Optimizing subwoofers and integration with mains: multi sub optimizer - Page 2 - AVS Forum | Home Theater Discussions And Reviews
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post #31 of 797 Old 09-27-2015, 07:13 PM
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Originally Posted by andyc56 View Post
I've uploaded a new version today. It can be downloaded here. It adds support for miniDSP-compatible biquad text format in the filter reports, so you can copy and paste this information into the miniDSP software directly without having to enter individual filter parameters manually.
That's awesome!
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post #32 of 797 Old 09-27-2015, 08:05 PM
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Thanks!
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Originally Posted by Gooddoc View Post
That's awesome!
Thanks for the kind words guys. Here's a bit more info. If the given filter channel has less than 6 biquads, the software fills in the missing remainder with "through connection" biquad elements with b0 = 1 and the rest of the coefficients = 0. If the filter channel has more than 6 biquads, it will show the coefficients of all of them, but the result won't be compatible with the miniDSP PEQ biquads and a warning is displayed. One can, I think, load up to 8 biquads in the crossover section of a miniDSP for a grand total of 14 biquads per channel. I'll need to check their documentation again to refresh my memory on the details of this, as I don't have a miniDSP myself.

One thing I thought about but did not implement is to modify the filter report so that it shows which biquads implement which filters (something like FL7: biquad3, biquad4). I was careful to arrange the more complex filters like high-order Butterworth so that the biquads are ordered by increasing Q of the second-order factors in the corresponding analog filter. This is because e.g. Butterworth filters are a combination of second-order factors with considerable "droop" combined with others having peakiing. You want the biquads having frequency response droop to be before the ones with peaking to prevent internal digital overload.

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post #33 of 797 Old 09-28-2015, 03:47 PM
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Is there any way to use this without having main channels defined? I just wanted to see what it came up with for combining the subs alone without worrying about the mains for now.
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post #34 of 797 Old 09-28-2015, 05:09 PM
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Is there any way to use this without having main channels defined? I just wanted to see what it came up with for combining the subs alone without worrying about the mains for now.
Main channels need to be defined. I wrote more about that here.
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post #35 of 797 Old 10-03-2015, 11:28 PM
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There's a new version of MSO up. Download link is here. It adds the capability of saving graphs as PNG files without having to use a third-party screen capture program. Also, filter biquad reports have been modified so that filters are associated with biquads as follows:

Sub Channel 1:
FL3: LPF Linkwitz-Riley 24 dB/oct (biquad1, biquad2)
FL4: Parametric EQ (biquad3)
FL5: Parametric EQ (biquad4)
FL6: Parametric EQ (biquad5)
FL7: Parametric EQ (biquad6)
biquad1,
b0=0.000061216865655,
b1=0.000122433731309,
b2=0.000061216865655,
a1=1.977747949570286,
a2=-0.977992817032904,biquad2,
[...etc...]

In addition, new graphs default to manual mode 20 Hz - 200 Hz for x-axis limits.

I'd like to change directions a bit and provide a tutorial with detailed procedures, screen shots and so on. So that's my focus for now.

I'd also be interested in inputs from users who wish to use MSO to optimize just their subs without measuring main speakers. Currently this isn't possible, but I have some ideas of how to implement this. I'd especially be interested in hearing from those using Dirac for system EQ.

Last edited by andyc56; 10-03-2015 at 11:55 PM.
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post #36 of 797 Old 10-07-2015, 12:26 PM
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I've been writing up a tutorial that walks you through all the steps needed to create a project and gain a good understanding of the software and its user interface. The current documentation is too general in nature and has no screen shots, as I was trying to get something out quickly when I originally wrote it up. It will take at least another week to finish up the tutorial, which to start with will be in PDF form only.

However, when writing it up, I found a bug in the software causing an error message to be generated when you try to import more than about 15 FRD files at one time. There's no crash or instability, but not all the files will import and it requires importing the missing ones on a second pass.

