# [music-dsp] lfo-shape for a good chorus...

Bram de Jong Bram.DeJong at rug.ac.be
Fri Sep 8 09:41:02 EDT 2000

```> That looks like it would do the trick. You have a good idea to construct
> an LFO which receives an FM argument. All my LFO attempts have used a
> separate rate setting method.

??

I think this is what you mean:

http://www.smartelectronix.com/musicdsp/synthesis.htm#AK

<snip>
> Looks right-on to me. By the way, are your above examples pseudocode,
> csound, or something else entirely? Dunno much about csound or MatLab.

Pseudocode. Sort of.
My experimentation classes work like this.
I've created a large amount of slow-ish classes that do various DSP things
(oscs, filters, envs, ...). It's fun to experiment.
I could use CSound or STK, but writing your own is more fun...

> I'm not very good at math, but think you are correct. Hadn't realized
> (or perhaps forgot) that the code snip is actually integrating the
> triangle wave. Thanks for that insight.

Well, after thinking some more about it, the method you gave creates a
biased (only positive) parabolic wave...
Allso, you don't realy have good control over the depth!
Using a straigt-forward parabolic one does give you control.

> Would the pitch shape of a chorus delay line always be the derivative of
> the shape of the LFO which is used to offset the tap?

I think so (not realy sure though). Maybe you should check the Datorro
paper for the exact maths.

> And it would also explain that the integrated triangle (parabolic)
> modulation yields triangular pitch mod.

true.

> So perhaps Sine tap modulation simply yields Cosine pitch modulation?

seems logical. if the math is right...

> Back in the analog synth days, many players seemed to like triangle LFO
> vibrato better than sine LFO vibrato, so perhaps the slight visual
> difference in LFO shapes would be more obvious to the ear...

We are digital -> use a parameter!
Effect-users love control, so give them a parameter that gradualy changes
the wave from tri to sine/parabolic!

cheers,

Bram.

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