I have some data that is sampled at a certain rate (16384Hz). I am only interested in the 10-30Hz region, so I want to downsample the data. My idea to do this goes as follows:
- I apply some kind of filter to the data so the PSD quickly drops after about twice the maximum frequency of interest (60Hz). This filter should approach 0 gain after about 10Hz of the cutoff (70Hz).
- I fold the filtered PSD on itself so that it goes up to 60Hz. The residual power from the 60-70Hz region will fall in the 0-10Hz region when folded, and, since I don't care about these frequencies, it won't affect the analysis.
- I have now resampled the data and can transform it back to the time domain as needed.
So far, I have tried to filter the PSD using a Butterworth filter, but I can't figure out how to make it drop to ~0 fast enough (from ~1 at 60Hz to ~0 at 70Hz). I have the following questions about this procedure:
- Does it make sense? Is this a good way to downsample the data given the constraints that I have given?
- Is it correct that I should keep the frequencies up to at least twice the maximum frequency of interest (60Hz)? In order to keep the data Nyquist sampled.
- Is a Butterworth filter the way to go? Or should I use some other kind of filter?
Excuse me if this question is not well formulated, or if I'm not making any sense, I am very new to the subject and still trying to figure out what exactly it is I'm doing. Thanks in advance!