I am using the function fdesignlowpass in Matlab on a signal

I am using the function fdesign.lowpass in Matlab, on a signal that is sampled at 8kHz. I am making a filter for a speech signal and want to filter out gaussian noise, i have found the fundamental freq. to be around 343Hz with FFT.

So I am using the command in Matlab:

Should my sample rate be 8000/2?

Solution

Ans)

It is better to keep the sampling frequency of both the signal and filter same which makes whole system working under same sampling frequency for the given input analog signal ,so your choice is 8kHz i.e 8000 Hz,