Re: discuss [bug #43305] Hamming etc. windows are wrong

[Doug Stewart]

On Fri, Jan 2, 2015 at 7:38 PM, Jerry <address@hidden> wrote:

On Dec 30, 2014, at 10:48 AM, Doug Stewart <address@hidden> wrote:

Rik asked me to start a discussion here about how to fix this bug.

 The real question is:   Should we do as Matlab did or should we make the default  

 be the more mathematically correct method.

 I am arguing for the mathematically correct method as the default.

 ( I will be happy even if I loose  the argument)

I will post my argument in the next chapter :-)

Comment are welcome.

I just moments ago wrote a response to Doug Stewart's note in a related thread, "Ltfat tria window", in which he gets a window (triangle in his case) which is rotated from what might be expected. That is, the triangle window is high at the ends and low in the middle. Of course this is convenient if one wants to apply it to a normally-indexed DFT result (0 .. N - 1) whereby the high frequencies are attenuated more than the low frequencies. As I note there, both types of windows are applicable, typically unrotated windows for applying to time series and rotated windows for applying to (unrotated) frequency series.

So while we are attending to fixing up Octave's window functions I think we should add another option to return a rotated version.

I suppose it's obvious but by rotated I mean circularly shifted by N / 2 or N / 2 - 1 depending on the direction of the shift.

Jerry

P.S. Here's a clarification on my name(s). Sorry for any confusion.

I am the OP on the Hamming etc. window bug; my login name is Oscar Ruitt which is an alias. (It's a joke in English if you say it quickly.) My list e-mail address usually includes lanceboyle which is another joke. My real name is Jerry Bauck and I normally just sign as Jerry so as to avoid polluting my internet namespace.

-- 

   Things are gradually getting clearer in my mind as to the confusion between  different systems.

1) LTFAT windows are rotated from pkg signal windows.

2) The triang window from signal pkg is a modified triangle window from the Harris documentation.

3) The bartlett window from signal pkg is a triangle window from the Harris documentation.

I am used to the Harris document from 1978. I taught from it for many years, so when we started talking about FFTs and widows my mined just goes to this document, which I got in 1982!!!!

Attaches is a simple overview of the problem.

I am now going to look in depth at the FFT of each window and see if there is any really compelling reason to use one version as the default.

Also I agree that we should include option 3 -- "rotated".

Stay tuned!

Doug

P.S.  thanks for clarifying your name Jerry.

windows_for_Octave_ch2.pdf
Description: Adobe PDF document