I've uploaded a new version that fixes this problem. I highly recommend that older versions not be used. You can download the new version here.
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post #37 of 797 Old 10-07-2015, 12:50 PM
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Originally Posted by andyc56 View Post
I've been writing up a tutorial that walks you through all the steps needed to create a project and gain a good understanding of the software and its user interface. The current documentation is too general in nature and has no screen shots, as I was trying to get something out quickly when I originally wrote it up. It will take at least another week to finish up the tutorial, which to start with will be in PDF form only.

However, when writing it up, I found a bug in the software causing an error message to be generated when you try to import more than about 15 FRD files at one time. There's no crash or instability, but not all the files will import and it requires importing the missing ones on a second pass.

I've uploaded a new version that fixes this problem. I highly recommend that older versions not be used. You can download the new version here.
Do you have sample files to play with by any chance? I'd like to try this out, but lack a mic with loopback timing.

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post #38 of 797 Old 10-07-2015, 01:04 PM
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Originally Posted by andyc56 View Post

I'd also be interested in inputs from users who wish to use MSO to optimize just their subs without measuring main speakers. Currently this isn't possible, but I have some ideas of how to implement this.
What is the challenge in not having a main channel? Algorithmically I mean.

My thought was to use something like a 2-300Hz Butterworth high pass as the source of an frd for the mains btw. Would this be a feasible way to trick it into playing nicely?
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post #39 of 797 Old 10-07-2015, 01:09 PM
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Do you have sample files to play with by any chance? I'd like to try this out, but lack a mic with loopback timing.
I've just uploaded some sample files (courtesy of Jag768). You can get them here.

Edit: I've replaced the sample files I linked to earlier with the samples from the new tutorial. The tutorial itself in zipped PDF format can be found here.

Edit 2: The PDF tutorial is now obsolete and I won't be updating it. The latest tutorial is online in HTML format, or you can download the .CHM help file, which contains the same information.

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post #40 of 797 Old 10-07-2015, 03:22 PM
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What is the challenge in not having a main channel? Algorithmically I mean.
When I originally went about designing it, I didn't realize how much interest there would be in optimizing just the subs by themselves. The software was conceived as a kind of integration technology, which has been conspicuously missing from the scene so far.

When multiple listening positions are considered, the integration of mains and subs is more complex than it might appear. Broad humps or dips may appear in the combined responses in the frequency region where it should be flat, and these are, for the purposes of the algorithm, much like shifts in reference level, because they shift the mean of the response over frequency as a function of listening position (and also as a function of filter parameters on each pass). The solution of this problem is to calculate the mean on each pass of the optimizer (millions of times IOW) over a frequency range for which the response is nominally flat without EQ (the reference frequency range), and separately for each listening position. This in turn requires that the mean (the reference level) not be specified as fixed.

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My thought was to use something like a 2-300Hz Butterworth high pass as the source of an frd for the mains btw. Would this be a feasible way to trick it into playing nicely?
It's an interesting idea, but if the listening positions have significantly different relative distances from the subs, the SW would be trying to integrate them with a fake mains response whose delay didn't vary with listening position as the mains surely would. That would likely give erroneous results.

When I was thinking about this, the only solution I could come up with was to add a high-shelf filter to the software and first use it to flatten out the inductance hump of the subs using a near-field measurement. The inductance hump alone makes the choice of reference level rather nebulous, as there may be no flat region at all. Currently, gain blocks are allowed on all subs, but this wouldn't work if there were no mains, as the absolute level would just shift up and down arbitrarily (because the SW only cares about flatness). The software would have to be changed so that, if no mains are present, having gain blocks (and delay blocks) on all subs would be disallowed, and only allow them on N-1 subs, where N is the number of independently-controlled subs.
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post #41 of 797 Old 10-08-2015, 01:48 AM
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Sounds like a plan But I would probably create a second app just for sub optimization and have MSO do what it is intended for. Trying to make MSO please everybody will probably end up in a support/bug monster.

