LowPass filter order in Signal processing

Hi everyone,

I'm using signal analyzer app to filter data acquired by a load cell, the time values is in seconds. I want to filter data using a LowPass filter, but how can I know the order of this filter? I don't see the possibility to choose this option in the app.

I read that " lowpass uses a minimum-order filter with a stopband attenuation of 60 dB and compensates for the delay introduced by the filter", but that means I'm using a first oreder filter?

Thanks

Answer 1

[Star Strider]

The signalAnalyzer App is likely not going to be able to do what you want, since it analyzes the signal without designing any filters.

I suggest using the designfilt function instead to actually design the filter, once you decide what you want to do.

However it is relatively trivial to write your own Fourier transform code and then use the more recent (R2018a and later) filter design functions to design your filters. See for example my Answer to Removing jumps from data when plotting a graph doing exactly that sort of analysis and filter design. That code analyses the signal in the frequency domain, and then designs and implements an appropriate filter using Command Line filter design and implementation functions.

Answer 2

[Frantz Bouchereau]

Minimum order does not mean unit order. Minimum order is the smallest order for which the filter can achieve 60 dB attenuation (or the specified attenuation). Signal Analyzer designs a minimum order lowpass filter using the designfilt function and then filters the data with that filter.

If you want to filter a signal with a specific filter with a pre-defined order you can add a custom function to the app that filters the data using your filter. See this documentation page to learn how to add custom functions to the Signal Analyzer app:

https://www.mathworks.com/help/signal/ug/preprocess-signals.html