DSP Software and Basic Concepts in Digital Signal Processing

WHY STUDY DIGITAL SIGNAL PROCESSING?  Digital Signal Processing chips cover many applications.  For example, digital signal processing is needed for robot vision, image transmission and compression, pattern recognition, animation and digital maps just to name a few.  Digital processing is used to perform instrumentation, voice and speech processing, control of systems, telecommunications say for echo cancellation,

Consumer applications will include radar detectors, power tools, digital audio and TV, music synthesizer and educational toys.   Currently in development will be in my robotics section and will include videos describing these toys.  The robotic systems include:  Robosapien II, Robopet, Roboreptile, Vex Robotics, Boebot.  And the commercial application of iRobot.  iRobot uses AWARETM technology to navigate across the room 

Automotive application like engine control, vibration analysis, antiskid brakes,  navigation, digital ratio, and adaptive ride control or anything to make riding on an automobile an enjoyable experience. 

In terms of military applications digital signal processing can be used in communications, radar processing, image processing for target recognition, navigation, missile guidance and RF modems. 

TUTORIAL DESCRIPTION.  In this tutorial, we will cover the essential concepts and principles of digital signal  processing.  The topics of this tutorial will include:

•     Discrete-time signals
•     z-transforms
•     Discrete Fourier  Transforms
•     Finite Impulse Response (FIR)   - no feedback
•     Infinite Impulse Response (IIR) filters -  with feedback
•     Methods of digital filter design

TUTORIAL OBJECTIVES.  Some of the key concepts and objectives in understanding how digital signal processing works include the following:

•    Understand and process discrete-time signals and linear systems
•    Perform  digital signal operations in both time and frequency domains
•    Describe mathematically digital-time signals in the z-transforms
•    Apply the z-transform and inverse z-transform for signals and systems
•    Develop a discrete-time sequence from sampling a continuous-time signal, and then reconstruct the original signal. 
•    Use discrete-time techniques such as multi-rate, quantization and prefiltering
•   Design frequently selective IIR (Infinite Impulse Response) and FIR (Finite Impulse Response) digital filters
•   Perform Fourier techniques on discrete-time signals and using the discrete Fourier Transform

FLASH Demos.  See Flash-animated demos from Purdue University of continuous-time convolution, sampling, discrete-time convolution, FIR & IIR filter, FFT, pole-zero plots and frequency response, and spectograms.  

Filter Solutions.   An external website, Filter Solutions contains many different types of filters to choose from. Passive, Transmission Line, Active, and Digital IIR and FIR are all supported. See our FIR page for information about our FIR filters that are supported. Analog and IIR filters may all be quickly and easily delay equalized with our real time updates to all pass pole/zero manipulation.

Passive and active filters may be quickly and easily modified and reanalysed with our real time analysis feature. Finite Q may be included in the analysis.

Digital filters may be modified and analysis in real time for finite precision analysis.

Table one below lists the type of analog filters that are supported along with the parameters that are available for you to define.

M-Files.  The section provides categories of m-files for the powerful MATLAB program.  These files are intended to help you reduce your debugging time and encourage you to experiment more by varying the parameters and doing "what-if" thinking.  For example see if you can get a square wave sequence based on sinusoidal sequences. You can use any of the files to suit your style or programming needs.

DSP/Matlab Resources.  DSP and Matlab references of other web sites, especially for those who are new to Matlab. The web page will evolve as the course progresses during the next five weeks to provide better teaching projects and educational material.

MIT List of References

HST.582J/6.555J/16.456J
Signal Processing Resources
[ Course Resources | Probability ]

Overview:

New Links: Gibbs Phenomenon, Linear Algebra

This page describes several applets and on-line tutorials that cover some of the material presented in the first few weeks of the course. They are organized below according to lecture topic. All of the applets come from four main sites, listed here along with a general note about each. If you are aware of other web-based resources for learning this material, please let us know so that we can include them on the course website.

1. JHU Signals, Systems & Control Demonstrations - Has many different tutorials and applets available. In general the applets on this site are the best of those listed. If you are limited on time, go to this site.
    
