Homework: Auditory Streaming Illusion
- Out: Oct 5, 2021 Tuesday
- Due: Oct 12, 2021 Tuesday
Objective and Overview
Make a short (1~2 min.) version of the auditory streaming illusion explained and demonstrated here. We'll be looking for solutions that depart from the starter code in creative ways. For this study, you'll use FM synthesis to demonstrate the perceptual phenomena of "auditory streaming." Run the starter code example, play with it to understand how it works and then invent replacements and variations which fulfill the assignment. Your Library/Web/220a/hw2/index.html
page should reference files in your Library/Web/220a/hw2/
directory.
Key Steps
- Make a local directory
hw2
with anindex.html
file and subdirectories to contain media (media
) and ChucK code (ck
). - Install Chuck from here by following the download links for your operating system. Practice with some examples to get the hang of running it.
- Download and run the starter ChucK code locally using ChucK.
- As it plays it will also be writing a sound file. The output is set to
../media/test.wav
but can be changed in the code. - Modify the code, create you own inventions and collect them as sound files.
- Mix the inventions into a single composition.
- Upload the project to a new homework directory named
hw2
on your CCRMA web space.
Background
Listen to Al Bregman's demonstration of the illusion. 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 when more closely spaced.
In this assignment, you'll be using the FM instrument from the starter code to create multiple different sound sources that then perceptually group together when played in closer timing.
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 starter code 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.
This block diagram from John Chowning's The Synthesis of Complex Audio Spectra by Means of Frequency Modulation shows a typical simple FM instrument.
Consideration
The illusion can be created with any radically-enough timbral differences. Here we are restricted to contrasts within those parameters belonging to simple FM.
- Loudness
- Carrier / Modulator frequency ratios
- Envelopes on carrier and modulator amplitude and frequency
- Left / right panning
Collect variations as different sound files. Make some contrasting versions.
Composition
Mix the soundfiles you've produced in an audio editor (for example, audacity). Try out:
- horizontal composition: assemble a sequence of soundfiles (tracks)
- vertical composition: layer multiple tracks
- (optional) explore editor effects, for example, chorusing
- (required) output the final mix as a single sound file and save in hw2/media/
...or use Chuck for Composition (an optional extra)
Rather than manually compose the final mix in an audio editor, try automating your audio edit decisions in Chuck. The progression of examples in this repository illustrates how Chuck's time management and processes are scheduled. Soundfile "clips," like video clips, are arranged by functions defined in the last example in the repository.