I designed a digital FIR filter using the frequency sampling method and I got the filter coefficients.

Now, I'm working on a real-time (time-domain) application (a numerical simulation) where the time step is varying (depending on the case). In this application the motion of a device (let's call it X(t) ) is function of time and has to be filtered with the filter designed. The problem is that the motion of this device has to be defined at each variable time step but the filtering procedure (convolution with filter coefficients) has to be applied ONLY at some specific time steps (related to the frequency sampling of my filter).

Does anyone know how to solve it?

best regards,

Benedetto