Explain in detail about the operation of zerophasefilter.vi

[sayaf]

Description needed in detail.
Thanks.

[Johnner]

Sayaf,

The community needs more information from you before it can help:

- Where did you get this VI? (Is it from NI or from some external vendor?)
- Did it come with any documentation?
- What aspect of the operation are you asking about: theory, algorithm, usage, etc?

Be more descriptive, and you'll probably get some help.

Regards,
John

[sayaf]

Thanks John,
I wanted to know the Theory as well as the Algorithm on which it works. I don't have any documents of it.
Help me out.
sayaf

[Johnner]

Sayaf,

If there is no documentation, it sounds as if this might be a custom VI that one of your colleagues or someone else in the LabVIEW community wrote. It may be that you are using a VI that nobody on this discussion forum has ever seen. Maybe you should attach the VI in a response so that others can take a look.

Perhaps you're generally interested in filtering and the effects that various approaches have on the phase of the signal being filtered?

Either way, you'll probably need to provide a lot more detail (and the VI, ideally), before anyone will really be able to help.

Regards,
John

[NeilR]

Hi Sayaf

There is a reference to the zerophasefilter.vi here which includes a description and a further reference to a publication.
There is also an example to download.
Hope this is of some help.

[Ben]

I palyed with this some years ago.

It runs off the idea that if you run a signal through a filter
a) Only specific freq components of the signal will be passed.
b) A phase shift that is on the order of the filter is introduced.

When running the same signal through the same filter again,
a) The freq components that passed before are still passed but the componenets that were removed in the first passed are not present so they are not remove.
b) Another phase shift is introduced.

The zero pahse shift filter runs the signal through the filter (you pick your favorite flavor) and then the signal is reflected about the Y-axis effectively reversing time. THe revers signal is run through the filter a second time but now the phase shift is is in the oposite time direction. This effectively cancels out the original phase shift.

These are handy if you want to correlate a filtered event with an un-filtered event.

BUT

You do not get something for nothing (2nd Law of Theromdynamics).

In getting better phase information you loose signal info at the front end and back end of the waveform.

I hope this helps,

Ben

[sayaf]

Thanks Ben,
But I need the explaination about what actual procedure/steps carried out in zerophasefilter.vi or recommend some document online regarding Forward/Backward filtering phenomenon with an example.

Thanks once again
sayaf.

[Ben]

NeilR provided a link to that information already.

He suggested this URL

http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3DCF756A4E034080020E74861&p_node=DZ52015&p_submitted=N&p_rank=&p_answer=&p_source=External

Have you looked at that?

Ben