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post #42 of 797 Old 10-15-2015, 04:00 PM
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I just put a new version up again. It can be downloaded here. While working on the tutorial, I found some usability issues and minor bugs that I've put in fixes for. These are the changes:
  • Changed the maximum allowable Q for PEQ filters from 16 (as recommended by Welti and Devantier) to 30. The default maximum is 25, and I don't recommend going higher than that, as it can lead to "spiky" frequency responses. But there are improvements to be had going from 16 to 25.
  • For large projects, too many nodes in the tree views were being expanded when the project was loaded from disk. I tried to only expand the nodes that are most often used (e.g the ones that represent the filters and allow you to modify them). Also, tree views scroll to the top after reading in a project.
  • Pressing Cancel in the Add Measurement Group dialog caused an empty group to be created instead of canceling out of the operation altogether. Now fixed.

The tutorial is coming along, but it's taking a bit longer than I expected, as I've been interrupting doing it with minor bug fixes.
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post #43 of 797 Old 10-15-2015, 10:10 PM
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You're welcome! I was inspired by the Geddes video about multiple subwoofers.
Hahaha. I'm the guy in black in the middle of the picture there. I had read up on his methods, with plans to implement, and after that meeting I understood enough to conceptualize the software (as an aid to completing the manual method he's described much more quickly) a few days later.
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post #44 of 797 Old 10-15-2015, 10:29 PM
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Hahaha. I'm the guy in black in the middle of the picture there. I had read up on his methods, with plans to implement, and after that meeting I understood enough to conceptualize the software (as an aid to completing the manual method he's described much more quickly) a few days later.
Great minds think alike! It was an inspiring presentation.
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post #45 of 797 Old 10-16-2015, 07:57 AM
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Great minds think alike! It was an inspiring presentation.
I re-watched it last night. I hadn't caught before that he was working in MathCad. I wonder if that made the job particularly easy.

It was interesting to hear him say he used to have delay in his software but never needed it. My starting point was probably going to be to time-align each sub to the mains using the impulse response from a +/-5Hz sweep through the crossover range measured at the MLP a la this thread: http://www.hometheatershack.com/foru...ng-rew-v5.html ...and then go from there.

Also it was interesting to hear that he didn't think you needed a sub up high. He's stated in the past that the rear sub should be up high and since I have a closet in the back I was going to put a sub up on a shelf there. It stands to reason that might give some degree of vertical modal control/smoothing, but the fact that he states here it's unimportant has me wondering if I'd be better off building a more powerful sub and putting it on the floor in there rather than dealing with building it small enough, reinforcing the shelf, and trying to make sure it can't slide off.
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post #46 of 797 Old 10-16-2015, 09:28 AM
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I re-watched it last night. I hadn't caught before that he was working in MathCad. I wonder if that made the job particularly easy.
I didn't catch that either, and I've seen it multiple times. Regarding MathCad, the last I checked, which was years ago, it was using the Levenberg-Marquardt method for optimization. My previous experience with optimization was in connection with SPICE transistor model extraction. All the optimizers I tried (including Levenberg-Marquardt) had a bad tendency to converge on local minima of the objective function (cost function). With SPICE model extraction, that problem becomes clear because the simulated vs. measured curves don't match up. The best algorithm I found was differential evolution (DE), though it was by far the slowest. It also requires the user to tune the optimizer to the problem, which is a no-no. I found a self-tuning variant of DE called JADE, which I coded up and used based on the description in this paper (right-click the document icon to save). It is slow though. Using a problem having 60 adjustable parameters such as Jag768's project, I've found that after running it for 20 minutes, it finds a significantly better solution than what it found after 10 minutes.

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It was interesting to hear him say he used to have delay in his software but never needed it. My starting point was probably going to be to time-align each sub to the mains using the impulse response from a +/-5Hz sweep through the crossover range measured at the MLP a la this thread: http://www.hometheatershack.com/foru...ng-rew-v5.html ...and then go from there.
Not using delays doesn't seem right to me, though I've noticed that if you limit the delays to small values in MSO, it seems to work around that.

