Sampling and Filtering Question

I have a device that collects data at 50Hz. I use the device to capture a sine wave that has a frequency of 0.16Hz. When I am building a filter for this data using Matlab (butter function) where the cutoff frequency is Wn and is 0 < Wn < 1 where 1 is half of the sample rate, is it referring to the 50Hz of the device or the 0.16Hz of the sine wave I am capturing?

Answer 1

[Star Strider]

It is referring to the 50 Hz of the device.

The normalising frequency that is half the sampling frequency is known as the Nyquist frequency. So you normalise with respect to 25 Hz.