Old 06-22-2017, 04:28 PM   #1
Tod
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Default ReaEQ (Hi & Lo pass filters) ?

Hi all, from what I understand, the ReaEQ Hi & Lo pass filters have a slope of 6dB per octave.

The question is, if I combine either 3 Hi or 3 Lo pass filters, all at the same exact freq, would that give me a slope of 18dB per octave, and if so, what quality would it be in comparison to a good EQ that has 18dB per octave Hi/Lo pass filters.

I think I've seen this question come up before, but I don't remember the outcome.
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Old 06-22-2017, 04:41 PM   #2
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Hi Tod,

Yep. Stacking filters at the same frequency does increase the slope exactly as you say. I do that regularly with ReaEQ and have not had any issues with sound quality. ReaEQ is pretty transparent and is my go-to EQ when I don't need or want character.

I would love to see Cockos add a feature to adjust the slope of a single band though and that has been requested very frequently.
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Old 06-22-2017, 04:58 PM   #3
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Originally Posted by ReaDave View Post
Hi Tod,

Yep. Stacking filters at the same frequency does increase the slope exactly as you say. I do that regularly with ReaEQ and have not had any issues with sound quality. ReaEQ is pretty transparent and is my go-to EQ when I don't need or want character.

I would love to see Cockos add a feature to adjust the slope of a single band though and that has been requested very frequently.
Thanks a lot Dave, I really didn't know, so it's a sigh of relief because ReaEQ is also my main EQ, there's literally nothing you cant do with it. I've tried many and even got some fairly expensive ones, but they just don't have any where near the flexibility that ReaEQ does.
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Old 06-22-2017, 05:59 PM   #4
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If stacking software filters like this work like the real thing then it also means the phase shift will be three times larger.
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Old 06-22-2017, 06:24 PM   #5
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I sure wish somebody would explain to me how changing the bandwidth parameter doesn't do about the same thing. Sure seems to change the slope from everything I've seen. How to equate bandwidth to filter poles and/or Q so that you could dial it in to match a specific slope is a bit more questionable, but...



Edit - But I think stacking filters like the OP suggests is going to change the actual cutoff of the filter, because it will be a total of 9db down at whatever frequency you've chosen, rather than -3. In an actual 3-pole filter, the cutoff would still be the -3db point.
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Old 06-22-2017, 06:42 PM   #6
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Quote:
Originally Posted by ashcat_lt View Post
I sure wish somebody would explain to me how changing the bandwidth parameter doesn't do about the same thing. Sure seems to change the slope from everything I've seen. How to equate bandwidth to filter poles and/or Q so that you could dial it in to match a specific slope is a bit more questionable, but...



Edit - But I think stacking filters like the OP suggests is going to change the actual cutoff of the filter, because it will be a total of 9db down at whatever frequency you've chosen, rather than -3. In an actual 3-pole filter, the cutoff would still be the -3db point.
Hi ashcat, I've tried the bandwidth before, but it causes a rather skewed visual line in ReaEQ, stacking them does not do that. But I don't know the real significance of that. Like you, I'd be curious too, to know how that works.
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Old 06-25-2017, 10:41 AM   #7
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Quote:
Originally Posted by ashcat_lt View Post
I sure wish somebody would explain to me how changing the bandwidth parameter doesn't do about the same thing.
This is my question as well.
What's the difference of creating 24db/oct with bandwidth vs. stacking 2 filters?

(I always grab the bandwidth-knob to get to where I want.)
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Old 06-22-2017, 06:35 PM   #8
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Quote:
Originally Posted by C-H View Post
If stacking software filters like this work like the real thing then it also means the phase shift will be three times larger.
Thanks C-H, so are you saying that stacking the 3 filters will cause a phase shift that the real thing does not have, or that it will just end up the same as the real thing?
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Old 06-22-2017, 07:59 PM   #9
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Quote:
Originally Posted by Tod View Post
Thanks C-H, so are you saying that stacking the 3 filters will cause a phase shift that the real thing does not have, or that it will just end up the same as the real thing?
A 'real' 2-pole filter have twice the phase shift of a 1-pole filter.
Almost sure about this... it does make sense.

It is also true that stacking 3 x filter each with a cutoff freq at Fc with not produce a 3-pole filter with the same Fc. It will be lower.

Edit:
This applies to hardware filters. I don't know how ReaEQ is programmed to handle this but I would assume it is supposed to react like a real filter unless some Voodoo is made with zero-phase shift filters.
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Old 06-23-2017, 11:55 AM   #10
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Quote:
Originally Posted by C-H View Post
If stacking software filters like this work like the real thing then it also means the phase shift will be three times larger.
This.

Often not an issue. ie. The phase artifacts would pale compared to leaving the frequency content unbalanced.

But if you're parallel processing something, ReaEQ would likely be no go. You'd end up comb filtering content you wished to preserve.
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Old 06-23-2017, 01:07 PM   #11
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Originally Posted by serr View Post
This.

Often not an issue. ie. The phase artifacts would pale compared to leaving the frequency content unbalanced.

But if you're parallel processing something, ReaEQ would likely be no go. You'd end up comb filtering content you wished to preserve.
We're on the same page. That's pretty much exactly what I was getting at a few posts up.....
http://forum.cockos.com/showthread.p...89#post1858289
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Old 06-23-2017, 01:18 PM   #12
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Okay, I just tested with pink noise with a 3dB slope, and this is what I got.

Input signal to Span is -27dB, without any EQ, ReaEQ was bypassed.

With one tab set to 200hz Hi Pass, this is what I got.

Input = -27dB
200Hz = -30.2dB (Down 3.2dB from the input)
100Hz = -39.1dB (Down 9.1dB from 200Hz)
Total = 12.3dB

With two tabs set to 200hz Hi Pass, this is what I got.

Input = -27dB
200Hz = -33.8dB (Down 6.8dB from the input)
100Hz = -51.1dB (Down 17.3dB from 200Hz)
Total = 24.1dB

With margin for error I think we can safely say ReaEQ's hi/lo pass filters are 12dB per octave.

Regarding the phase, I turned it on but I don't understand what I'm seeing so I can't comment on that.
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