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Also it was interesting to hear that he didn't think you needed a sub up high. He's stated in the past that the rear sub should be up high and since I have a closet in the back I was going to put a sub up on a shelf there. It stands to reason that might give some degree of vertical modal control/smoothing, but the fact that he states here it's unimportant has me wondering if I'd be better off building a more powerful sub and putting it on the floor in there rather than dealing with building it small enough, reinforcing the shelf, and trying to make sure it can't slide off.
I hadn't thought about that much, as a sub up high isn't in the cards for me. Having subs with different capabilities makes the optimization problem harder though. If the optimizer determines that a given DSP channel should be 10 dB lower in level than the others, and the other electronics in the system are otherwise the same, what if that happens to be the channel assigned to the most powerful sub? That will require extra work.

Last edited by andyc56; 10-16-2015 at 09:49 AM.
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post #47 of 797 Old 10-16-2015, 12:17 PM
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I switched to using Matlab's more extensive optimization routines although Mathcad has some addons that are pretty good. I found Mathcad support tapered off after PTC bought them, and the upgrade price skyrocketed so I haven't upgraded my old Mathcad (v14). Matlab did the same thing years ago (took my upgrade from $300 to $1300 one year) but I recently noticed they offer a "home" version so I picked one up a few weeks ago. Now to take all my Mathcad files, converted from Matlab, back into Matlab again...

I think the Matlab optimization package (toolbox) has JADE but am not sure. Didn't buy that toolbox (so far).

I may just stick it all in Python.

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post #48 of 797 Old 10-16-2015, 12:25 PM
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I think the Matlab optimization package (toolbox) has JADE but am not sure. Didn't buy that toolbox (so far).
There's a pretty good free Matlab differential evolution package (but not JADE) by Markus Buehren here.
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post #49 of 797 Old 10-16-2015, 06:06 PM
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Cool, thank you sir!

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post #50 of 797 Old 10-16-2015, 10:49 PM
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Regarding MathCad, the last I checked, which was years ago, it was using the Levenberg-Marquardt method for optimization.
OK, wow. I know just enough to be dangerous but since I haven't done EE or softie stuff professionally this discussion went way beyond me. LOL, and here I was mostly concerned with just getting the manual / no-auto-optimization version working.

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Having subs with different capabilities makes the optimization problem harder though
We'll see if things get interesting. I'm initially planning 2x two-driver subs in front of room, 1x two-driver sub in the riser under the couch at MLP, and 1x one-driver sub inside the rear closet on the shelf. However all of them will be nominal 4ohm and similar amplifier powers so a 3-6dB less capability for the rear one. The two subs in the front of the room can have another of the same unit stacked on them if I'm not satisfied with the amount of output. However even if I do wind up using the second set of front units, I don't think it'll change much from an EQ perspective because my goal is flat-to-10Hz at close to reference so the limiting factor in my output will be below the modal region anyway.

Arg, need to start a build thread.
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post #51 of 797 Old 10-21-2015, 02:46 PM
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I finally have a tutorial up now. It consists of two parts: a zipped PDF file and a zipped file of sample data and projects. There's plenty of screen shots and the tutorial walks you through the creation of a project step by step.

The tutorial hasn't been folded into the CHM help files yet, as I have yet to convert it to HTML.
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post #52 of 797 Old 10-24-2015, 04:23 PM
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I've made a few corrections to the MSO tutorial PDF (download zip file here). I've also converted it to HTML and folded that into the CHM help file as well as putting it up on the MSO web pages.

Next up is to make an installer program, and for that I have to figure out the NSIS installer creator.

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post #53 of 797 Old 10-25-2015, 12:08 PM
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There is an installer now. The new version of mso.zip (download here) contains only install_mso.exe, which is the new installer. This should get rid of the problem with the CHM file showing up as blank and needing to "unblock" it.

