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Lab #9

FATIMAN JINNAH WOMEN UNIVERSITY RAWALPINDI

Digital Signal Processing

Lab#9

Digital Filter Designing using FDA Tool; Introduction to FVtool

Objectives

To get acquainted with the types of filters

To get acquainted with filter design process

To get acquainted with FDA tool

To observe the relation b/w order of the filter and the

degree of its cutoff To get acquainted with FV tool

Introduction:

The filters may be broadly classified as follows:

1. Low-pass filters

2. High-pass filters3. Band-pass filters4. Band-stop filters

The typical responses of these filters are shown below:

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0 5 10 15 20

-60

-50

-40

-30

-20

-10

0

Frequency (kHz)

Magnitude(dB)

Magnitude Response ( dB)

Low Pass Filter (Cutoff = 4kHz)

0 5 10 15 20

-70

-60

-50

-40

-30

-20

-10

0

Frequency (kHz)

Magnitude(dB)

Magnitude Response (dB)

High Pass Filter (Cutoff = 6kHz)

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0 5 10 15 20 25 30

-60

-50

-40

-30

-20

-10

0

Frequency (kHz)

Magnitude(dB)

Magnitude Response (dB)

Band Pass Filter (24 28 kHz)

0 5 10 15 20 25 30

-70

-60

-50

-40

-30

-20

-10

0

Frequency (kHz)

Magnitude(dB)

Magnitude Response (dB)

Band Stop Filter (24 28 kHz)

Alternatively, they may also be classified according to theirresponse type as:

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1. FIR Response is time limited2. IIR Response is not limited in time

FDA tool is the filter design and analysis tool in MATLABwhich is used for the design and analysis of FIR or IIR filters.It may be opened by simply typing the following commandin MATLAB command window:

>>fdatool

Alternatively, it may also be opened by following the methodgiven below:

1. Go to MATLAB Start2. Point to Toolboxes3. Point to Filter Design in the sub menu4. Click on Filter Design & Analysis Tool (fdatool)

Following is the self-explanatory diagram of FDA toolinterface:

Filter Design and Analysis Tool - Interface

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Following are some of the parameters considered duringfilter design process in FDA tool:

fstop Start of stop band

fpass End of pass band Apass Magnitude (dB) by which pass band

frequencies will be attenuated Astop Magnitude (dB) by which stop band frequencies

will be attenuated fs Sampling frequency of the filter

Must be greater than twice the max filterfrequency

Order Order of the filter

Think of order as the measure of how much processingpower our digital filter will require to be implemented.Hence,

1. Sharper the cutoff, higher the order2. Higher the fs (not fstop), higher the order

Task1: Verify the above statements in your in labtasks in FDA tool

FV tool is the Filter Visualization tool in MATLAB and you canuse it to analyse your filter response in details. It may beopened from FDA tool by first designing a filter and then

opening this tool from ViewFilter Visualization Tool. Theinterface of this tool is shown below:

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FV Tool Interface

In-Lab Tasks

1. Design a minimum order low pass filter to suppress all

frequencies above 4kHz. Mention the application of such afilter in your reports

2. Design a minimum order high pass filter to pass allfrequencies above 6kHz. Mention the application of such afilter in your reports

3. Note: Observe that there is a guard band of 2kHzbetween 4kHz and 6kHz. Exploit it.

4. For a frequency range of 24kHz 28kHz, design bandpass and band stop filters resp.

5. Use FV tool to show all the above results