Linear and Generalized Linear Phase

In many applications, it is desirable to design filters that affect the magnitude of the Fourier transform of the input in some way – for example, by attenuating certain frequency components, while affecting the phase as little as possible. Unfortunately, for causal systems, it is not possible to achieve zero phase. Instead, as a design goal, we can try to make the phase as close to linear as possible. We saw in previous lectures that the negative derivative of the phase, i.e., the group delay, indicates how frequency components of the input are delayed.