Channel EQ (Reason classic) HPF adding gain?

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moggadeet
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Post 21 Dec 2020

Good morning,

I found this situation today while using the Channel EQ as an insert FX. Why are there 4dB peak more after the HPF? The filter is taking out the whole DC component that the Scream4 adds, so definitely should be showing less and AFAIK it is not a resonant filter and thus does not boost any frequency, right?

If I bypass the Channel EQ the final Selig Gain shows -14dB peak. If I disable the HPF same effect. If I set the upper Selig Gain to mono, the value of the final Selig Gain goes to -11dB peak.
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Jackjackdaw
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Post 21 Dec 2020

I found that the channel EQ insert has a different sound than the SSL EQ with the same settings. I did it by ear but it was definitely different.

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antic604
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Post 21 Dec 2020

Interesting & good catch, because it probably doesn't SOUND louder, right?

What's weirder is that both in & out displays on 2nd Selig Gain definitely don't show -10dB but rather between -14 and -20dB with a difference between L & R channels (absent on 1st Gain), which would suggest some phasing is introduced by HPF? Your observation that results are closer in Mono would confirm that.

Definitely send this to support!
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antic604
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Post 21 Dec 2020

Jackjackdaw wrote:
21 Dec 2020
I found that the channel EQ insert has a different sound than the SSL EQ with the same settings. I did it by ear but it was definitely different.
Could it be because of signal processing order?

By default Mixer goes Dynamics -> EQ -> Inserts:

Image

whereas if you'd put Channel EQ after the Insert FX, like the OP did, the order would be reversed.
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moggadeet
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Post 21 Dec 2020

antic604 wrote:
21 Dec 2020
Jackjackdaw wrote:
21 Dec 2020
I found that the channel EQ insert has a different sound than the SSL EQ with the same settings. I did it by ear but it was definitely different.
Could it be because of signal processing order?

By default Mixer goes Dynamics -> EQ -> Inserts:

Image

whereas if you'd put Channel EQ after the Insert FX, like the OP did, the order would be reversed.
Thanks for the idea, but I have no dynamics applied and no SSL EQ. I swapped the processing order anyway, still getting -14dB and -10dB.

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moggadeet
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Post 21 Dec 2020

antic604 wrote:
21 Dec 2020
Interesting & good catch, because it probably doesn't SOUND louder, right?

What's weirder is that both in & out displays on 2nd Selig Gain definitely don't show -10dB but rather between -14 and -20dB with a difference between L & R channels (absent on 1st Gain), which would suggest some phasing is introduced by HPF? Your observation that results are closer in Mono would confirm that.

Definitely send this to support!
You mean the Selig Gain in the middle? Yes, that one I use to gain-match the Scream4.

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antic604
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Post 21 Dec 2020

moggadeet wrote:
21 Dec 2020
Thanks for the idea, but I have no dynamics applied and no SSL EQ. I swapped the processing order anyway, still getting -14dB and -10dB.
This was in reply to @Jackjackdaw :)
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antic604
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Post 21 Dec 2020

moggadeet wrote:
21 Dec 2020
You mean the Selig Gain in the middle? Yes, that one I use to gain-match the Scream4.
Yeah, sorry - I didn't see then 1t Selig Gain, so when I'm referring to 1st and 2nd I meant 2nd and 3rd respectively.
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selig
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Post 21 Dec 2020

This is a documented "feature" of a high pass filter.
https://www.soundonsound.com/sound-advi ... eem-louder
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moggadeet
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Post 21 Dec 2020

selig wrote:
21 Dec 2020
This is a documented "feature" of a high pass filter.
https://www.soundonsound.com/sound-advi ... eem-louder
Thanks a lot Giles! It makes sense now :puf_smile:

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miscend
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Post 21 Dec 2020

Why does Scream4 add DC anyway? They should fix it, maybe add a switch at the back.

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antic604
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Post 21 Dec 2020

selig wrote:
21 Dec 2020
This is a documented "feature" of a high pass filter.
https://www.soundonsound.com/sound-advi ... eem-louder
So it is a phase problem, like I was speculating.

Thanks Gilles!!! :thumbs_up:
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diminished
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Post 21 Dec 2020

antic604 wrote:
21 Dec 2020
selig wrote:
21 Dec 2020
This is a documented "feature" of a high pass filter.
https://www.soundonsound.com/sound-advi ... eem-louder
So it is a phase problem, like I was speculating.

