Question on designing a filter to remove noise from a audio signal

Here is the question ask from my assignment:

I do not understand how I would go at designing the filter to take care of this problem. So could you please help me figure out what I would need to do at least with the process I would go at doing this from the filter type to choose and how to solve for the specifications needed for it. Any advice or help would be appreciated thank you!

I will post the two .mat files on this question as well if you would like to see them

Answer 1

[Daniel kiracofe]

step 1: analyze the signal and see if you can determine what frequencies are to be kept and what frequencies are to be discarded. FFTs as well as possibly short-time fourier transforms will be helpful here. You will also need some a priori knowledge of the problem domain (i.e. what frequencies are typically contained in human speech). Your instructor has been kind enough to give you versions with and without the noise, so comparison between the two should show you the frequency cutoff.

step 2: design a filter. start with a first order butterworth lowpass filter, with a cutoff frequency that is between the frequency you think should be kept and the frequency you think should be discarded.

step 3: analyze the filtered signal the same way you analyzed the original signal to see what changed. Also play it back to hear the difference.

step 4: try some other types of filters to see if you can get something better than a 1st order butterworth. e.g. try higher orders, different cutoff frequencies, and different filter types.

Some of the tutorials on my webpage may be helpful to you: http://mechanicalvibration.com/tutorial.html