Gain Matching vs. Level Matching - AVS Forum
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post #1 of 94 Old 02-27-2013, 10:12 AM - Thread Starter
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Say you have 3 or 4 subs - 2 up front and 1 or 2 behind the MLP. The sub(s) behind the MLP are obviously much closer to the listener. When gain matching, wouldn't the output of the rear sub(s) overwhelm the front subs output? When using multiple subs, with widely varying positions, wouldn't it be better to level match?

I'm sure my thinking on this is wrong, just need someone smarter than me to explain it to me. biggrin.gif

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post #2 of 94 Old 02-27-2013, 10:49 AM
 
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Quote:
Originally Posted by Alan P View Post

I'm sure my thinking on this is wrong, just need someone smarter than me to explain it to me. biggrin.gif

Being the world's dumbest man and by international decree, also holding the award for the most incompetent man alive, you won't be getting one smarter than you but my understanding, one independently gain matches, at the main listening positions, using the gain control of each subwoofer, each subwoofer turned on, one at a time, running pink noise through the AVR, with the AVR's levels (internal gain control) set to zero.

Then, after running the EQ programs, dial things in with the levels (AVR internal gain control) to taste with all subs simultaneously turned on as now you're dealing with a single combined subwoofer output.

As to the position of the sub (distance) from the main listening position, that's a time domain/phase issue as you want the sound waves to arrive at the MLP, at the same time so you're not getting cancellation; nulls.

Good luck. biggrin.gif
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post #3 of 94 Old 02-27-2013, 10:55 AM - Thread Starter
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Yo BeeMan!

Not to beat a dead horse, but this:
Quote:
...one independently gain matches, at the main listening positions...,

is LEVEL matching. biggrin.gif

Some folks here extol the virtues of gain matching - placing each sub in a marked, neutral position (middle of room) with a stationary mic and adjusting each sub's gain (one at a time) to match each other. Now, I've done this, and I've gotten better response because of it...but, I'm able to localize my back subs more now than when I was using level matching. I'm just curious as to how gain matching and multiple subs (with some nearfield) is supposed to work.

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post #4 of 94 Old 02-27-2013, 11:01 AM
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Quote:
Originally Posted by BeeMan458 View Post

Quote:
Originally Posted by Alan P View Post

I'm sure my thinking on this is wrong, just need someone smarter than me to explain it to me. biggrin.gif

Being the world's dumbest man and by international decree, also holding the award for the most incompetent man alive, you won't be getting one smarter than you but my understanding, one independently gain matches, at the main listening positions, using the gain control of each subwoofer, each subwoofer turned on, one at a time, running pink noise through the AVR, with the AVR's levels (internal gain control) set to zero.

Then, after running the EQ programs, dial things in with the levels (AVR internal gain control) to taste with all subs simultaneously turned on as now you're dealing with a single combined subwoofer output.

As to the position of the sub (distance) from the main listening position, that's a time domain/phase issue as you want the sound waves to arrive at the MLP, at the same time so you're not getting cancellation; nulls.

Good luck. biggrin.gif

No arguement here and you never fail to disappoint.

In a nutshell. move one sub to the center of the room. Using a spl meter place it a few inches from the sub and take a measurement adjusting the subs gain to 80db (the number I use). Turn the sub off and move out of the way. Then move the next sub into the same spot as the previous sub and measure at the same distance and to the same db lvl.
Now you're gain matched.

Measuring subs at your main seat is level matching.
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post #5 of 94 Old 02-27-2013, 11:02 AM - Thread Starter
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Quote:
Originally Posted by sputter1 View Post

Measuring subs at your main seat is level matching.

Yes, yes...I know this - but, what about my quandary above??

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post #6 of 94 Old 02-27-2013, 11:02 AM
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Quote:
Originally Posted by Alan P View Post

When gain matching, wouldn't the output of the rear sub(s) overwhelm the front subs output?
Not really, because of the dominance of reflected versus direct radiation in what you're hearing. That makes the situation totally different than the other speakers, where what you primarily hear is direct radiation.

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post #7 of 94 Old 02-27-2013, 11:03 AM
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Well you guys beat me to it lol

No subwoofer I've heard has been able to produce the bass I've experienced in the Corps!

Must..stop...buying...every bluray release...
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post #8 of 94 Old 02-27-2013, 11:04 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Not really, because of the dominance of reflected versus direct radiation in what you're hearing. That makes the situation totally different than the other speakers, where what you primarily hear is direct radiation.

Not really?? So, it might be?

Thanks for joining in, Bill!

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post #9 of 94 Old 02-27-2013, 11:09 AM
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Quote:
Originally Posted by Alan P View Post

Quote:
Originally Posted by sputter1 View Post

Measuring subs at your main seat is level matching.

