In this and the next chapter we will discuss in detail only the second step, which is the conversion of specifications into a filter description.
In many applications like speech or audio signal processing, digital filters are used to implement frequency-selective operations. Therefore, specifications are required in the frequency-domain in terms of the desired magnitude and phase response of the filter. Generally a linear phase response in the passband is desirable. In the case of FIR filters, it is possible to have exact linear phase as we have seen in Chapter 6. In the case of IIR filters a linear phase in the passband is not achievable. Hence we will consider magnitude-only specifications.