Transfer function in desmos sheet (Hjälp needed)

DSP, Plug-in and Host development discussion.
juha_p
KVRian
542 posts since 21 Feb, 2006 from FI

Post Fri Apr 05, 2019 7:02 am

Are there desmos sheets with (various) transfer functions available anywhere (web)?

I would like to compare 1st order LPF (based on MZT method) against its analog (A) version. Here's my sheet: https://www.desmos.com/calculator/yzel8sdbq7
and here's the Wiki page for MZT I'm trying to enter: https://en.wikipedia.org/wiki/Matched_Z ... orm_method

Any help is highly appreciated.

mystran
KVRAF
5278 posts since 12 Feb, 2006 from Helsinki, Finland

Re: Transfer function in desmos sheet (Hjälp needed)

Post Fri Apr 05, 2019 2:31 pm

Doing this in desmos is rather inconvenient [edit: as in "lots of manual trigonometry"], since you need to evaluate the responses (complex magnitude and phase, depending on which one you want to plot) on the imaginary axis of the s-plane and unit circle of the z-plane and as far as I can tell desmos doesn't know about complex numbers.
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matt42
KVRian
1106 posts since 9 Jan, 2006

Re: Transfer function in desmos sheet (Hjälp needed)

Post Fri Apr 19, 2019 4:27 am

Hi Juha_p. Its been awhile since your post. Did you manage to find a solution?

juha_p
KVRian
542 posts since 21 Feb, 2006 from FI

Re: Transfer function in desmos sheet (Hjälp needed)

Post Fri Apr 19, 2019 6:52 am

Hi. I didn't find a solution I would have prefered but managed to calculate the value at selected point (as like done for s-plane (value A there in mu desmos sheet)) using common formula based on this thread.

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Music Engineer
KVRAF
3809 posts since 8 Mar, 2004 from Berlin, Germany

Re: Transfer function in desmos sheet (Hjälp needed)

Post Fri Apr 19, 2019 7:19 am

mystran wrote:
Fri Apr 05, 2019 2:31 pm
as far as I can tell desmos doesn't know about complex numbers.
maybe then geogebra could be used as alternative:
https://www.geogebra.org/graphing?lang=en

disclaimer: i'm not very familiar with it, but entering something like "w = exp(i*pi)" gives you the correct result of -1 + 0i, so at least, it can deal with complex numbers
Image

matt42
KVRian
1106 posts since 9 Jan, 2006

Re: Transfer function in desmos sheet (Hjälp needed)

Post Fri Apr 19, 2019 9:29 am

Don't know if it's any use, but you mentioned MZT vs analog 1 pole LPF. Here's how I did it in desmos: https://www.desmos.com/calculator/yjbvjyok02 Did it on my phone, so possibly error prone.

Music Engineer, I'll take a look at geogebra, thanks

matt42
KVRian
1106 posts since 9 Jan, 2006

Re: Transfer function in desmos sheet (Hjälp needed)

Post Sat Apr 20, 2019 7:13 am

I tried GeoGebra for android. Seems like it could be ideal, but the UI seems to have a mind of its own! Not sure if it's buggy, or user error. I guess I actually have to RTFM to find out which.

Edit: on further use it's definitly capable, but a few annoyances. Deleting a slider deletes all associated functions. Can't seem to rename or reorder functions. Can't get a url to a sheet for convenient sharing. Desmos is definitely nicer to use, shame it can't handle complex numbers.

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