude and phase and time domain) shows us the exact wave files sounds signal and its plot in specified domain.
While the observation on the noisy signal shows us a graph with added noise signal into the original sounds. This clearly can be seen in the part of the graph where an unwanted noise signal in the high frequency exist.
From that noise signals plots in frequency domain , we can obtain the cutoff we wanted to make for filtering, and also the passband.
After calculation of all wanted parameters needed is done and inserted into matlab codes( please refer the matlab mfiles page and also the results page for the details of calculation works ).
As the filtered is done and the filtered sounds is listened and the outcome is an almost noise free signal, which sounds as the original.
The only difference found here is the sounds of filtered signal is softer compare to the louder original signal.
From the plotted filtered signal graph(in the frequency magnitude and phase and time domain) , we can clearly see that the magnitude has decreased compared to the original plot but the shape remains the same. That is where the unwanted signal has been removed and the outcome is the original like graph shape.
Filtered sounds for part 1 and part 2 of the experiment are almost the same. No difference is observed here(maybe there exist a very small difference which we couldn't observe).