Why does HPF with an EQ increase amplitude?
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- KVRian
- Topic Starter
- 746 posts since 27 Nov, 2011
Hi, I just discovered something that I think is really weird. I was comparing EQ plugins and loaded in a drum break that fills out the frequency range. I loaded up an EQ and set one of the bands to high pass, and high-passed it up to ~3khz. To my surprise, this increased the output level by 4db. I'm surprised because I thought that I'm removing energy from the signal by high passing. The break is the only thing I have loaded in the DAW, so it's not revealing some masking that was going on. Clearly I don't understand the effect that an EQ has on a signal. Can someone please explain to me why the output level would go up when I high-pass filter a signal?
Last edited by padillac on Sun Feb 24, 2013 3:09 pm, edited 1 time in total.
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- KVRian
- Topic Starter
- 746 posts since 27 Nov, 2011
there is no resonance (or at least, no controllable resonance). It's a 24db HPF w/ cutoff set to ~3khz.
I've just done some reading on phase shift and it doesn't help me that much. Hopefully someone is able to go into a bit more detail as to what exactly happens to increase the amplitude of the signal even though I'm supposedly removing most of the energy from it.
I've just done some reading on phase shift and it doesn't help me that much. Hopefully someone is able to go into a bit more detail as to what exactly happens to increase the amplitude of the signal even though I'm supposedly removing most of the energy from it.
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- KVRAF
- 6828 posts since 28 Apr, 2004 from france
I can't go too much into techie stuff, but i'm aware that it is a known and normal behaviour.
Low freq has most energy, so cutting it a bit will let more room for other frequencies to breathe, and therefore you get a small volume increase.
Low freq has most energy, so cutting it a bit will let more room for other frequencies to breathe, and therefore you get a small volume increase.
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- KVRAF
- 6426 posts since 22 Jan, 2005 from Sweden
Peak meters don't measure energy as far as I know, just peaks.
My guess is that DC level change, and you might have to remove that to get signal back to normal - or it had DC before since I believe shelving HP filters remove DC.
Maybe the plugin has such an option?
Just guessing....
My guess is that DC level change, and you might have to remove that to get signal back to normal - or it had DC before since I believe shelving HP filters remove DC.
Maybe the plugin has such an option?
Just guessing....
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maxxxter maxxxter https://www.kvraudio.com/forum/memberlist.php?mode=viewprofile&u=1
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- KVRian
- Topic Starter
- 746 posts since 27 Nov, 2011
hrm. I still don't get it. Low freq has the most energy, so why does cutting most of the energy increase the amplitude of the signal? I would expect the amplitude to be reduced if I remove most of the energy. Obviously I'm *not* removing most of the energy, it's just being shifted elsewhere (phase shift, I guess?).sinkmusic wrote:I can't go too much into techie stuff, but i'm aware that it is a known and normal behaviour.
Low freq has most energy, so cutting it a bit will let more room for other frequencies to breathe, and therefore you get a small volume increase.
When I look at the signal on a spectrum analyzer, the high end frequencies peak at about -20db before EQing. After I high pass it, the high end *still* peaks at -20db. Only now I can't even see any low-end energy on the spectrum because it's all been cut out. I guess I could understand the amplitude going up if the high end frequencies also got louder, but they don't. My best guess at this point is that somehow all of the low-end energy has now been shifted into VERY high-end energy beyond my hearing (and beyond my spectrum analyzer's graph).
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- KVRian
- Topic Starter
- 746 posts since 27 Nov, 2011
cutting bass increases the amplitude a little. boosting bass increases the amplitude a lot. beats me why (mostly cutting..)maxxxter wrote:if this is a normal behavior, does that mean that adding bass to the signal should then lower the amplitude? If not, why? Why does it work only one way around?
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- KVRian
- Topic Starter
- 746 posts since 27 Nov, 2011
I specifically left that info out because I don't think it matters...it happens with Live's built-in EQ as well as three separate commercial plugin EQs. I don't believe it's a bug in the EQs, I believe it to be a side-effect of EQing...I just wish I had any clue as to why.kylen wrote:Very interesting...
which EQ is it - I'd like to see oddity that myself also.
