CHAPTER 7 Decimation and Interpolation In this chapter, we discuss decimation and interpolation. Decimation is the process of reducing the sample rate F s in a signal processing system, and interpolation is the opposite, increasing the sample rate F s in a signal processing system. These processes are very common in signal processing systems and are nearly always performed using an FIR filter. First, why are sampling rates changed? The most common reason is to ease the interface of the digital signals to the outside environment. As we saw in previous chapters, signals have a frequency representation, and this frequency representation must be less than the Nyquist frequency, which is defined as F s /2. This sets a lower bound on F s . The amount of hardware or software processing resources is normally proportional to F s , so we usually want to keep F s as small as practical. So while there is no upper bound on F s , it is usually less than 10Â the frequency representation of the signal. A minimum F s is needed to ensure the highest frequency portion of the signal does not approach the F Nyquist frequency. > In some cases, there are advantages to highly oversampling a signal, where F s > F signal . One