Introduction

In the exercises that follow, you will explore some of the effects of multirate processing using the system in Figure 1. The sample-rate compressor ( ↓D ↓ D ) in the block-diagram removes D-1 D 1 of every D D input samples, while the sample-rate expander ( ↑U ↑ U ) inserts U-1 U 1 zeros after every input sample. With the compression and expansion factors set to the same value ( D=U D U ), filters FIR 1 and FIR 3 operate at the sample rate F s F s , while filter FIR 2 operates at the lower rate of F s D F s D .

Figure 1: Net multirate system

Later, you will implement the system and control the compression and expansion factors at runtime with an interface provided for you. You will be able to disable any or all of the filters to investigate multirate effects. What purpose do FIR 1 and FIR 3 serve, and what would happen in their absence?

A second objective of this lab exercise is to introduce the TI-C549 C environment in a practical DSP application. In this lab, the C environment will be used to a limited extent to handle the basic sample input and output. The program flow and most of the implementation is to be done directly in assembly.

In future labs, the benefits of using the C environment will become clear as larger systems are developed. The C environment provides a fast and convenient way to implement a DSP system using C and assembly modules.