[expr]/[lcd] for polar patterns hopeless problem?

Jul 28, 2009 at 12:21am

[expr]/[lcd] for polar patterns hopeless problem?

I’m trying to make a simple demo of how mic polar patterns work. Everything is fine and according plan, except I can’t get LCD to draw the negative lobe of the mic correctly. I’ve been through it, so whatever it is either I don’t know or I can’t see. It looks to me like the numbers from the equations are right, but somewhere in the LCD is the problem– It simply draws the negative lobe of the pattern correctly, but on the positive side of the graph.

Profuse thanks for any clues here.
(Sorry about the size, I tried to take out everything I could.)

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#44916
Jul 29, 2009 at 7:22am

Any ideas? Is the issue clear? I tried to cut it down as much as I could, and most of what’s in it I imagine is straightforward. Help me, help you, help me…

Thanks!
Brian

#161746
Jul 29, 2009 at 8:30am

Hi,

Don’t know much about cardioid equations, but I think the problem is that the [poltocar] does not deal with negative amplitudes the way you might expect. I made some changes to your patch and it looks like hyper-cardioid bi-directional are now drawn correctly.

Davis

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#161747
Jul 29, 2009 at 5:09pm

Wow, that is absolutely awesome! I never would have suspected it was in [cartopol]. The summed pattern works beautifully now.

But the way the gradient pattern is drawn still lacks a negative lobe. I tried just copying what you did to the LCD drawing for the gradient pattern, and it didn’t quite work. I also tried adding back in a kludge I had before, just multiplying the gradient amount * -1. and sending it out with the positive value, but it didn’t work so well either. How could I address that?

I’d love a resource to learn more about how you were able to fix the summing, if one is out there for a math neophyte like me. Or maybe this is just a quirk of the Max object?

Again, many thanks for any further help finishing this off…
Brian

#161748
Jul 29, 2009 at 7:22pm

I might be wrong, but I think you may have just been missing the LCDinvert patch you had in the earlier version… I was just playing with that yesterday

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#161749
Jul 30, 2009 at 6:39am

Sorry about the late response (damn, it was hot today).

I’ve been thinking about it, and I’m pretty sure there’s nothing wrong with [poltocar]. Here’s the sensitivity equation:

S = Pressure + Gradient * cos(theta).

Under certain Pressure/Gradient combos, S will be negative. But if you think about it, negative Sensitivity is not really what your interested in. You want absolute Sensitivity. So, if you plot (theta, abs(S)), you get the output you’re expecting. I think that’s why you see the two lobes of a hyper-cardioid plot as being opposite from eachother in magazines. Anyways, I made some changes to your patch to demonstrate. I hope my explanations were clear.

Davis

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#161750
Jul 30, 2009 at 4:51pm

this is interesting…

so, pardon my silliness… but you could than add a fffb~ that will compensate from one mic to the other (multislider -> multislider), find away to control the audio distance, take a few tests with a few different mics… and have a mic modeler?

Probably a little more complicated than than, but that would be a good start i think…

#161751
Aug 3, 2009 at 5:08am

Yup, this is *exactly* something I’d like to do for my students to be able to experiment with mic position. I had designs on using sensors on the actual mics, so they can move them and they’d respond to distance and position. It’d be a chunk of work and is not on the horizon in the near-future, but I’d love to make it possible.

Thanks so much guys!

-Brian

#161752
Aug 4, 2009 at 2:18am

would love to give you a hand with that… been looking into it myself with the idea of extending it to amp modeling. drop me a line off list if you would like to collaborate.

#161753

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