Homework 3: Auditory Streaming Illusion, Frequency Modulation & Chuck Clips

due on 10/31 (Wed) in the Homework Factory.


We'll be looking for homework that departs from the starter code in creative ways. For this homework study, use FM synthesis to demonstrate the perceptual phenomena of "auditory streaming." Run the starter code examples, play with them to understand how they work and then invent replacements and variations which fulfill the assignment. Your Library/Web/220a/hw3.html page should reference files in your Library/Web/220a/hw3/ directory.


Refer to the earlier readings for background on both subjects.

Auditory Scene Analysis
  1. Harmonic spectra will fuse together and sounds from a particular location might fuse together better, if they
    < fill in the blank > exactly together (the < fill in the blank > principle of common fate).
  2. Demo of perceptual continuation, aka the < fill in the blank > principle of good continuation.
FM Synthesis
  1. When will FM synthesis generate inharmonic spectra?
  2. As a rule of thumb, what is the number of significant sideband pairs in FM?

Background and Tutorial Lab


The block diagram to the right (from John Chowning's article The Synthesis of Complex Audio Spectra by Means of Frequency Modulation) shows a typical simple FM instrument.

Grab the starter code and study how it implements a version of this instrument in ChucK: hw3-starter.ck.

Likewise, visit the project presented in the coreLectureSequence "ck-clips" and study how it borrows the notion of movie-style "clips" and abstracts these into units to compose with: ck-clips.

Composition Study - Auditory Streaming

The phenomenon of auditory streaming is a fascinating one. It is the process by which your mind groups information into independent objects and suggests sources. In music, often your mind groups objects for you over time - hence your being able to listen to a band and follow the lines of the different instrumentalists somewhat independently! Here's a visual analogy - the mind groups together the objects for you:

In this assignment, you'll be using the FM instrument from the lab above to create multiple different sound sources, that then perceptually group as coherent sources.

Download the starter code and edit it to create an auditory illusion that works convincingly - shoot for one that maximally segregates the voices when played at a fast tempo. The effect depends on differentiation of sonic parameters. Choose your own dimension(s) for the effect e.g., timbral, spatial and/or envelope qualities. Tune the effect by ear and make it different from the start code example. Then, re-program it in the form of a "clip" as described in ck-clips so that one "clip" creates a single (monophonic) streaming example. Like the starter code example, you should hear the effect of a slow note sequence blossoming into illusory polyphonic lines as it increases speed.

For the homework, make a musical study in which the illusion is present but it's not the only thing going on.

  1. Invent some other FM-based sounds to go with it and layer them in as clips. These don't need to be streaming illusions, they could be e.g., a melody, a rhythm, an ambient layer, etc.
  2. Concoct at least one big musical change (your choice of what that is, but it should be obvious to the listener)
Shoot for a total duration of around 1 minute.

As with HW2, do your work in four channels, even if you don't use all of them all the time. Take advantage of sound arriving from different angles and if you want to, use the spatial dimension as one of the "differentiators" that creates the streaming illusion. The final 4 mono .wav files should be deposited in your Library/Web/220a/hw3/ directory and played from your Library/Web/220a/hw3.html page. Have a look at Chris Chafe's hw3 in the Homework Factory and "save link as" if you'd like to work from a copy of it.

Submit the page to the Homework Factory as before and include the following:

  • Links to all ChucK files you used and wrote in your composition.
  • A button to play your 4-channel composition study.
  • A short description of your thoughts behind the study.