# FAQ

## CORDIC FAQ

### 1. Basics

#### 1.1 What does "CORDIC" mean?

COordinate Rotation DIgital Computer. (Doesn't help much, does it?!)

## Interpolation

### 3.1 Basics

#### 3.1.1 What are "upsampling" and "interpolation"?

"Upsampling" is the process of inserting zero-valued samples between original samples to increase the sampling rate. (This is called "zero-stuffing".) Upsampling adds to the original signal undesired spectral images which are centered on multiples of the original sampling rate.

## Resampling

### 4.1 Basics

#### 4.1.1 What is "resampling"?

"Resampling" means combining interpolation and decimation to change the sampling rate by a rational factor.

## Decimation

### 2.1 Basics

#### 2.1.1 What are "decimation" and "downsampling"?

Loosely speaking, "decimation" is the process of reducing the sampling rate. In practice, this usually implies lowpass-filtering a signal, then throwing away some of its samples.

"Downsampling" is a more specific term which refers to just the process of throwing away samples, without the lowpass filtering operation. Throughout this FAQ, though, we'll just use the term "decimation" loosely, sometimes to mean "downsampling".

## IIR Filter Basics

### 1. IIR Basics

#### 1.1 What are IIR filters? What does "IIR" mean?

IIR filters are one of two primary types of digital filters used in Digital Signal Processing (DSP) applications (the other type being FIR). "IIR" means "Infinite Impulse Response".

## Multirate Basics

#### 1.1 What does multirate mean?

Multirate simply means "multiple sampling rates". A multirate DSP system uses multiple sampling rates within the system. Whenever a signal at one rate has to be used by a system that expects a different rate, the rate has to be increased or decreased, and some processing is required to do so.

## The Fast Fourier Transform is one of the most important topics in Digital Signal Processing but it is a confusing subject which frequently raises questions. Here, we answer Frequently Asked Questions (FAQs) about the FFT.

### 1. FFT Basics

#### 1.1 What is the FFT?

The Fast Fourier Transform (FFT) is simply a fast (computationally efficient) way to calculate the Discrete Fourier Transform (DFT).