Chorus maths question

Hi All,
I’ve been playing around with chorus design, and I’m trying to understand exactly how modulating a delay time affects the frequency range of the ‘vibrato’ produced. Particularly, I’m not getting why, when you decrease the delTime in the example below (keeping the width constant), the range of the ‘vibrato’ gets narrower. My maths is too rusty to work it out from first principles, and all the examples I’ve found just give you free parameters to tune by ear. How could one, say, calculate the parameters to get a particular frequency range for the ‘vibrato’? Thanks!

	var delTime =, 1/20, 1), width =,2);
	var snd =, 1, delTime *,1, 1/width, width));
	snd = snd!2;

Try this:

Effect Design, Part 2: Delay Line Modulation and Chorus

The paper is a tutorial intended to serve as a reference in the field of digital audio effects in the electronicmusic industry for those who are new to this specialization of digital signal processing. The effects presented are those that are demanded most often, hence they will serve as a good toolbox. The algorithms chosen are of such a fundamental nature that they will find application unbiquitously and often.

Author: Dattorro, Jon
Affiliation: CCRMA, Stanford University, Stanford, CA
JAES Volume 45 Issue 10 pp. 764-788; October 1997
Publication Date: October 1, 1997

[ Just do a search for the title… ]

There is a thread on chorus design here: Chorus effect design

Thanks @joslloand, that’s what I was looking for.