Multirate Filtering: Introduction

Module by: Douglas L. Jones, Swaroop Appadwedula, Matthew Berry, Mark Haun, Jake Janovetz, Michael Kramer, Dima Moussa, Daniel Sachs, Brian Wade

Summary: A sample-rate compressor removes (D-1) of every D input samples. A sample-rate expander inserts (U-1) zeros after every input sample.

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

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?

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