Yes, yes...I know this - but, what about my quandary above??

lol, my post was directed at the "Being the world's dumbest man and by international decree, also holding the award for the most incompetent man alive" guy
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post #10 of 94 Old 02-27-2013, 11:11 AM
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Quote:
Originally Posted by Alan P View Post

Not really?? So, it might be?
It depends on the room size. The smaller the room the less of an issue it will be. In a full size theater I'd worry about it, but not in a home theater.

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post #11 of 94 Old 02-27-2013, 11:16 AM - Thread Starter
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Hmmm...OK, Bill. But why do I feel I can now localize my rear subs better after gain matching? I s'pose it could just be in my head....

I've thought about turning down the crossovers on the rear subs (to say, 40hz) to help the localization - do you think this would be detrimental or beneficial? Should I gain match again at the new crossover point, or just leave the gain where it's at? I'm guessing just leave it....

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post #12 of 94 Old 02-27-2013, 11:18 AM
 
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Quote:
Originally Posted by Alan P View Post

Yo BeeMan!

Not to beat a dead horse, but this:
is LEVEL matching. biggrin.gif

Some folks here extol the virtues of gain matching - placing each sub in a marked, neutral position (middle of room) with a stationary mic and adjusting each sub's gain (one at a time) to match each other. Now, I've done this, and I've gotten better response because of it...but, I'm able to localize my back subs more now than when I was using level matching. I'm just curious as to how gain matching and multiple subs (with some nearfield) is supposed to work.

When I use the gain control to match levels, I'm gain matching the final levels. (I know you guys "THINK" I'm confused on this issue, but I'm not the confused one.)

I match at a measured 1m and then adjust at the MLP because of distant differences, the final SPL will be different as we both know, sound pressure levels fall off as the distance increases. The important point I wanted to share was to make sure the internal AVR gain control is set to zero during this gain matching and then run the EQ program.

Either which way, you had the privilege of the dumbest man in the world who holds international title to the most incompetent man in the world, trying to give you a helping hand. biggrin.gif
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post #13 of 94 Old 02-27-2013, 11:18 AM
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Quote:
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Not really, because of the dominance of reflected versus direct radiation in what you're hearing. That makes the situation totally different than the other speakers, where what you primarily hear is direct radiation.

Not really?? So, it might be?

Thanks for joining in, Bill!

I guess in a really large room near sub might reach you sooner than the farther sub if gain matched atleast on paper. Hard to say if you would tell by hearing.
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post #14 of 94 Old 02-27-2013, 11:24 AM - Thread Starter
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Originally Posted by sputter1 View Post

I guess in a really large room near sub might reach you sooner than the farther sub if gain matched atleast on paper. Hard to say if you would tell by hearing.

I'm not saying the near sub would reach you sooner, I'm saying that the SPL of the near sub(s) is higher than the far sub(s) at the MLP when gain matched. How do you compensate for this when gain matching? Or, does it need to be compensated for at all??

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post #15 of 94 Old 02-27-2013, 11:25 AM - Thread Starter
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Quote:
Originally Posted by BeeMan458 View Post

When I use the gain control to match levels, I'm gain matching the final levels. (I know you guys "THINK" I'm confused on this issue, but I'm not the confused one.)

I match at a measured 1m and then adjust at the MLP because of distant differences, the final SPL will be different as we both know, sound pressure levels fall off as the distance increases. The important point I wanted to share was to make sure the internal AVR gain control is set to zero during this gain matching and then run the EQ program.

Either which way, you had the privilege of the dumbest man in the world who holds international title to the most incompetent man in the world, trying to give you a helping hand. biggrin.gif

Yes, BeeMan - we're all very familiar with your "gain matching" procedure. smile.gif

However, I'm referring to the more widely accepted AVS definition of gain matching. wink.gif

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post #16 of 94 Old 02-27-2013, 11:27 AM
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Quote:
Originally Posted by Alan P View Post

I'm not saying the near sub would reach you sooner, I'm saying that the SPL of the near sub(s) is higher than the far sub(s) at the MLP when gain matched. How do you compensate for this when gain matching? Or, does it need to be compensated for at all??
It doesn't need to be compensated for with respect to the rear sounding louder. It may need to be compensated for in terms of achieving maximum smoothing of response at the LP. The only way to know that is by monitoring the room response while adjusting the volumes, to see the result on the RTA chart.

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post #17 of 94 Old 02-27-2013, 11:28 AM
 
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Quote:
Originally Posted by Alan P View Post

I'm not saying the near sub would reach you sooner, I'm saying that the SPL of the near sub(s) is higher than the far sub(s) at the MLP when gain matched. How do you compensate for this when gain matching? Or, does it need to be compensated for at all??

