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Equalizer APO, REW and Rephase WOW!
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Old 10th March 2018, 10:40 AM   #81
TNT is offline TNT  Sweden
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Originally Posted by HammerSandwich View Post
How are you correcting phase to make this kind of crossover sum correctly?
Isnt he whole idea that they don't sum. If they don't overlap, they don't need to sum. -90 dB 5 Hz away.

Well there is a 6 Hz wide passband that will be wacky... is that a problem?

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Last edited by TNT; 10th March 2018 at 10:43 AM.
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Old 10th March 2018, 03:22 PM   #82
HammerSandwich is offline HammerSandwich
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Originally Posted by jiiteepee View Post
He means that GraphicEQ outputs IR data for internal convolution engine so, that's why you can make filters with nearly arbitrary frequency response without screwing the phase.
Jonas opens this a bit here
Thank you for finding this. It clearly states that EQAPO's GraphicEQ is minimum-phase, meaning that you canNOT use it to make filters as you state. (Convolution can process amplitude & phase independently, but not every convolution operation actually does.) These filters won't screw phase for FR correction, but they clearly won't create a linear-phase crossover without additional correction via another method.

Really, that distinction is the major focus of this thread. Note "rePhase" in the title.

And this point contradicts what 33Polk posted earlier:
Quote:
Originally Posted by 33Polkhigh View Post
There is no analog phase shift, so no need to. It's getting rid of the phase issues that would be in a typical crossover.
That's all I've been trying to point out.

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Originally Posted by 33Polkhigh View Post
Let's just assume that there was no such thing as phase shift.

The real issue is that if you are crossing over to a tweeter that is at a different spot on the baffle...
I understand these things & am trying to highlight a different aspect of your method. Or, at least, what I believe your method is. But you're moving the goalposts, rather than addressing my concerns. When someone brings up phase issues, we won't get very far by immediately assuming it doesn't exist...

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Originally Posted by msibilia View Post
I was concerned about the same thing, but I have measured the before and after amplitude and phase response, and I get what I am expecting, so it is possible.
Marc, I agree that the method you describe can work. However, I believe that 33Polk is not using rePhase at all. I certainly can't find any evidence of it.

If I'm correct, his method of using incredibly steep, minimum-phase filters for his crossovers has consequences. And it's certainly not as simple as "there's no reason to not go very steep." For example, the Grimm paper I mentioned before has some interesting comments about the off-axis behavior of steep XOs.

Quote:
Originally Posted by TNT View Post
Isnt he whole idea that they don't sum. If they don't overlap, they don't need to sum. -90 dB 5 Hz away.

Well there is a 6 Hz wide passband that will be wacky... is that a problem?
Well said, indeed. Unlike what I posted! I'll stick to the minimum- versus linear-phase detail for now.
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Old 11th March 2018, 06:02 AM   #83
33Polkhigh is offline 33Polkhigh  United States
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Quote:
Originally Posted by HammerSandwich View Post
These filters won't screw phase for FR correction, but they clearly won't create a linear-phase crossover without additional correction via another method.

Really, that distinction is the major focus of this thread. Note "rePhase" in the title.

And this point contradicts what 33Polk posted earlier:That's all I've been trying to point out.


I understand these things & am trying to highlight a different aspect of your method. Or, at least, what I believe your method is. But you're moving the goalposts, rather than addressing my concerns. When someone brings up phase issues, we won't get very far by immediately assuming it doesn't exist...

If I'm correct, his method of using incredibly steep, minimum-phase filters for his crossovers has consequences. And it's certainly not as simple as "there's no reason to not go very steep." For example, the Grimm paper I mentioned before has some interesting comments about the off-axis behavior of steep XOs.
I will look at the Grimm paper at some point.

However I never said or assumed that phase shift "doesn't exist". The point is simply that when you have sound coming from two sources more than 1/4 wavelength apart they will be interfering with each other, at certain points in space, period.

So you can't eliminate physical phase issues with rephase or "linear phase" crossovers of anything else.

Thus a very steep slope that transitions from one driver to another over a few hz is desirable and will be less audible.

I'm not an expert on the electrical phase of AC circuits, but I highly doubt that whatever algorithm being used in Equalizer APO is introducing the same kind of electrical phase shifts that are present in a typical crossover. If it is, fine, all the more reason to use a steep slope and rapid transition between drivers, since the issues are of a physical nature.

If you accept that it is preserving phase as a equalizer then it will doing the same as a crossover.
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Old 11th March 2018, 07:29 AM   #84
jiiteepee is offline jiiteepee  Finland
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Quote:
Originally Posted by 33Polkhigh View Post
...

Thus a very steep slope that transitions from one driver to another over a few hz is desirable and will be less audible.

