Bode plot for an Array type input signal

Hello, I have two signals (sigA, sigB) stored in two different array variables of type 1000rows x 1column. These two signals are recorded from original hardware that I'm working with.

sigA[] is original input signal (also input to LowPassFilter) sigB[] is the output of LowPassFilter with Cutoff freq. of 10Hz and sampling frequency of 100Hz.

Now, I'd like to verify sigB[] whether sigA is being properly filtered through LPF or not.

Is there anyway, that I can do the bode plot using these two signal and check the Amplitude and Phase response.

If I'm able to do that, then I can generate sigA[] and sigB[] purely in matlab and do the bode plot again. So, I can compare my LowPassFilter in the hardware with that of in matlab.

Thank You

Answer 1

[Rajiv Singh]

Looks like you need to generate the power spectrum of the input signal and compare that to the spectrum of the output. Look in Signal Processing Toolbox (help "spectrum") for various ways of computing signal spectra.

BODE plot is really for looking at the frequency response of a system (the low pass filter in your case). Since you do not know this system, you will need to "estimate" it using the input/output signals that you have recorded. This you can do by using identification routines in System Identification Toolbox (see tfest in R2012a for example, or procest/pem/n4sid in older releases). Then you can use the "bode" command to view the mag/phase of the frequency response of the estimated model.

For model-free (non-parametric) generation of frequency response from I/O signals you can also check out tfestimate (Signal Processing Toolbox), spa/spafdr/etfe (System Identification Toolbox).