Thanks Gilles!!! :thumbs_up:
no, it's a property of the filter implementation being used, which is probably a Chebyshev type I design.
https://en.wikipedia.org/wiki/Chebyshev_filter
They have a ripple near the crossover frequency and since it's a lowpass filter and the most energy is in the low frequencies, you can notice it on the meter.
https://upload.wikimedia.org/wikipedia/ ... 29.svg.png
:reason: Most recent track: resentment (synthwave) || Others: on my YouTube channel •ᴗ•

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antic604
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Post 21 Dec 2020

diminished wrote:
21 Dec 2020
antic604 wrote:
21 Dec 2020


So it is a phase problem, like I was speculating.

Thanks Gilles!!! :thumbs_up:
no, it's a property of the filter implementation being used, which is probably a Chebyshev type I design.
https://en.wikipedia.org/wiki/Chebyshev_filter
They have a ripple near the crossover frequency and since it's a lowpass filter and the most energy is in the low frequencies, you can notice it on the meter.
https://upload.wikimedia.org/wikipedia/ ... 29.svg.png
So how is that a "no"?

Looking at the symptoms I speculated it's a phase shift. AFAIK most filters do that, unless special, computationally expensive methods are applied, like in Pro-Q3 for example. So it stands to reason that our "SSL" filters were not doing that, being available on all tracks 10 or so years ago, when CPUs were much less powerful.
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diminished
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Post 21 Dec 2020

antic604 wrote:
21 Dec 2020
diminished wrote:
21 Dec 2020


no, it's a property of the filter implementation being used, which is probably a Chebyshev type I design.
https://en.wikipedia.org/wiki/Chebyshev_filter
They have a ripple near the crossover frequency and since it's a lowpass filter and the most energy is in the low frequencies, you can notice it on the meter.
https://upload.wikimedia.org/wikipedia/ ... 29.svg.png
So how is that a "no"?

Looking at the symptoms I speculated it's a phase shift. AFAIK most filters do that, unless special, computationally expensive methods are applied, like in Pro-Q3 for example. So it stands to reason that our "SSL" filters were not doing that, being available on all tracks 10 or so years ago, when CPUs were much less powerful.
I'm currently looking for the post where Mattias said himself that there is a nice little boost (he spoke positively about it, I agree) that "comes" with the filter by default. So it's not just some random occurance of frequencies happening to be in a minimum of a lower frequency, but it's the filter design
:reason: Most recent track: resentment (synthwave) || Others: on my YouTube channel •ᴗ•

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selig
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Post 21 Dec 2020

Jackjackdaw wrote:
21 Dec 2020
I found that the channel EQ insert has a different sound than the SSL EQ with the same settings. I did it by ear but it was definitely different.
I cannot confirm that at all - at every setting I tested on the EQ and the filters, they are spot on down to the 100th of a dB.
I mean, there really isn't any reason why they should be different if they copied the code, and it appears that's exactly what they have done.
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Jackjackdaw
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Post 22 Dec 2020

selig wrote:
21 Dec 2020
Jackjackdaw wrote:
21 Dec 2020
I found that the channel EQ insert has a different sound than the SSL EQ with the same settings. I did it by ear but it was definitely different.
I cannot confirm that at all - at every setting I tested on the EQ and the filters, they are spot on down to the 100th of a dB.
I mean, there really isn't any reason why they should be different if they copied the code, and it appears that's exactly what they have done.
I will take your word for it. My test was far from scientific!

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selig
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Post 22 Dec 2020

I say "let's take a look" and see for ourselves what is going on. Will be testing an assortment of Reason/RE HP filters to see their responses (frequency and phase), plus run some white noise and see if the peak level changes.
All filters at 100Hz, testing 12 and 24 dB/Oct where possible (and 18 dB/Oct where possible because of the SSL HP filter).

First up, peak level change. (note, I'm rounding to the nearest dB so there MAY be as much as 1dB difference)
Pulveriser 12: +2dB
Thor 12: +2dB
SSL 18: +2dB
Neutron 24: +2dB
Neutron 12: +2dB
Black Knight 12: +2dB
Unifylter 12: +3dB
ColoringEQ 12: +2dB
ColoringEQ 18: +2dB
ColoringEQ 24: +2dB
[ColoringEQ 36, 48: +3dB]
GQ7 A12, A24, B12: +2dB
[GQ7 B24, B36, B48: +3dB]
[GQ7 A60, A72, A84, A96: +4dB]

For fun I measured ALL the main CEQ and GQ7 types to see where they fell.
Bottom line, HP filters add gain when cutting.
Further, the steeper slopes have more phase shift, but still output the same +2dB peak level change (as do the filters with bumps vs no bumps), which strongly suggests it is the phase shift which is affecting things more than any other factor.
Here is a screen shot of ALL the filters that boosted by 2dB:
Image
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visheshl
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Post 22 Dec 2020

i wonder are all producers so clinical about their production to notice a 2db difference here n there...?

genuine question...i go by the ear when mixing different plugins alter the sound differently...some eq plugin might be transparent but the other may add a few dbs, but i dont care as long as it sounds right to me....is music such a scientific subject that if a plugin adds a few dbs it makes a difference or is music still an artform ?

im curious...are you all concerned if a plugin is scientifically accurate or do you go by the ear ?

really curious

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miscend
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Post 22 Dec 2020

visheshl wrote:
22 Dec 2020
i wonder are all producers so clinical about their production to notice a 2db difference here n there...?


