Short for Finite Impulse Response Filter, an FIR is a type of digital process that looks back in time to a fixed number of previous samples in order to generate a result. Example: Outbound sample is equal to an average of the last 4 inbound samples. Because of the nature of FIR filters and the fact that they are only of finite length, they can be made in such a way as to not cause any phase non-linearity with the signal. For this reason they are often used in areas where filtering needs to be done without consequences to the signal in regards to phase, such as in anti-aliasing filters and reconstruction filters in A/D and D/A converters as well as sample rate converters. On occasion FIR filters will also be used in simple low pass or high pass filters in digital EQ‘s.