Hello,
I've just noticed a problem with the digital filter feature that hasn't occurred to me before. As a test I ran the following script on some accelerometer data:
All it does it repeatedly filter the data so I can look at how it progresses. I was surprised to see how much content there was above the 3 Hz limit. The red trace is the original data, the green is the first filter pass, then blue, orange and purple.
Is this due to the filter degree being only two, so that the roll off is too gentle?
If so, and assuming I use 'force zero phase' and 'correct start/end offset' (and as it happens I'm treating all the channels the same), is there any reason why I can't just wind the filter order right up to give a steeper roll off?
Is the repeated filtering (approximately) the same as increasing the filter order?
An additional point of confusion is the reduction in amplitude below the 3 Hz limit, as seen in an FFT of each filtered signal:
Any advice on a better approach?
Thanks, Simon.