Re: Ltfat tria window

[Jerry]

On Jan 2, 2015, at 1:59 PM, Doug Stewart <address@hidden> wrote:

On Fri, Jan 2, 2015 at 3:54 PM, Jerry <address@hidden> wrote:

On Jan 2, 2015, at 12:29 PM, Doug Stewart <address@hidden> wrote:

> firwin('tria',11,'1')
> ans =
>
>    0.180328
>    0.147541
>    0.114754
>    0.081967
>    0.049180
>    0.016393
>    0.016393
>    0.049180
>    0.081967
>    0.114754
>    0.147541
>
> --
>
>
> This seems to me to be a mistake.
> T was hoping for a triangle window.

It's rotated.
Jerry

Are all the windows in ltfat rotated?

And by being rotated then the unsymmetrical part is at the high part not the zero location at the end?????

So these windows are used quit differently than the ones in signal pkg.

???

Doug

I don't know. I had to Google ltfat to find out what it is. I suppose the argument for using a rotated window is to attenuate high frequencies more than low frequencies (in the case of most windows such as triangular) and use unrotated DFT results as are normally indexed, that is, 0 .. N - 1.. Long ago (before Octave) I wrote a number of my own windows and included both types—windows that are high in the middle and rotated ones that are high at the ends; I called the rotated ones "frequency" windows exactly for this application.

The window example you give, in addition to being rotated, obviously exhibits the error that I brought up with respect to "[bug #43305] Hamming etc. windows are wrong", as you know as I see that you have participated in that discussion. Maybe you need to take up this issue with the authors of ltfat.

I have sensed in the discussion of the referenced bug that there is claimed a legitimate use of the incorrect windows in spectral analysis. I suspect (but don't know for certain) that this is just another use of the incorrect windows and is "justified" by tradition = years of misuse; I anticipated this (some spurious argument) in my original bug report but I will have to see a really, really good explanation of why the use of incorrect windows is correct in spectral analysis.

BTW, I am the OP on that 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.

Jerry