[matplotlib-devel] Fwd: possible issue with _spectral_helper function in matplotlib/mlab.py when compensate windowing loss

[Thomas C. <tca...@gm...>]

Forwarding an email to the devel list, we seem to have an error in mlab.

Dimitris:  Please send future issues like this directly to the mailing list
or create an issue on GH.

---------- Forwarded message ---------
From: Dimitris Daniel <dda...@gm...>
Date: Thu, Mar 26, 2015 at 4:04 AM
Subject: possible issue with _spectral_helper function in
matplotlib/mlab.py when compensate windowing loss
To: <tca...@gm...>, <mar...@gm...>


Dear Mr. Thomas and Mr. Martin,

First of all I would like to thank you for your work.
My name is Dimitris Daniel and I use _spectral_helper in a process.

I think that there is a problem when we try to compensate windowing loss.

You use the row:
result /= (np.abs(windowVals)**2).sum()

However as I can see in Bendat & Piersol Sec 11.5.2. (see attached 3.png) I
think the right is something like:

result *= np.sqrt((np.ones(NFFT)**2).sum() / (np.abs(windowVals)**2).sum())

Actually I had some correlation problems with the data from a customer of
my for which I build a script for Signal Analysis.

He gave me the input signal and the output he gets from the hardware he is
using.

I use some parts from your functions and it was not possible to get the
same results.
By changing this row the results are matching together.


Am I missing something or am I right.

Thank you very much for your time and sorry for any inconvenience.

I am looking forward to your response.
Best Regards,
Dimitris Daniel