Homework 3: Frequency Modulation & Auditory Streaming

due on 11/8 (Tue) in the Homework Factory.

Overview

From this stage in the course onward 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.

Self-quiz

Refer to the earlier readings for background on both subjects.

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?
Auditory Scene Analysis
  1. The auditory cue of "synchronized changes" (the Gestalt principle common fate) helps us identify sound sources. Give an example.
  2. Harmonic spectra will fuse together and sounds from a particular location might fuse together better, if they < fill in the blank > exactly together.

Background and Tutorial Lab

Fig. 6.14 from CMT

The block diagram to the right (Figure 6.14 in the Computer Music Tutorial) 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. In music, often your mind groups objects for you over time - hence you 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 create an auditory illusion that you like - shoot for one that maximally segregates the voices: hw3-starter.ck. 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.

We'll be listening to hear the effect of a slow note sequence blossoming into illusory polyphonic lines as it increases speed. In addition, make it into a musical study in which the illusion is present but it's not the only thing going on. 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. Concoct at least one big musical change (your choice of what that is, but it should be obvious to the listener) and 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. Convert the final 4 mono .wav files to a combined 4-channel ambisonic file.

Submit to the Homework Factory an HTML file titled hw3.html that includes the following:

  • Links to all ChucK files you used and wrote in your composition.
  • A button to play your ambisonic file.
  • A short description of how your piece and your thoughts behind your composition study.