Maybe not but that's why we use plugins like Selig gain. I also use a VST3 called Gain match. For mixing it is good practice to gain match plugins because some of them trick you by adding a few dbs of gain. You may be surprised to find out after gain matching that some plugins don't actually add anything to that particular mix. It's just our senses interpreting louder as automatically better. Even a 1db boost is enough to alter our perception.

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friday
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Joined: 17 Jan 2015

Post 22 Dec 2020

[Edit] So the SSL HP is a 18dB filter? YES - CHECKED THE MANUAL - HP 18 / LP 12

GQ7 is my go to HP Filter, but now I don't know how to interpret that +4dB for my future workflow?

Do I get bether results with fabfilter (not the phase linear mode, some engineers told me that it has some kind of ringing in the transients)?
Last edited by friday on 24 Dec 2020, edited 1 time in total.

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moggadeet
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Location: Stuttgart, Germany

Post 23 Dec 2020

selig wrote:
22 Dec 2020
I say "let's take a look" and see for ourselves what is going on. Will be testing an assortment of Reason/RE HP filters to see their responses (frequency and phase), plus run some white noise and see if the peak level changes.
All filters at 100Hz, testing 12 and 24 dB/Oct where possible (and 18 dB/Oct where possible because of the SSL HP filter).

First up, peak level change. (note, I'm rounding to the nearest dB so there MAY be as much as 1dB difference)
Pulveriser 12: +2dB
Thor 12: +2dB
SSL 18: +2dB
Neutron 24: +2dB
Neutron 12: +2dB
Black Knight 12: +2dB
Unifylter 12: +3dB
ColoringEQ 12: +2dB
ColoringEQ 18: +2dB
ColoringEQ 24: +2dB
[ColoringEQ 36, 48: +3dB]
GQ7 A12, A24, B12: +2dB
[GQ7 B24, B36, B48: +3dB]
[GQ7 A60, A72, A84, A96: +4dB]

For fun I measured ALL the main CEQ and GQ7 types to see where they fell.
Bottom line, HP filters add gain when cutting.
Further, the steeper slopes have more phase shift, but still output the same +2dB peak level change (as do the filters with bumps vs no bumps), which strongly suggests it is the phase shift which is affecting things more than any other factor.
Here is a screen shot of ALL the filters that boosted by 2dB:
Thanks for the informative post!

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antic604
Posts: 655
Joined: 02 Apr 2020

Post 23 Dec 2020

visheshl wrote:
22 Dec 2020
i wonder are all producers so clinical about their production to notice a 2db difference here n there...?

genuine question...i go by the ear when mixing different plugins alter the sound differently...some eq plugin might be transparent but the other may add a few dbs, but i dont care as long as it sounds right to me....is music such a scientific subject that if a plugin adds a few dbs it makes a difference or is music still an artform ?

im curious...are you all concerned if a plugin is scientifically accurate or do you go by the ear ?

really curious
I'm like you in this regard ("it's good if it sounds good") but you also have people like @friday above whose world seem to have now shattered and he's lost after learning there's slight volume boost using HPF ;) :lol:

So I guess it's a spectrum, :)
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friday
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Post 23 Dec 2020

antic604 wrote:
23 Dec 2020
I'm like you in this regard ("it's good if it sounds good") but you also have people like @friday above whose world seem to have now shattered and he's lost after learning there's slight volume boost using HPF ;) :lol:

So I guess it's a spectrum, :)
You are right, I am an over analytical person.

But I am also in contact with some very experienced engineers (mastering engineers, producers) and they care about every dB on the master, to get competitive mixes. That's why I'm interested what happens in the whole chain of saturation, compression and summing, if it adds +4dB when I later deside to insert a HP at the beginning of this chain.

If no one would care, EQ's wouldn't have a phase linear mode ;-)
Last edited by friday on 23 Dec 2020, edited 1 time in total.

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Jackjackdaw
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Post 23 Dec 2020

It's fine to care. It's fine to not care. But why would you question someone for wanting to go deep into anything? Knowledge is power!

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