Dan <chunhoishere@yahoo.com.hk> wrote in message <11748494.1236096638508.JavaMail.jakarta@nitrogen.mathforum.org>...
> Actually, i have tried several ways to measure the frequency response, like using the built in "tfestimate" finction in matlab. However, i am not sure the result is correct or not. The plot in in normalized frequency, any hint for me to change it to frequency???
>
> So, do you mean:
>
> H = Pyy/Pxx << this is not the real frequency response?? what do you mean by amplitude characteristics(real module)??
>
> Can you suggest me some ways to do the cross power spectral density on the input x and output y??
> I have tried : "cpsd(x,y)" in matlab, however, it seems that it is not correct
>
> Thanks,
> Dan
Hello Dan,
My answer is not complete. The reason is simple, I do not have Signal processing toolbox functions of which you tried to apply functions (tfestimate, cpsd). However, you say that there is an error in cpsd. Did you try to copy the example from the documentation and run it?
I looked on the Mathworks home page , selected Support,Browse by Product,
Signal Processing Toolbox and then in Option 2: Documentation. In Contents select Statistical Signal Processing and in it Spectral analysis. You will get good survey of it.
If you open Function Reference the in a group of functions Statistical signal processing the function cpsd is described. There is an example that you can run. If the resuilt of the run are thesame as those in documentation, you have to look for errors in your application. The similar holds for the function fpestimate. Test the example.
If the example tests don't give the same results, You would have to set up the function of welch PSD estimate you yourselves. The formulae are in the above documentation.
It is all what I can tell you now.
Best regards.
Mira
