This presentation will show you how to design and implement FIR filters with interesting variations of its spectrum. One example is a remez design with constant level in-band ripple but with 1/f spectral decay of its stopband ripple (rather than constat level sidelobe levels). Why would we do this? Come by and listen, I’ll tell you! We will show you why and how and demonstrate advantages of this option.

In another example we will show how to design and implement FIR bandpass filters with different transition bandwidths on its low frequency band edge and its high frequency band edge. Now why would we do that? We do this to build proportional bandwidth filter banks in which bandwidth is proportional to band center frequency. In such a filter bank, the filter above my center frequency band, say at 4 kHz, has a higher bandwidth with a wider transition bandwidth and the filter below my center frequency band has a lower bandwidth and a narrower transition bandwidth. If we want a perfect reconstruction filter bank my center frequency band must match the transition bandwidth of the filters below and above my center frequency. Thus, my filter must have a lower transition bandwidth on its lower edge than it has on its upper edge. Can a filter do that? Yes! Why? Ask the hearing aid filter bank designer (or ask me)!