Filters >> FIR vs. IIR Digital Filters and Recursive vs. Non-Recursive Filters Key Features The higher the order of a filter, the sharper the stopband transition The sharpness of FIR and IIR filters is very different for the same order A FIR filter has an equal time delay at all frequencies, while the IIR filter's time delay varies with frequency. Usually, the biggest time delay in the IIR filter is at the filter's cutoff frequency. The term 'IR' (impulse response) is in both FIR and IIR. The term 'impulse response' refers to the appearance of the filter in the time domain. 1. What Is the Difference Between an FIR and an IIR Filters? The two major classifications of digital filters used for signal filtration are FIR and IIR....