Course Description

Goals of the Course

In this course we learn how the basic structure of sound perception affects the useful ways of processing sound through digital computations. The focus is on basic synthesis techniques, rather than on signal analysis, or on special applications of synthesis such as music or speech.

Prerequisites

Introductory computer programming (ComSci 105/106 or 110/111 or 115/116 or equivalent), basic knowledge of trigonometry, calculus, and complex numbers.

Required Equipment

Stereo headphones with small jack plug. They can be cheap. Headphones from portable music machines suffice. A long wire or extension cord is essential if you work with computers that have the headphone connection in the back.

Electronic Communications

We use three forms of electronic communication in CS221: shared files, the World Wide Web (WWW), and electronic mail. Use of these forms of communication is required.

• You must provide a publicly readable directory named CS295 in your home directory on the CS computer file system. I will collect links to these in my own public class directory: /stage/current/CS295/Class_members. Store all online materials that you develop for this class in your public directory, so that we can share work. I also encourage you to develop your own WWWeb materials.
  
  
• I will also provide course materials in a form accessible through WWW, at the URL http://www.classes.cs.uchicago.edu/classes/current/CS295/. The recommended tools for viewing this material are NetScape from graphics terminals and Lynx from character terminals.
  
  
• There is a public class discussion, consisting of comments attached by students and the instructor to various online course materials. All questions and comments that are not personal or confidential should be added to this discussion, so that everyone can benefit from them.
  
  
• Personal discussions, particularly about grading, and requests for appointments, may be addressed to me by electronic mail at odonnell@cs. These will normally be the only types of correspondence that should be made by electronic mail.

You must check for new information in the WWW materials at least three times a week: on Tuesday, Thursday, and the weekend. I recommend that you check it daily, particularly the class discussion.

Topics

The sequence of topics in this course is organized around different techniques for synthesizing and/or manipulating sound, roughly increasing in sophistication and power.

• Continuous sound, sampling, and quantization. Sound is naturally represented as a continuous function from a real number representing time, to a real number representing the pressure of the air at a certain point, or perhaps the flow. For some purposes, it is better to regard sound as a continous function from time to a complex number, whose real part is some physical value such as pressure and whose imaginary part is a related value such as flow. In either case, computer models of sound digitize the continuous function in two crucial ways: (1) they sample the function at a discrete set of input time values, and (2) they quantize the output pressure/displacement values into fixed-point or floating-point approximations. Each of these forms of digitization limits the fidelity with which we can represent a given sound.
  
  
• Naive sound processing. An obvious approach to sound synthesis is to record real sounds, and manipulate them computationally. We study some simple computational ways of manipulating the speed, duration, and pitch of recorded sounds, and discover their limitations.
  
  
• Additive synthesis with enveloping. Steady sounds may be constructed by adding simple periodic components, usually sine waves. Then, these steady sounds may be shaped by amplitude modulation with envelope functions that control the attack and decay. We discover what sorts of sounds can and cannot be constructed conveniently in this way.
  
  
• Filtering. A filter modifies a sound. We explore the control of sound by providing different sorts of sound inputs to a variety of filters.
  
  
• Special topics. If time permits, which it probably won't, we will explore some more specialized topics, such as frequency modulation, reverberation, or sonic imaging.

• [A.]Sound perception. We develop an abstract and approximate understanding of the way the ear analyzes vibrations of the air into component frequencies. We discover the shortcomings of overly simplistic descriptions of sound perception.
  
  
• [B.]Transform theory. We review the Fourier Transform as a mathematical tool for analyzing sound into component frequencies. We see how some (but not all) of the shortcomings of the Fourier Transform are corrected in the Z Transform and the Wavelet Transform.
  
  
• [C.]Experiment. We make a lot of noises and listen to them. This is the fun part.

Class Work and Grading

The main work for the course is a project, involving the creation of interesting sounds simulating notes played by a musical instrument. All project work is shared cooperatively among all students. I will grade your project, not on the grounds of the program(s) that you write, but on a 1-hour private interview in which you demonstrate and explain the results of the project. You may use anyone's results in your interview (with attribution, of course), but I will grade you on how well you explain the results in terms of the ideas discussed in class.

You may schedule a preliminary project interview at any time during the quarter and I will tell you how you are doing so far.

There may or may not be a small amount of written homework and quizzes. If there are, they will constitute a minor part of the course work.

Grading Scheme

The grading for this course is quite flexible and rather subjective. I will give credit for all sorts of contributions to the class work if I can recognize them and evaluate them. You may emphasize your strongest talents, and avoid the areas in which you feel weaker. For example, a strong programmer may contribute by fixing up software, while a weak programmer may contribute by providing careful critiques of synthesized sounds. If you want credit for your contribution, make sure that I know what it is.

You may negotiate your own individual grading scheme, based on your particular contributions, at any time. Absent an individual scheme, I will evaluate your work by the following default:

Project interview	80%
Online discussion participation	20%

Both of these categories depend on my subjective evaluation. If we choose to do some written work, I will reallocate 5-10% from the interview and participation.

Student evaluations from previous years

Copyright Michael J. O'Donnell <michael_odonnell@acm.org>. Licensed for free use.
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