What else is in the chain, just incoming audio & EQ & metering?
Nothing else in the chain. No other tracks. One incoming audio signal & EQ & meter.
- KVRAF
- 5564 posts since 13 Jan, 2005 from the bottom of my heart
HPFs always increase the peak amplitude, and yes its phase shift. there's nothing you can do about it. normally dont run your leves too hot and lower the filter slope if possible (lower filter slope = less phase shift). also you can use a linear phase eq.
Whoever wants music instead of noise, joy instead of pleasure, soul instead of gold, creative work instead of business, passion instead of foolery, finds no home in this trivial world of ours.
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- KVRian
- Topic Starter
- 746 posts since 27 Nov, 2011
linear phase mode still increases the amplitude.
I appreciate the folks trying to help, but so far I've seen no explanation of why "phase shift" changes the amplitude. If anyone is able to explain where the "cut" energy *goes* and where the apparent new energy *comes from* I will be a happy camper.
I appreciate the folks trying to help, but so far I've seen no explanation of why "phase shift" changes the amplitude. If anyone is able to explain where the "cut" energy *goes* and where the apparent new energy *comes from* I will be a happy camper.
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- KVRAF
- 1724 posts since 10 Feb, 2008 from Berlin, Germany
We already had a few threads with that topic.
Here some answers:
http://www.kvraudio.com/forum/viewtopic ... 18#3966518
But to answer your question:
There does not come energy, if you cut out bass.
But because of the heavy ringing (from EQing in low frequency areas), your waveform gets another form and (usually) higher peaks.
So your signal peaks higher, but stays at the same (perceived) loudness (or even gets more quiet).
This problem is usually a lot weaker with LP EQs.
Here some more words on it:
http://www.kvraudio.com/forum/viewtopic ... 96#4220396
Here some answers:
http://www.kvraudio.com/forum/viewtopic ... 18#3966518
But to answer your question:
There does not come energy, if you cut out bass.
But because of the heavy ringing (from EQing in low frequency areas), your waveform gets another form and (usually) higher peaks.
So your signal peaks higher, but stays at the same (perceived) loudness (or even gets more quiet).
This problem is usually a lot weaker with LP EQs.
Here some more words on it:
http://www.kvraudio.com/forum/viewtopic ... 96#4220396
Last edited by Nokenoku on Sun Feb 24, 2013 4:28 pm, edited 2 times in total.
- KVRAF
- 5564 posts since 13 Jan, 2005 from the bottom of my heart
my english is to bad to explain but i found a nice explaination from a producer called Lagerfeldt:padillac wrote:linear phase mode still increases the amplitude.
I appreciate the folks trying to help, but so far I've seen no explanation of why "phase shift" changes the amplitude. If anyone is able to explain where the "cut" energy *goes* and where the apparent new energy *comes from* I will be a happy camper.
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It's the phase relations that change.
The original waveform (your mix) consists of a variety of frequencies that interact and constitute a whole.
When you use an equalizer you're not only changing the amount of gain in a particular frequency area, but you're also changing the phase and therefore the timing between the various frequencies.
This causes the various frequencies to interact in a different way that may or may not lead to a positive change (peak) as the frequencies shift - even though you're cutting. Remove enough though and you'll see the peak level go down again, but that's not the solution of course.
Most equalizers are so-called minimum phase and have this natural and normally desirable behaviour. Quite often when you're equalizing you're not just changing the amount of gain in a particular area, but you're trying to obtain the right phase response.
However, you can use a phase linear equalizer to offset the relative phase changes. In your case you'll observe almost no peak change, but still get the low cut you're looking for. Linear phase is no magic bullet though, and you'll probably hear some transient blurring caused by pre-filter ringing, which is an unwanted side-effect of linear phase technology. This is one of the reasons why linear phase is not the first choice for many engineers.
Logic Pro has a bundled linear phase equalizer, but you can also get the DMG Audio EQuality and switch between modes on the fly.
Whoever wants music instead of noise, joy instead of pleasure, soul instead of gold, creative work instead of business, passion instead of foolery, finds no home in this trivial world of ours.