Is it possible to use Zero phase filter for continuous filtering?

Question

I have to filter a large amount of data without any phase shift from original signal. The Zero phase filter does it but it has to be used in single shot mode. It doesn't have any "Init/Cont" input terminal which other filters have. Is there any way to implement zero phase filtering to filter data continuously?

Answer 1

AJ_CS wrote:
The zero phase filtering method seen in your thread will work, if the filtering happens as a single shot operation. It will remove the edge effects of zero phase filtering.
But for an application wherein data arrives as small blocks, it has to filter each block of the data and also it has to maintain the continuity of filtering. 
For example in every 1 sec, I'm getting 500 samples of data. I have to use this zero phase filtering for each block of 500 samples, in each second. But what seems to happen is, between the end of one data block and beginning of next data block( between 500th sample and 501th sample or between the end of 1st sec data and beginning of 2nd sec data), there is a discontinuity, or distortion.
Normal IIR (butterworth)filter maintains this continuity between data blocks, but with phase shift.
Zero phase filtering doesn't introduce any phase shift but it is unable to maintain the continuity, it seems. 
Is it possible to have a filter meeting both these requirements?
In a nut-shell yes.
It will require you apply the technique I illustrated in that thread repeatedly each time you get an update. The "reflection about the end points" cleans up the disconinuities. I suspect there may be some theory that what you end up with can not be proven using any formal math approach, but it closely mimics what the human mind does when we ask ourselves "If it continues like that that, what do I expect?".
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