EQ's- The Evil Within

[fader8]

Hello!

Well, for my own gratification, I've been doing some EQ plug-in testing and in particular looking at artifacts. Here's my results thus far and I'll be adding various other measurment types to it as I get time. I still need to get to the Pro Tools stuff too.
So far, I've been looking at filter ringing, but I've started to run phase plots too. There's one for the PSP MasterQ so far, link at bottom of page. Any suggestions for useful tests are welcome. Some of you may find this of interest.

fader8's EQ Artifacts Page

[PeterSturm]

That is interesting.
What does it mean to you?

[fader8]

Originally Posted by PeterSturm

What does it mean to you?

That is a very good question, actually. I'd have to say that it's partly just curiousity. After you do this stuff long enough, you get to where you use certain tools for things, you know, like you latch on to a favorite eq for snare and a favorite comp for bass, etc. But after a while you get curious as to why you happen to like that sound and what it is that's getting you there.

The other thing is that I spent a huge chunk of my career in audio/acoustic test and measurement, so I guess I just can't leave it alone! But oh! You're probably asking what the data means to me, eh? Well, not much, yet anyway. There's not really enough there to draw any conclusions on. These are all decent products, but not one of them is decent on everything. The data is insightful, although it's only one minute aspect of a bigger picture as there are so many other parameters to look at. There's a bit of black art in things like filter design, so it's partly my appreciation for those who endeavor to do it well.

There's another aspect. Doing tests like this can be a great insomniac pastime. Beats the hell out of watching bad television! So I'll plug at it once in a while and who knows, maybe something of interest will come out of it.
Cheers.

[kidhandsome]

interesting test. I'm surprised how much artefacts there are with the sonnox stuff.

Good to see the Sonalksis eq's did well.

[fader8]

Originally Posted by kidhandsome

I'm surprised how much artefacts there are with the sonnox stuff.

Me too, but switch it to it's Type 4 setting and it's the best of the bunch. Go figure.

[fader8]

And for all you true hardcore filter geeks, check out fader8's Cambridge Filter Page!

[jdtrbn]

I'm really curious about the phase shifts, hope to see them soon.
Epure looks so funny, and still I've understood it's quite liked as a mastering EQ.

I wonder how to interpret those waveforms though. I'd guess pre-echo is more critical than "echo", because the backward masking effect is weaker than forward masking. Or maybe I'm way off.

[bcgood]

This is one of my favorite plug in eq's.

[fader8]

Originally Posted by jdtrbn

I'm really curious about the phase shifts, hope to see them soon.
Epure looks so funny, and still I've understood it's quite liked as a mastering EQ.

Well, keep in mind that all those plots were done with a 6dB cut, which you'd rarely hit in a mastering situation.

I wonder how to interpret those waveforms though. I'd guess pre-echo is more critical than "echo", because the backward masking effect is weaker than forward masking. Or maybe I'm way off.

Depends what you're doing, eg pre-echo can really smear up a snare.

I posted some phase plots for a few more EQ's. When I get a chance, I'll play with comparing gain-Q coupling and filter symmetry. http://fader8.com/audioblog/

[PMoshay]

Very interesting...........

I like not knowing, sometimes ignorance is bliss.
One time i tracked a whole song with a broken eq....... and i loved it.

If you listen to AC/DC "Back in Black", you can hear the drum punch in's in the choruses......the snare sound changes in each section and the snare is a different tuning too...........

They cheated!........ but i still love it!

Thanks for the posting the info, it is interesting to see. But now i'm gonna just feel bad when i eq though....

[sanddigger1]

Thanks for the info. You've tested Izotope Ozone, but was it in digital linear phase mode, or in analogue emulation one ?

[fader8]

Originally Posted by sanddigger1

Thanks for the info. You've tested Izotope Ozone, but was it in digital linear phase mode, or in analogue emulation one ?

That was the analog mode. Thanks for bringing this up, I'll have to plot it's other modes.

[Alexey Lukin]

The amount and shape of filter ringing is directly related to the filter frequency response and type of phase response. For example, for linear-phase filters, pre-ringing is equal to post-ringing, and they are completely determined by the filter frequency response. For minimum-phase filters, pre-ringing is minimal or absent, and post-ringing is maximal, and again they are completely determined by the frequency response (because phase response is also determined by the frequency response).

As a general rule, ringing occurs near discontinuities or bends in frequency response (and phase response). So, having smoother frequency response produces less ringing. Ringing should not be considered only as "undesirable artifact" of a filter, because it just reflects the desired frequency response. If the required frequency response is completely specified, there's no way to reduce the amount of ringing: you can only trade pre-ringing for post-ringing by choosing the type of filter phase response.

[fader8]

Originally Posted by Alexey Lukin

The amount and shape of filter ringing is directly related to the filter frequency response and type of phase response.

Agreed. It is an inevitable fact of life. What I find of interest is that given an identical frequency response and phase response, filters of different manufacture can have differing ringing characteristics.

[Alexey Lukin]

Usually these differences are caused by small deviations of frequency responses or by different types of phase response.

[fader8]

Originally Posted by Alexey Lukin

Usually these differences are caused by small deviations of frequency responses or by different types of phase response.

While that's a contributor, it's not universally true. Quite a few of the "minimum phase" EQ's have identical phase response for a calibrated identical frequency response. Yet they can display quite a variance in their ringing characteristics.