Low Pass filter for a recorded message.

Hello guys! I'm quite new in Matlab Signal processing and I would wonder if anybody can help me with a low pass filter for a recorded WAV file. It must be really simple but i searched on the internet and i found a lot of complicated ways of filtering a signal. So, I must record a message, I must filter it in matlab, calculate its spectrum (with fft i think), and then listen the message again. What differences should I observe and why? it would help me so much if you can comment the lines and if you can show me a parallel example for a high pass filter. Thank you so much!

Answer 1

[Star Strider]

If you have R2018a or later, the easiest way is to use the lowpass (link) function. It designs an efficient elliptical filter. (Note that if you use the second ‘d’ output, use the filtfilt function, not filter as suggested in the lowpass documentation.) Use the ‘Fs’ output of your audioread call to define the sampling frequency for your filter.

If you cannot use the lowpass function, filters are very easy to design in MATLAB using the more basic functions such as ellipord )link), ellip (link), and (since you will be requesting the ‘[z,p,k]’ output), the zp2sos (link) functions.

Remember to evaluate your filters using the freqz function to be certain they are doing what you designed them to do.