2. Mississippi State Applets - Has a handful of applets with three that relate to this course. The applets are good at demonstrating various concepts, but do not include explanations. Therefore they are good for reviewing the material, but not a good place to start.
    
3. J-DSP - A very broad application where the user defines what signal processing is done through the setting up of a block diagram. Takes a little time initially to become familiar with the application, but can be very useful. A detailed description follows in its own section below.
    
4. RPI Links - Has a lot of applets, but most are not related to the early part of this course. Look to this site later for help on probability, which we plan to cover in a later handout.

• JHU Sampling - An OK applet that shows the results of changing the sampling frequency on the sampled signal and also the frequency magnitude.
   
• JHU Discrete-Time Frequency - A quick overview of the differences between continuous and discrete time frequency components.

• JHU LTI Systems and Convolution - An interactive lecture that contains a very good overview of LTI system properties and convolution. Includes an applet that allows the user to view the flip and shift method of continuous time convolution.
   
• JHU Discrete-Time Convolution - Discrete Time convolution applet that is easy to use and shows the flip and shift method. Not a lot of explanation provided.
   
• J-DSP - See below.
   
• Miss St Filter Design Tool - Under "user defined" option, you can input the filter coefficients and view the resulting magnitude and phase of the filter. Can also specify the filter type and frequency parameters, the applet will then produce the filter coefficients.
   
• Miss St Convolution Tool - Not much explanation. The user defines two signals and the resulting flip and shift convolution is shown.

• JHU Discrete-Time Fourier Series - Discrete Time Fourier Series (DTFS): applet that shows the relationship of DTFS coefficients, which are closely related to the DFT.
   
• JHU Continuous Fourier Transform - Continuous Time Fourier Transform (CTFT): Gives some properties of the CTFT, and allows the user to view the changes to the magnitude and phase of the transform given a change in amplitude, time shift, or derivative of the original signal.
   
• J-DSP - See below.

• http://web.mit.edu/6.555/www/matweb/demo.html - Interactive demonstration of spectral analysis developed for this course and used in Week 2 of Lab 1.
   
• Miss St Spectrum Analysis Tool - Applet graphs magnitude and phase of CTFT after a signal and window are defined. Helps to see the differences between various types of windows, but not real easy to use.

Java Digital Signal Processing (J-DSP) is an on-line DSP simulator. The program is very broad and does not target a specific topic like the other tutorials. But it can be very useful for filter design, FFT evaluation, and even speech analysis. JDSP does take a little bit of time to get used to, however.

Filter Example:

For a quick example we can design an FIR or IIR filter. The figure below is the main screen of the JDSP editor, refer to it while reading the example below.

The first step is to skim over the General Information tutorial found under the exercises heading on the main page. This exercise goes through the same example as below and explains in more detail how to attach and manipulate blocks, etc.

1. At the main page click on "start J-DSP" under the "J-DSP Main" header to get started.
    
2. First we need an input signal. To do this, simply click on [Sig. Gen] on the left side of the page and then click on the white area to place a sig. gen. block. Clicking on this box will bring up another window where you can define a sequence or select a standard sequence such as a sine or exponential.
    
3. Next we place a filter block on the white area and connect our input signal to it with an arrow. Note that we have not defined any part of the filter, and for now it is just passing the input signal through. To adjust our filter we need to change coefficients.
    
4. Add a coeff. Block to the work area and attach it to the filter block as shown. Clicking on the coeff. block will bring up another window where the a and b coefficients can be entered to define an FIR or IIR filter.
5. The Freq-Resp. block attached to the filter block shows the magnitude and phase of the filter. Click on this block and keep the resulting window open as you adjust the coefficients. You can then watch how the magnitude and phase change while changing the coefficients. Remember to press update when you change the coeff. block, then JDSP will update all blocks simultaneously.
6. By adding a plot block to the output of our filter we can view the output sequence. Clicking on the plot block brings up a window where the filtered signal is plotted.

The three blocks at the bottom of the figure are a quick way to view the FFT of a given signal. Simply clicking on the plot block will allow the user to view the magnitude and phase of the fft.

To get access to the Digital Signal Processing Course, please contact me at 719-963-5873 or john@e-liteworks.com. 

Also please check this lens monthly to see updates on the latest resources.

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