Use complex multirate filters in the implementation of Digital Down-Converters (DDC). The DDC is a key component of digital radios. It performs the frequency translation necessary to convert the high input sample rates typically found at the output of an analog-to-digital (A/D) converter down to lower sample rates for further and easier processing. In this example, we will see how an audio signal modulated with a 450 kHz carrier frequency can be brought down to a 20 kHz sampling frequency. After a brief review of the conventional DDC architecture, we will describe an alternative solution known as Intermediate Frequency (IF) subsampling and we will compare the respective implementation cost of these two solutions. This example requires a Fixed-Point Designer™ license.