Extract a Bode Plot from a filter

I have this low pass filter and need to extract the bode plot of it.

[b,a]=butter(3,50/1000,'low');

freqz function isn't working, possibly because it's not a digital filter. Could someone guide me on how I can do it.

[Geoff Hayes]

Karl - please clarify what you mean by freqz function isn't working. Are there errors or something else?

[Karl Rueth]

Yes it was, Freqs has to be used for analogue filters .. Thanks to Star Rider

Answer 1

[Star Strider]

Use the Signal Processing Toolbox freqs (link) function for continuous filters, or freqz (linked to at the end of that documentation) for discrete filters. You can also get the amplitude and frequency outputs.

[b,a]=butter(3,50/1000,'low');

figure
freqs(b, a)

[Karl Rueth]

Thanks .. It worked

[Star Strider]

As always, my pleasure.