How to create a function for filtered data using a Nth order lowpass digital Butterworth filter.

This question gives us the body of the function in general to work with.

function [filtereddata]= filterdata(rawdata, samplingrate, cutoff, filterorder)

the raw data is given as transducer(variable) data, as well as the samplingrate(variable) outside of the function. I am not sure how to identify the cutoff value for a Butterworth filter.

Since I am only using 2 columns of data, I think the filterorder is 1 as the function will be re-written for the other raw data.

My question is: how to identify the cutoff frequency and what the filterorder would be when making the butterworth function?

Answer 1

[Wayne King]

Hi Raymond, the cutoff frequency should be a design parameter for you. You should decide what the cutoff frequency is based on what frequency content you want to pass and what frequency content you want to attenuate. I'm sure the filter order will be greater than 1.

Once you determine your cutoff frequency, you can use buttord() to determine the lowest order for a Butterworth filter design (you'll also need to like about passband ripple and stopband attenuation) that meets your specifications.

[Walter Roberson]

"you'll also need to like about [...]" ? I think a word or three got missed?