Returns NaN when filtering.

[JoziGila]

I have setup a filter with the parameters (4, 30, 140, 200) for heartbeat filtering from camera brightness variation. However the returned value is NaN for each of the numbers I feed into it.
Butterworth butter = new Butterworth(); butter.bandPass(2, 29, 140, 200); for (Double val: brightness){ processed.add(butter.filter(val)); }

[berndporr]

You have a sampling rate of 29Hz, a centre frequency of 140Hz and a bandwidth of 200Hz?
Check out:
https://github.com/berndporr/iirj/blob/master/src/test/java/uk/me/berndporr/iirj/DetectorTest.java#L52
for an example config:
butterworth.bandPass(2,250,20,15);
...and of course the README and documentation which explain the parameters.

[JoziGila]

I actually don't really know much about DSP and just wanted to find an implementation of butterworth because it was mentioned in a paper that it's used to filter unwanted frequencies such as finger movement from the signal. So even though I have read the doc I don't understand the parameters. My intuition was wrong I guess, I though that sampling rate is the rate of sampling of the signal (29-30fps from the camera), and since the frequencies I want are between 40-230 Source, I interpreted the remaining parameters as 140 (mean of 240 and 40) and the width (+100, -100). Anyways thank you for the quick response, I'll read a bit more about signal processing.