Assignment 7: Recursive Comb Filters

One of the more unusual applications of delay lines is the creation of resonators, or (more technically) recursive comb filters. This is a fairly old computer music technique, exemplified in music by Risset (Sud), Lansky (Now and Then [5:55 on], Word Color), among others.

In keeping with this heritage, all the computer music programs derived from the early “Music N” languages have comb filter unit generators, which make it easy to specify resonated pitches and form chords with them. Modern DAWs are not normally well set up for this, but it’s still possible to create recursive comb filters with any delay effect that allows precise specification of short delay times and feedback. Some plugins offer resonators (e.g., in GRM Tools). Max includes two versatile objects that perform comb filtering: comb~ and teeth~. A few of the Max4Live devices are also relevant. With many of these tools, you will have to figure out how to compute the delay time that will give rise to a specific pitch you want.

For this assignment, choose a brief (c. 20-30 seconds) recording of speech, and use comb filters to resonate specific pitches, possibly including the production of chords. You might want to make use of low-pass filters to tame the buzzy comb filter sound some of the time. You can record your own voice, or use some other speech sound file you have, or make use of the poems we assign in Z361 (IU network only).

To make the sound, choose RTcmix, Max 7, or any of the DAWs we use in 302 (DP, Logic, Live — even Audition, in Multitrack mode, can work). Submit a zipped folder of whatever files are required to play your project.

One reason to do an assignment like this, apart from learning about comb filters, is to consider the strengths and weaknesses of the different tools we use. Think about this while doing your assignment.

Copyright ©2017 John Gibson