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Project 1 - Sound Blaster!

Due: Friday January 13

  • Electronic copy due at Noon (link) Read directions before turning in! Bad submissions may lose points!
  • Hand in hardcopy (code & written questions) in class (details to come)

Make sure you go through General Policies, Grading Policies and Programming Guidelines before you begin working on the project. In particular, note that the writeup you turn in is worth a substantial portion of the grade!



The purpose of this project is to implement a Stack ADT in the two most common ways, a static array and a linked list.

Your Stack implementation will be used to do sound manipulation, namely reversing a sound clip. This tool was used by musicians including the Beatles, Jimi Hendrix and Ozzy Ozbourne, although it seems to have fallen out of favor in recent years. "But wait," you say, "CSE 143 never taught me how to work with music..." Don't worry! Most of the hard work has already been done.

The Assignment

You will write a program that will take a sound file in the .dat format (explained below), and output another .dat sound file which is the reverse of the first. We provide you with a class Reverse which reads in a .dat sound file, puts the sounds values on a stack, pops them off in reverse order, and puts these reversed values in a new .dat sound file. We've also provided you with a DStack interface, which defines a stack that holds double values. Your first job is to look over these files and become familiar with them.

Now for the work! You need to provide two stack implementations, one using an array and the other using a linked list. They should be called ArrayStack and ListStack, respectively. They should implement the interface DStack, which we provide to you. Once you provide this implementation, Reverse should work and create backwards sound files. It shouldn't take more than a page or two of code to provide the implementation. Your array implementation should hold around a million elements. The Reverse program takes 3 arguments. The first is either array or list, and specifies which implementation to use. The next two are the input and output .dat files (you need to provide the .dat extension). Running the program will depend on your system; from the command line it will look something like the following.

java Reverse list in.dat out.dat
In an IDE there is usually a dialog for setting program parameters which contains a field for the program arguments.

Read the section on Digital Sound to learn how to create a .dat file. To get you started, we've created a .dat file here.

For details on what to turn in for this assignment and how, read the section on Logistics. For a quick reminder of how interfaces work in Java, see Java Reminder.

In addition, answer the following questions and provide the answer in your writeup.

Writeup Questions

  1. Who/What did you find helpful for this project?
  2. How did you test that the final program is correct?
  3. The file secret.wav is a backwards recording of a word or short phrase. Use sox (or another converter) and your program to reverse it, and write that as the answer to this question.
  4. Did you use any classes from the Java framework or other class library? (Remember, as stated in the programming guidelines, if the answer to this question is anything other than "no", you're going to get a low score on this project!)
  5. What happens if you exceed the maximum size of the array implementation of DStack? Can you think of other ways to handle this case, if you were allowed to change DStack.java and Reverse.java? Be specific: refer to particular lines of code that would change, list any exceptions you would add and who would throw them, describe who catches any such exceptions and how they are handled, etc. Refering to comments you have inserted in your code is the best way to do this.
  6. Describe an input that would cause Reverse to behave differently when run with the array implementation than with the list implementation. Describe how the outputs differ in these two cases (note that your program should produce output files in both of these cases, rather than fail with an uncaught exception).
  7. Let's pretend that, instead of a DStack interface, you were given a fully-functional Queue class. How might you implement this project (ie, simulate a Stack) with one or more instances of a Queue? What is the runtime of a single top or pop operation?
  8. In the previous question, what trade-offs did you notice between a Queue implementation of a Stack and your original array-based implementation? Which implementation would you choose, and why?
  9. A description of how your project goes "above and beyond" the basic requirements (if it does).
  10. What did you enjoy about this assignment? What did you hate? What could you have done better?
  11. Any other information you would like to include.

Going Above and Beyond

The following list of suggestions are meant for you to try if you finish the requirements early. Recall that any extra-credit points you earn for these are kept separate from your assignment score and will be used to adjust your grade at the end of the quarter, as detailed in the course grading policy.

  • Change the array implementation to grow when it becomes full.
  • Try implementing the Karplus-Strong algorithm (to generate "reverb" sounds). A description of this algorithm is available here.
  • Assuming that your .dat input file contained a single note, try writing a program which will output a single-octave scale beginning at that note. Would the notes of an "evenly spaced" scale grow logarithmically, linearly, polynomially, or according to some other function?

Logistics for Project 1

  • The files we have provided for you:
  • It may be useful for you to create some short .dat files by hand to aid testing.
  • Each file you turn in should have your name at the beginning. All text files should have your name on the first line; your name should appear in a comment at the beginning of all source code you turn in.
  • You cannot use any classes from the Java framework. The rule of thumb is that you should not use the import statement at all. The Reverse class needs to import some things, but your classes do not. You will lose half of your score if you do!
  • Electronic Turnin: You should turn in the following files. Remember to put in your name!
    • ArrayStack.java. Your array should hold around a million elements.
    • ListStack.java
    • README.txt, your writeup, containing the answers to each assignment question.
    • Any extra credit, in a separate directory or enclosed zip file.
    These files should all be put into a zip archive. Note that you do not turn in either Reverse.java or DStack.java. This means you shouldn't change them, either---your code must work with the original, unmodified versions.