I thought I'd just give a quick overview of the example in the tutorial. It uses data provided by Jag768, in which he uses a Geddes-style configuration. This configuration is as follows:
  • No high-pass on the mains
  • An LR4 low-pass for each sub, but with different cutoff frequencies allowed for each one
  • Separate delay for each sub
  • Separate gain for each sub
  • Four PEQ filters per sub

Once the project is set up and configured to display the combined response of main speakers and all subs at each listening position, you get the following result before optimization. The plots use offsets to separate the traces. The top trace has no offset, while the next three have offsets of -15 dB, -30 dB and -45 dB respectively.



This room is problematic, with lots of peaks and dips in the responses, especially at listening position 3. Then the optimization is run, and the following result is obtained.



There's good improvements, not only in the response at the MLP, but also with seat-to-seat variation. The responses of the sub channels, which have the PEQs constrained to only cut, not boost, are shown below.



Strange looking responses! If your goal is to maximize output, the gains would have to be constrained to not vary as much, but this would probably result in worse flatness of the responses after optimization.

The response at the MLP could be further flattened using the shared filters on the subs if desired.
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post #54 of 797 Old 10-27-2015, 02:09 PM - Thread Starter
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The tutorial looks good, as well as the help file .

I changed my setup to a more Floyd-style-like placement, having one sub on each side of the main listening positions/couch and the others on the opposite wall. This reduces the influence of the first mode. I also made a target curve which is a somewhat downsloping curve (about 6dB down at 100Hz compared to 20Hz). Otherwise it sounded to thin to me .

I can recommend everybody who has interest in multi sub setups, to read the tutorial and help file on the website of andy.
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post #55 of 797 Old 10-28-2015, 06:04 AM
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I also made a target curve which is a somewhat downsloping curve (about 6dB down at 100Hz compared to 20Hz). Otherwise it sounded to thin to me .
I need to add a section to the tutorial about target curves. But before doing that, there needs to be some kind of target curve editor. I'm still scratching my head about the best way to do it.
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post #56 of 797 Old 10-31-2015, 03:17 PM
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I finally have a tutorial up now. It consists of two parts: a zipped PDF file
If you're interested in the link to the Geddes video, skip to 1:27:00 in the ustream broadcast to get to the beginning of his presentation.
And the ads are annoying.

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post #57 of 797 Old 10-31-2015, 06:11 PM
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If you're interested in the link to the Geddes video, skip to 1:27:00 in the ustream broadcast to get to the beginning of his presentation.
And the ads are annoying.

Michael
I just use this link to go directly to the Geddes presentation in the video and this link for the PowerPoint presentation. I didn't realize there were any ads with the video at all, as I'm using Firefox with the AdBlock Plus plugin. I believe you can get AdBlock Plus for Chrome as well.
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post #58 of 797 Old 11-01-2015, 12:43 PM
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I thought I'd just give a quick overview of the example in the tutorial. It uses data provided by Jag768, in which he uses a Geddes-style configuration. [...] the following result is obtained. [...]
Pretty good results! How far are the positions apart?

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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post #59 of 797 Old 11-01-2015, 02:07 PM
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Pretty good results! How far are the positions apart?
I don't know the exact distances, but the configuration is in post 3 of this thread.

I was thinking that if users wanted to further flatten the MLP, they could use shared EQ on the subs. Then the per-sub filter parameters could be locked and only the shared filters adjusted, optimizing only the MLP response flatness. But then I realized there's an undesired dependency. If you want to plot a measurement group, it needs to be defined under "Measurement groups to optimize". But then that group will be optimized too. For the case of "final cleanup of the MLP", you'd want to optimize only the MLP with the shared filters (since the per-sub optimization has already been done), yet plot all positions. So there needs to be a way to disable optimization on some groups that are defined, so that they can be plotted but not optimized. I'm going to add that, as it's definitely an oversight on my part.
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post #60 of 797 Old 11-02-2015, 02:10 AM
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I don't know the exact distances, but the configuration is in post 3 of this thread.
Pretty far apart. Ultimative test would be to have control points at other locations and check if they benefit from the optimization too.

Markus

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