In dewesoft X SP5:
I need to filter some data with a 2 pole low pass filter formed from two different single pole filter sections.
Seems a simple thing: just feed the output of one single pole IIR filter to the input of another IIR filter.... but it doesn't always work.
Generally adding a second filter to the cascade does work, but once the original filter is altered the output of the second filter becomes a constant 0. Changing the filter back to the original specification doesn't make it work again.
The first filter is a 2 pole 2.4Hz low pass
I add a second filter (a 1 pole 0.5Hz IIR) to filter the output of the first filter .. the output of the second filter is OK
I modify the original filter to a 1 pole 2.4Hz LP IIR filter; now the output of this first filter is OK, but the output of the second filter is 0.
I return the original filter to a 2 pole 2.4Hz filter; the output of the first filter is still OK but the output of the second filter is still 0.
Bug? Fix? Anyone have the answer?
More information .... in fact the above problem is only present in Post Maths.
I created a new setup file on a PC with the dewe-43 plugged into it, and everything works fine.
But when attempting to create a filter cascade in Post Maths (ie reprocessing an old data file) it doesn't.
this is already fixed and it works with DEWESoft X1 SP6.