delay filters

[luz2]

How can I compensate the delay introduced by a filter?. Can you help me?

 Thank you very much.

Luz

[TiTou]

Hi Luz,

You question is quite hard to answer since you don't really discribe your problem... Could you for instance post your code (if you have any) and describe your problem/application a little bit more ?
If you need informations about filters, I suggest you have a look at LabVIEW example ("Help" >> "find examples...")

[luz2]

Hello, I send you my problem in images. I'm filtering a signal, and as you can see I have a dalay because of the filter. I would take the signal since the dalay ends, but I would lose the end of the signal, what can I do?

Thanks, Tottou.

Luz

[johnsold]

Luz,

All filters have delays. In general the delay increases as the bandwidth of the filter decreases. Also the delay may vary with frequency. Delay compensation techniques exist: Look at all pass filters. As TiTou said, we need much more information about what you are doing to assist meaningfully.

Lynn

[luz2]

I send you my .vi file, if you can help me it would be nice. I have a delay, but I loose the end of the signal, what can I do?

Thanks

Luz

[luz2]

I send you my .vi file, if you can help me it would be nice. I have a delay, but I loose the end of the signal, what can I do?

Thanks

Luz

[johnsold]

Luz,

I added a note to your VI and changed the filter sample rate as I recommended in another thread. The note is also repeated below.

To make it possible for Forum members without your DAQ hardware and signal sources to help do the following:
1. Run your system and get some typical data.
2. With the data shown on SE-AL, Make Current Values Default.
3. Remove all the DAQmx VIs, remove the Index Array function, and convert SE-AL to a Control.
4. Save and post the modified VI.

Lynn

[Kevin_Price]

I can describe one technique I've seen and used, but I'm not really expert enough on filtering to try to give you pros and cons.  The behavior was fine for my particular app but I've a hunch that the phase effects of this technique might not be desirable across the whole freq band.  At the moment I'm not near my LV PC to check for sure. 

Anyhow, the idea is to filter once forward and then once backward.  The backward filter introduces a "negative delay" that cancels out the original positive delay.  Details: take array A, filter it once to produce array B.  Then reverse array B, filter it exactly the same way to produce array C.   Finally, reverse array C.  The result is doubly-filtered with no delay.

Hopefully others can comment more intelligently about the downsides of this method.  I figure there must be some since you generally don't get something for nothing.  Or as stated by a prof from Engineering school, "The fundamental Law of Engineering is the Conservation of Misery."

-Kevin P.