How do you judge an EQ?

[Kingston]

just a thought, but can we clear up the terminology here just a bit?

A lot of people here seem to be talking of all these bogstandard biquads as minimum phase filters. Let's not do that please. While it's technically true, this far the term minimum phase filter has referred to the case of something "optimised" between linearphase and phase warp. It produces the mandatory delay, while the biquads etc orfanids don't.

1. linearphase filters (self-explanatory)
2. phase warping filters: everything that produces no latency. This includes most of the digital and nearly all of analog filters we have had since the dawn of days.
3. mimimun phase filters, something between 1 and 2. (sometimes called optimum phase filter)

[Christian Budde]

1. linearphase filters (self-explanatory)
2. phase warping filters: everything that produces no latency. This includes most of the digital and nearly all of analog filters we have had since the dawn of days.
3. mimimun phase filters, something between 1 and 2. (sometimes called optimum phase filter)

I don't agree here: The definition for minimum phase (see http://en.wikipedia.org/wiki/Minimum_phase) also equals the fact that they have minimum group delay = zero latency

[Democritus]

There are 3 types of eq: Good, Bad and Regular

The good comes in 2 types: The ones that solves problems without changing your original sound so much and the ones that solves problems changing your original sound or simply changes your original sound in a nice way when there are no problems to solve.

The bad ones neither solves any problem nor color or changes the sound in a nice way.

Regular ones only solves gross problems in a boring way.

[Barbarossa]

I also can't agree. In electrical engineering it is clearly defined what minimum phase filters are. This is a well defined technical term.
Kingston, what i don't understand: you say that more phase shift preserves transients better.
How can that be? Any phase shift causes a distortion of impulses, since the different frequencies building up the impulse, are shifted against each other. What you tell me, doesn't fit into the whole signal-theory i learned and therefore i still don't understand, why the system with the higher phase-shift, this MysteryEQ preserves the transients better, while the phase-minimum WavelabQ system smears them.

[bmanic]

Ok. I'll try to make an example for tomorrow.
We'll match IRs before, so it will be orange with orange and we could focus better on this 'transients' thing.
It's good even a filter? A not labeled example and you judge? On highpass filters the difference is very easy to understand.

Out of curiousity, I already did though (otherwise I fear that I maybe can't get to sleep this night). Here are three examples. At least one is the mystery and at least one is the corrected Q. The third example is either one of both. You can clearly find the false sheep here:

http://www.savioursofsoul.de/Christian/ ... high-H.wav
http://www.savioursofsoul.de/Christian/ ... high-R.wav
http://www.savioursofsoul.de/Christian/ ... high-S.wav

Christian

P.S.: I've changed the length (cut start/end) to make it hard to be influenced by other properties.
P.S.S.: Please don't post your thoughts too early, only a "I got it" or it can be clearly determined is enough. Then everyone can see, if he hears the difference as well.


*** Edit ***
Just to add some comment here:
- I think that it's still not only the phase difference here. Also the volume and non-linearities may cause the difference (I don't know much about the mystery EQ, but at least the volume of those examples differ slightly).
- I only tried to fit the frequency response and nothing else, anyway the phase changes as well of course...

Very interesting. Well done on matching the files frequencies and amplitude. It's now really hard to "cheat" while listening (that is, listening to the frequency shape only). However, I still think that the broken transients (especially the hihat) is clearly hearable. I'll PM you my answer (which might be completely wrong of course! ).

I suggest you guys download the ABX software to first determine the differences. It's a great learning tool too.

I think this nearly apples to apples comparison makes it clear that frequency, amplitude and shape go a quite long way in emulating nearly anything. Unfortunately there are a few more points to consider like phase and "purity/distortion". The original "mystery eq" in this clip is a relatively clean EQ that doesn't mess with phase too much (unlike the sweep example which messes with phase very much).

Cheers!
bManic

[Zaphod (giancarlo)]

Could you rename them please? I can't download wav files here...

[Christian Budde]

Here are all as a zip file: http://www.savioursofsoul.de/Christian/all.zip

P.S.: Just some more comments:
The magnitude difference is about +-0.2dB, the phase difference about +-7° and the so called "transient smearing" about -60dB (comparing the original with the corrected Q). Although it's far harder to hear, at least two persons were right with his guess.

[Zaphod (giancarlo)]

thanks, wait tomorrow for the pm, I'm going away just now
fancy thread

[Kingston]

I don't agree here: The definition for minimum phase (see http://en.wikipedia.org/wiki/Minimum_phase) also equals the fact that they have minimum group delay = zero latency

In that case the term minimum phase seem to have been used by marketing people in a wrong context.

[Kingston]

Kingston, what i don't understand: you say that more phase shift preserves transients better. How can that be? Any phase shift causes a distortion of impulses, since the different frequencies building up the impulse, are shifted against each other. What you tell me, doesn't fit into the whole signal-theory i learned and therefore i still don't understand, why the system with the higher phase-shift, this MysteryEQ preserves the transients better, while the phase-minimum WavelabQ system smears them.

Don't ask my why more phase shift *seems* to preserve transients better. Yes indeed in light of theory it sounds wrong, because awfully many researchers seem to think any distortion is automatically bad. But in this I case I fear we are diving knee deep into psychoacoustics, and *perceived* transient sharpness.

I doubt anyone knows the correct answer here. AFAIK those pultecs and co. were designed by listening tests, and not leaning too hard on theory. Many designers seem to rely entirely on analytical data and seem to forget that ears do not necessarily work the same, no matter what the scope or data tells them.

As soon as we get more developers thinking in terms of practical sound, with no unnecessary theoretical data to show "because it's right", we'll possibly witness the next bigger leap in EQ quality.

[Barbarossa]

What's the ABX software?

[defjamm]

What's the ABX software?

anybody has a link to a good one?

[defjamm]

As soon as we get more developers thinking in terms of practical sound, with no unnecessary theoretical data to show "because it's right", we'll possibly witness the next bigger leap in EQ quality.

i don't agree. theoretical data is the reason for a certain sound. if it's artificial you have to program it first.
if you have a and you want to copy it with b, you have to analyze it...seems nobody cared until now when i look at that eliosound thread...so many eqs and nobody bothered to deliver something that is closer to the original.

where i agree with you is the tuning of the parameters. this is something analog eqs are often miles ahead. you can get very fast a musical result(which you can match pretty close with a digital eq but it needs way more time). if you meant that i'm with you. but the problem with that is, that dsp engineers are better with math than with their ears. you need guys with a lot of experience to select and fine-tune settings.

[Kingston]

but the problem with that is, that dsp engineers are better with math than with their ears. you need guys with a lot of experience to select and fine-tune settings.

indeed. even in this thread there have been comments proving this, ie. "it fights agaist my knowledge of signal theory". "phase shift causes distortion=bad"...

so what if it sounds good. and hey, they spent 40 years trying to remove distortion and hiss from tapes. Now people are dying to get it all back.

[John Vulich]

The thing is, I don't have any idea how these actually sound, and I don't know how to judge them.

Then I wouldn't worry about then.