What does Newton have to say on the matter when one has unequal forces meeting each other. If it doesn't matter, then it doesn't matter where one is located when they measure the gain control set output of their subs.
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post #18 of 94 Old 02-27-2013, 11:29 AM
 
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Originally Posted by Alan P View Post

Yes, BeeMan - we're all very familiar with your "gain matching" procedure. smile.gif

However, I'm referring to the more widely accepted AVS definition of gain matching. wink.gif

If that's what you're doing, you already know the answer to your question.
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post #19 of 94 Old 02-27-2013, 11:30 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It doesn't need to be compensated for with respect to the rear sounding louder. It may need to be compensated for in terms of achieving maximum smoothing of response at the LP. The only way to know that is by monitoring the room response while adjusting the volumes, to see the result on the RTA chart.

Awesome! That's just what I'll do then.

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What does Newton have to say on the matter when one has unequal forces meeting each other. If it doesn't matter, then it doesn't matter where one is located when they measure the gain control set output of their subs.

Let's please not start this debate up again in my thread. rolleyes.gif

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post #20 of 94 Old 02-27-2013, 11:32 AM
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Quote:
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Quote:
Originally Posted by sputter1 View Post

I guess in a really large room near sub might reach you sooner than the farther sub if gain matched atleast on paper. Hard to say if you would tell by hearing.

I'm not saying the near sub would reach you sooner, I'm saying that the SPL of the near sub(s) is higher than the far sub(s) at the MLP when gain matched. How do you compensate for this when gain matching? Or, does it need to be compensated for at all??

I got you, I don't. My only concern is that the AVR sub trim is close to 0db which may mean I have to redo the gain matching process either up or down dependant on with the sub trim shows.
Is that what you want to know?
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post #21 of 94 Old 02-27-2013, 11:34 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It doesn't need to be compensated for with respect to the rear sounding louder. It may need to be compensated for in terms of achieving maximum smoothing of response at the LP. The only way to know that is by monitoring the room response while adjusting the volumes, to see the result on the RTA chart.

Thanks again, BIll. I did the whole RTA thing with phase, but didn't think to do it with the sub volumes. Here's to an even smoother response!! biggrin.gif

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post #22 of 94 Old 02-27-2013, 11:39 AM
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Quote:
Originally Posted by Alan P View Post

Hmmm...OK, Bill. But why do I feel I can now localize my rear subs better after gain matching? I s'pose it could just be in my head....

I've thought about turning down the crossovers on the rear subs (to say, 40hz) to help the localization - do you think this would be detrimental or beneficial? Should I gain match again at the new crossover point, or just leave the gain where it's at? I'm guessing just leave it....

I think it's in your head (i'm not trying to be smartass). I can place one sub behind my couch and run it only and not be able to point it out. It wasn't what I was expecting the first time I tried it, I fully expected to tell.
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post #23 of 94 Old 02-27-2013, 01:46 PM
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I think it's in your head (i'm not trying to be smartass). I can place one sub behind my couch and run it only and not be able to point it out. It wasn't what I was expecting the first time I tried it, I fully expected to tell.
+1. If you can locate it you've got directional frequencies in there that shouldn't be.

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post #24 of 94 Old 02-27-2013, 01:59 PM
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Hi Alan,

Can you try to describe the "localization" you're hearing? Localization is usually caused by hearing frequencies above about 80 to 100. It is manifested as hearing sounds "attached to" or "emanating from" the subwoofer. Often it's deep male voices where the fundamental frequency of the voice falls into that range. Darth Vader's voice comes to mind. If you are hearing his kind of directionality of specific sounds, that can usually be corrected with a lowering of the crossover. What crossover are you currently using? Also, what subs are you using? (Sorry, I forget.)

Another thing you can try is changing the closer subs' Distance setting. If your version of Audyssey has SubEQ2, you can set different Distances for one sub output than the other. The "Precedence Effect" states that directionality is determined by the first arriving sound, even if the later arriving sound is louder. Therefore, try adding a foot or 2 to the rear subs, effectively delaying them 10 or 20 ms. The front subs will arrive first and define the directionality and the rear subs will arrive later and add volume. However, be careful as these types of changes can also impact the FR. (Disclaimer: The Precedence Effect, or Haas Effect is usually defined with midrange frequencies. I'm not sure how low in frequency it applies, so don't take this as gospel.)

OTOH, if you a just "sensing" that all the bass is coming from behind, that is a different issue and it won't be corrected with a crossover change. Lowering the levels of the rear subs might help, but remember that you can run into issues with headroom if you use different trim settings or gain settings for one or more of the subs. Nonetheless, that may be a worthwhile tradeoff if it works.

I have 3 subs placed around my room at different distances to the LP, and I'm using a 100 Hz crossover on all my speakers. They're all 3 gain-matched, (using the AVS common definition of gain-matching.) I don't hear any one of my subs more prominently than any other sub. They all blend together and provide just one big bass response.

