NST Audio FIR Filtering

FIR filters have become increasingly popular in pro-audio in recent years, driven by the availability of more powerful DSPs which are able to process multiple FIR filters in real-time. However, whilst FIR filters are a powerful tool they are also frequently misunderstood.

FIR Filters

The alternative to IIR filters is the FIR filter which, as the name suggests, are designed using a fixed length impulse response. Actually, the normal design method for FIR filters is to design the frequency and phase response, then calculate an inverse Fourier transform to generate the impulse response (which is the FIR filter itself). From a design point of view, this has many advantages as it allows the design of filters with complex frequency responses without any of the side-effects of a non-linear phase response to cause problems in the acoustic system.

Both IIR and FIR filtering techniques have applications in pro-audio, but care must be taken when choosing which is best suited for a particular application as both methods have benefits and drawbacks. There is sometimes a perception that FIR filters are superior, mainly because of the control they give over the phase response. While there are many powerful advantages to FIR filters, this functionality comes at a cost, not only in terms of group delay, but also the restriction of the frequency range which can be controlled.