Forums > MaxMSP

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

July 28, 2009 | 12:21 am

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.)

– Pasted Max Patch, click to expand. –

July 29, 2009 | 7:22 am

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


July 29, 2009 | 8:30 am

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

– Pasted Max Patch, click to expand. –

July 29, 2009 | 5:09 pm

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


July 29, 2009 | 7:22 pm

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

– Pasted Max Patch, click to expand. –

July 30, 2009 | 6:39 am

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

– Pasted Max Patch, click to expand. –

July 30, 2009 | 4:51 pm

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…


August 3, 2009 | 5:08 am

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


August 4, 2009 | 2:18 am

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.


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