The last chapter is devoted to the relatively advanced topic of perfect-reconstruction filter banks. There has been much recent research literature regarding primarily critically sampled filter banks. This is appropriate in audio compression applications. This book, however, is not focused on compression applications, and therefore so-called oversampled filter banks are of primary interest. After introducing the basic terminology and properties of elementary perfect-reconstruction filter banks, it is shown that the polyphase representation of a filter bank can be recognized as an overlap-add representation, such as we develop in Chapter 8 and apply in Chapter 10. Thus, there is a unified view of polyphase filter banks and STFT processing.