I'm not an expert on the electrical phase of AC circuits, but I highly doubt that whatever algorithm being used in Equalizer APO is introducing the same kind of electrical phase shifts that are present in a typical crossover. If it is, fine, all the more reason to use a steep slope and rapid transition between drivers, since the issues are of a physical nature.

If you accept that it is preserving phase as a equalizer then it will doing the same as a crossover.
Splitting bands with Linkwitz-Riley.
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Old 18th March 2018, 10:08 PM   #85
33Polkhigh is offline 33Polkhigh  United States
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After some more research here's what I found;

1. Equalizer APO is apparently a linear phase equalizer. It has ZERO phase shift, not an issue whatsoever.

2. There are two issues with linear phase equalizers, one is delay which unless your a competitive gamer doesn't matter.

3. The other issue is ringing. This is more like an artifact from digital processing. How audible it is is debatable, but here a few articles addressing it.

Linear Phase EQ Explained - Crave DSP

Pre and Post Effin Ringing and **** like that | Super Best Audio Friends

The bottom line is that steep slopes do sound better, but don't make them unnecessarily STEEP, because it can be an issue. I changed my crossover to between 950-1050 hz, so not crazy steep, but steep than a typical crossover.

The issue of ringing is IMO less of an issue than lobing or the phase shift of normal crossovers, but it exists nonetheless.

Last edited by 33Polkhigh; 18th March 2018 at 10:19 PM.
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Old 19th March 2018, 04:23 AM   #86
33Polkhigh is offline 33Polkhigh  United States
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Note that I still don't know for sure that it is a linear phase equalizer. If its minimum phase then its more like a mini-dsp, and maybe better in some respects. I should've asked some questions at the support page a long time ago.
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Old 19th March 2018, 07:40 AM   #87
KaffiMann is offline KaffiMann  Norway
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I had ringing on a sub once, it was really bad. Using 16th order filters and higher.
Worst was Elliptic. Butterworth and also Bessel worked reasonably well. It is easier to notice it on low-ish frequencies(60-350hz maybe?), it is a real issue. I have been sticking to 8th order and lower since that time. Sometimes make setups with different slope xo's, and just fast switch between them to find the one that works best. Sometimes you got to mix types and orders.

Last edited by KaffiMann; 19th March 2018 at 07:43 AM.
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Old 19th March 2018, 09:48 AM   #88
33Polkhigh is offline 33Polkhigh  United States
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Quote:
Originally Posted by KaffiMann View Post
I had ringing on a sub once, it was really bad. Using 16th order filters and higher.
Worst was Elliptic. Butterworth and also Bessel worked reasonably well. It is easier to notice it on low-ish frequencies(60-350hz maybe?), it is a real issue. I have been sticking to 8th order and lower since that time. Sometimes make setups with different slope xo's, and just fast switch between them to find the one that works best. Sometimes you got to mix types and orders.
A number of studies have shown that we aren't very sensitive to phase, but we are sensitive to off axis problems like lobing. So a steep slope is better, and sort of reduces the overall affect of the crossover, especially in an active system.

Ringing can occur though, in any type of steep slope. Possibly using a variable slope in the crossover would help.
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Old 19th March 2018, 08:10 PM   #89
KaffiMann is offline KaffiMann  Norway
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I understand what you are saying. And am very familiar with the pro-steep filters arguments you use.

Just mentioning that steep slopes are not always the best answer.
You have to hear bad ringing in order to properly identify it. I had no clue, just messing around trying steep filters because it was "all the rage", experimenting. After some days/weeks I try to go back to my old settings with the "slow" filters just to laugh at my vast improvement, notice this really weird effect on my subs first, after switching back and forth, thinking "they are not supposed to sound like this?", after noticing it there and identifying the problem, I found the same problem present in my other filters as well.
What it sounds like is heavily dependent of the frequency the filter works on. It sort of changes in "speed and pitch", do not know how to describe it.

If you do not have these problems then good for you.
I need more testing to get the filters right, just choosing a frequency and setting the steepest filters does not always give optimal results.

It is easy to "shrug it off", "just my imagination playing tricks". You can fool yourself into "knowing" you are making improvements, but maybe you are getting further away from your goal. Quick changing filter settings while listening to varied music is my solution. I rarely choose more than 48db/oct after testing.

I know I was fooling myself into thinking it was better.

Last edited by KaffiMann; 19th March 2018 at 08:19 PM.
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Old 19th March 2018, 08:38 PM   #90
33Polkhigh is offline 33Polkhigh  United States
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Kaffiman, thanks. I wouldn't go steep on a sub anyways since low frequencies are more affected and overlap isn't an issue (unless you have distortion problems). Do you think a variable slope that gets steeper and steeper would help with the potential ringing? I was looking into this.
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