Craig
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post #25 of 94 Old 02-27-2013, 02:24 PM
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I'm wondering if it just isn't something nearby that's bringing attention to the sub. Say a sympathic vibration in the seat + the knowledge of where the sub is.
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post #26 of 94 Old 02-27-2013, 02:26 PM - Thread Starter
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Originally Posted by craig john View Post

Hi Alan,

Can you try to describe the "localization" you're hearing?

You got it spot on right here:
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OTOH, if you a just "sensing" that all the bass is coming from behind, that is a different issue and it won't be corrected with a crossover change.

It really doesn't bug me that much, I mostly just wanted to know why gain matching doesn't cause more localization issues - in my mind it should since the SPL of the closer subs will be higher at the MLP than the further subs - which Bill explained with the whole direct vs. reflected sound thing.

Like you said, I just get a sense that there is more bass coming from the back of the room than from the front, but it still sounds really, really good. biggrin.gif
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What crossover are you currently using? Also, what subs are you using?

Currently at 80hz, 2 PSA XS15s (up front) 1 Velodyne F1500 (back, soon to be replaced by 1, maybe 2 PSA XS15s cool.gif )
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Another thing you can try is changing the closer subs' Distance setting.

No dice, m AVR doesn't do multiple subs.

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post #27 of 94 Old 02-27-2013, 02:33 PM
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Localization frequencies are irrelevant in the subwoofer bandwidth. Run the sub hot and you'll "localize" it. Turn it up significantly higher than the mains and you'll pick it out of the crowd (of other speakers in the room) every time.

Here's one sub at 1M and an identical sub at 4M, gain matched. The inverse square law predicts a 12dB difference when doubling the distance twice (-6dB per doubling of distance), which is what the measurement confirms:



Anyone who can't hear one sub vs the other when there's a 12dB difference at his ears is too deaf to be posting in this thread. From 7 Hz down, it doesn't matter where you sit in this particular room (3500 cubes), but everywhere else across the BW... it matters.

Aside from the obvious crap shoot with the gross mismatch in arrival time (phase issues), calibrating the subs at the same neutral and irrelevant placement, then afterward placing them near field and far field simultaneously makes zero sense. If, as the OP has stated he has, you get a better FR at the LP with near field plus far field placement, then most certainly level match them at the LP.
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post #28 of 94 Old 02-27-2013, 02:40 PM
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I'm still a bit confused on the whole level vs gain matching thing. I have Audyssey XT32 and I've read posts from Chris of Audyssey that says it isn't necessary to gain match with XT32 and it also isn't necessary to get the subs volume as close to Odb as possible as long as they aren't maxed out.

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post #29 of 94 Old 02-27-2013, 02:42 PM
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Quote:
Originally Posted by Alan P View Post

You got it spot on right here:
It really doesn't bug me that much, I mostly just wanted to know why gain matching doesn't cause more localization issues - in my mind it should since the SPL of the closer subs will be higher at the MLP than the further subs - which Bill explained with the whole direct vs. reflected sound thing.

Like you said, I just get a sense that there is more bass coming from the back of the room than from the front, but it still sounds really, really good. biggrin.gif
Currently at 80hz, 2 PSA XS15s (up front) 1 Velodyne F1500 (back, soon to be replaced by 1, maybe 2 PSA XS15s cool.gif )
No dice, m AVR doesn't do multiple subs.
I would expect the problem to be completely corrected when you get your new sub(s). It is difficult to use gain-matching properly with different subs. The technique works best when all the subs are identical.

Craig

Lombardi said it:
Perfection is not attainable, but if we chase perfection we can catch excellence."


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post #30 of 94 Old 02-27-2013, 02:52 PM - Thread Starter
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Quote:
Originally Posted by bossobass View Post

Anyone who can't hear one sub vs the other when there's a 12dB difference at his ears is too deaf to be posting in this thread. From 7 Hz down, it doesn't matter where you sit in this particular room (3500 cubes), but everywhere else across the BW... it matters.

See, now...this is exactly what I was thinking!
Quote:
Aside from the obvious crap shoot with the gross mismatch in arrival time (phase issues), calibrating the subs at the same neutral and irrelevant placement, then afterward placing them near field and far field simultaneously makes zero sense. If, as the OP has stated he has, you get a better FR at the LP with near field plus far field placement, then most certainly level match them at the LP.

Just so I'm clear, Bosso - you advise against gain matching and against multiple subs being split between far and near field? I ask because there is no way I can fit all 4 subs in the front of my room....at least one will simply have to go in the back. I'm guessing if I have the ability to set phase on all of them (but not separate distances) I'll still be OK?

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