No-delay filter

[NI-DAQueen]

I am looking for a filter that will NOT introduce a delay into my system.  In other words, I do not want there to be a delay between the filtered signal and the unfiltered signal.

Does such a filter exist in LabView?

Presently, I am using a Butterworth filter which does a great job of filtering, but which introduces a delay into my system. 

[johnsold]

All filters have delay.

You can use an all pass filter (or delay equalizer) to delay the unfiltered signal by an equal amount so that both signals are synchronized.

Be aware also that filters may have different delay at different frequencies, so the delay matching may not be trivial.

Lynn

[Kevin_Price]

Adding to Lynn's comments:

You may want to consider a Bessel filter -- it can give you near-constant "group delay".   I used this characteristic in an app where lowpass filtering was necessary, but where correlation in the time domain was also important.   It lessens the potential problem of delaying low frequency content and medium frequency content by different amounts, thus shifting the relative locations of peaks and troughs.  All freq content is shifted similarly, so peaks and troughs remain relatively correlated.

-Kevin P.