    Your extra credit may include a modifed Reverse.java, but because you've included it in a separate directory we'll be able to compile & grade your regular assignment without touching your extra credit. If you don't segregate your extra credit you probably won't receive credit for it!Hardcopy Turnin: In class, turn in hardcopies of each file turned in electronically. Remember your name!

    • ArrayStack.java
    • ListStack.java
    • README.txt, containing the answers to the assignment questions. This should be a text file (like from notepad), not a Word document or anything else.
    Please make sure you have printed these files in a legible manner. If it's difficult for your TAs to read or grade them, you will loose points.
  • You may discuss the assignment with others in the class, but your solution must be entirely your own work!

How Digital Sound Works

We will view sound as a continuous function of time from the positive real numbers (time) to the interval [-1.0, 1.0] (amplitude). Since a computer can't "hold" a function defined on the reals, we have to approximate the function. We do this by measuring (or "sampling") the sound several thousand times per second.

This process is called "Analog to Digital Conversion", or ADC. The number of times per second the sound is sampled is called the sample rate and is measured in Hertz. For example, CDs are recorded at 44100 samples per second, or 44.1kHz. Wait a minute! Is this the right class? I thought this was CSE326.


Yes, this is CSE326. The only sound file format you need to know about is the .dat format described below. You don't even have to know very much about that either, as we're giving you the code that reads and write that format. In order to play sounds you produce, you need a way to convert the .dat file into a format that common media players (Windows Media Player, winamp, RealPlayer, etc.) understand. We'll describe one way to do it below; however, you're free to use any converter you can find.

There is a windows version of sox available at SourceForge. It seems to work well, but download and run at your own risk. It is also a command-line program and works in the same way as the UNIX version described below.

sox is a UNIX command-line utility whose name stands for "SOund eXchange". It allows you to convert between many different sound formats including .wav, .au, etc... In particular, sox allows you to convert to and from .dat sound files. .dat files are cool because they are human-readable, text-based, sound files. Note that you will need to perform this conversion to answer one of the writeup questions.

The general strategy is as follows.

  1. Take a .wav sound file of your choosing (e.g. secret.wav) This sound shouldn't be longer than a couple seconds, or your program will run out of memory.
  2. Convert it to a .dat file: sox secret.wav secret.dat
  3. Manipulate it with the program you will write: java Reverse secret.dat secret-revealed.dat
  4. Convert it back to .wav file: sox secret-revealed.dat secret-revealed.wav
  5. Listen to it! (Use your favorite sound player.)
sox has been installed in the cse326 course directory. In order to use it conveniently on the command line, you should put it in your path by doing something like the following: export PATH="/cse/courses/cse326/06wi/bin:$PATH". See the Unix tutorials on the very useful ACM Tutorials page for more help on Unix.

If you get a command not found error when trying to do the export mentioned above, it's probably because you're in the tcsh shell. Given your TAs unfamiliarity with that shell, the easiest thing to do is type bash to enter the bash shell, at which point the export command should work as advertised.

That's all there is to it! But before we get too excited, let's first explain...

The .dat File Format

The .dat file format starts with one line describing the sample rate of the sound file. This line is required. The rest of the file is composed of two columns of numbers. The first column consists of the time (measured in seconds) when the sample was recorded, and the second column contains the value of the sample, between -1.0 and 1.0. Here is the beginning of a sample .dat file. Notice that the numbers in the first column increase by 1/44100 each step. This is because the sample rate is 44.1kHz.

; Sample Rate 44100
0             0
2.2675737e-05 0
4.5351474e-05 0
6.8027211e-05 0
9.0702948e-05 0
0.00011337868 0
0.00013605442 0
0.00015873016 0
0.0001814059  0
0.00020408163 0

Here is the same file, a little deeper on:

0.22693878    -0.0062561035
0.22696145    -0.0043945312
0.22698413    -0.0068664551
0.2270068     -0.011566162
0.22702948    -0.014556885
0.22705215    -0.014541626
0.22707483    -0.012191772
0.22709751    -0.012390137
0.22712018    -0.014541626
0.22714286    -0.01449585
0.22716553    -0.014770508
0.22718821    -0.015701294
0.22721088    -0.012954712
0.22723356    -0.012710571
0.22725624    -0.018157959
0.22727891    -0.01914978
0.22730159    -0.014572144
0.22732426    -0.012237549
0.22734694    -0.012435913
0.22736961    -0.010818481

Note that for this assignment, you shouldn't have to deal much with the .dat file yourself, as the provided Reverse.java does all the lifting for you. All you have to do is implement the stacks. We are telling you the format because it will be helpful for you to write a short file by hand to run, to verify if your program works.

Java Reminder

For this assignment you will need to instantiate an interface, DStack, in two different ways. The DStack interface defines a simple stack:
interface DStack {
  boolean isEmpty();
  void push(double d);
  void pop();
  double top();
To implement this interface, write a class as follows.
class ArrayStack implements DStack {
  public ArrayStack() {
    // Your constructor

  public boolean isEmpty() {
    // Your isEmpty()

  public void push(double d) {
    // Your push()

  // continue with the rest of the functions,
  // along with any member variables, etc.
The ListStack class should be defined similarly.


Like many assignments, this has been passed down to us through the vaporous mists of time. Among all our fore-bearers, we would especially like to thank Ashish Sabharwal, and Adrien Treuille and his Data Structures professor, Timothy Snyder.

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