phase-shifts / time-based artifacts

[vogler]

hey!
i've just read a very nice article by Blue Bear about EQ (http://www.bluebearsound.com/articles/eqnotes.htm).

could anyone explain me what it means (physical mean) exactly?
" The addition of EQ into the signal chain always results in "some" compromise of the waveform by introducing phase-shifts (time-based artifacts that can results in comb-filtering of the waveform) - especially when boosting frequencies."
How it happens?
tnx
Vogler

 

[AlChuck]

Because any adjustment of frequencies has to happen after the signal itself is created

 

[easychair]

Basically, equalizers work by adding a filtered signal to the original. Depending on the amount of phase shift (delay) the filtered signal has, the desired frequency is reduced or boosted. The amplitude of the filtered signal versus the original determines how much cut or boost happens.

The problem is that first, at the desired frequency, the two signals do not combine or cancel perfectly. Second, the filters aren't perfect, and affect frequencies on either side of the center frequency.

The comb filtering problems result from the interactions of the original signal and the filtered signal. How audible they are depends on the amount of cut or boost applied, and the quality of the eq. The problems are more evident while boosting, because, well, the boosted frequencies and phase anomalies are made louder, instead of softer, which happens when you cut.

Digital eqs suffer from the same problems, though for different reasons, I suspect.

Here is a link to an eq shootout, with some of the best (and not so best) graphic eqs in the world. Various amounts of cut and boost are applied, and frequency response and phase tracings are captured using SIA Smaart software. It is interesting to note that even the absolute top of the line analog and digital eqs have these characteristics to varying degrees.

Bink's eq shootout

 

[vogler]

Because any adjustment of frequencies has to happen after the signal itself is created

i know... i was thinking about negative results of EQ for sound.

Thanks Easychair for your full reply!! Thant's what i needed.

 

[regebro]

Basically, equalizers work by adding a filtered signal to the original. Depending on the amount of phase shift (delay) the filtered signal has,

Uhm. Phase shift and delay is not the same thing. Otherwise you are right, although when you say "amount of phase shift" it sounds like you are modifying it, while in fact that phase shift to will be either 0 (boosting) or 180 (cutting). At least that's how I did it in school.

Introducing ANY kind of effect will give you phase issues, basically. I'm a bit wary of Bluebears explanation that cutting works better than boosting because of phase issues. It seems counter-intuitive to me. I think it generally seems to sit better in a mix if you cut out the bad frequences instead of bossting the good, because the resulting sound will have a narrower fottprint and wont step on other sounds as much. But that's just me guessing.

Edit: Or maybe not. filters do cause phasing, espesially in the "sloping" areas. If you cut, these sloping areas will be less loud than if you boost. So maybe Bluebear is right (as usual).