Cutoff frequency set directly

[LitterWindwind]

Hello, s/f as normalized frequency. When I set the sampling frequency to 250HZ according to the example, and set f to 3hz, I cannot get the ideal result using a simple sine wave test. I would like to ask how to conveniently set the cutoff frequency?

thanks

[adis300]

Are you using a high pass or low pass filter? What does the sine wave look like. You can post code sample here.