How far can EQ really go towards truly equalizing headphones? - Page 7

I tend to agree with what LFF said, and with udauda's references (btw thanks): Weird phase would likely mess with how everything sounds (sound quality) in mono or stereo... and in particular with stereo, probably will mess directional cues in some weird ways to. How much... I don't know.

 

For mono in particular, and in headphones, since left and right play the same thing, the result would be the absence of directional cues ... and "plant mono firmly in the middle of" our noggin 

Edited by ultrabike - 6/13/12 at 11:29pm

 

I don't think those were phase issues, but FR (more correctly magnitude response) issues, since phase is "determined" by it.

 

 

From that audioholics page:

 

(Emphasis by me.)

 

Additionally, they used all-pass filters that cause huge phase shifts. Not something that would happen in a single driver headphone.

 

If the system (headphone) is minimum phase then there is a unique relationship between the FR magnitude and it's FR phase!

 

Thanks xnor!

 

If headphones are indeed minimum phase in real life, I can see why that's a good thing (in so many ways: reversible, unique FR phase and mag relationship, transient time duration...)

 

As far as phase or magnitude issues affecting the sound quality... well I sort of see a chicken and egg dilemma there given their unique relationship ... You can't really affect the phase without affecting the magnitude and keep the system minimum phase... unless in those studies somehow they set the overall system to non-minimum phase? Anyway, I'm very happy with what I got from this: I can get phase out of the magnitude FR.

Edited by ultrabike - 6/14/12 at 5:52pm

Note that while there is a very close relationship between frequency response magnitude and phase, if you go back a few posts(http://www.head-fi.org/t/612665/how-far-can-eq-really-go-towards-truly-equalizing-headphones/75#post_8455577), it is evident that looking at the whole picture (phase and magnitude as opposed to just magnitude) is important to determine how the output signal is going to behave!

 

Now: How far can eq really go toward truly equalizing headphones?

If the headphone is well behaved: relatively time invariant (positional invariant here might be a challenge though), very linear, and minimum phase... Well pretty darn far. Make a filter with poles and zeros where the headphone's transfer function (z-transform) has zeros and poles respectively and you might get a flat line (where the headphone can reproduce signal of course - best not to equalize close to perfect notches there for SNR considerations). Furthermore, cascade a second filter to tailor things to your liking... Not saying all this is super easy though. Note there are positional variations in response, THD, SNR issues... Just, I can see EQ can help to a good degree to the best of my knowledge.

Edited by ultrabike - 6/14/12 at 6:09pm

According to Lip****z & Cabot, it is evident the phase issue is more distinguishable with headphones for sure. And take a good look at the other two articles too.

Are there any headphones that actually have a serious problem with phase, or are we talking purely in theory?

We are talking about equalizing headphones, and the phase issue that may be associated with it. 

 

No it's just the nature of the butterworth filter that tries to "stay" as flat as possible in the passband, i.e. trades flattness in the magnitude response for a greater phase delay. Take a look at the gain and group delay plots on wikipedia and compare butterworth with bessel.

It's that sudden and steep change in the magnitude response that causes a peak in the phase delay. Like both of us have said before, the phase response can be reconstructed from the magnitude response alone.

 

 

I agree.

Headphones aren't that far apart in response. It wouldn't take a lot to EQ any headphone into sounding like any other. I can't imagine that causing phase problems.

The only headphone (with measurements available) that I think could have problems with phase is the DT 48 E, but the magnitude response is a much, much greater problem and there's no question about the audibility. ;)

 

There are some limitations though. One can not expect to fully EQ apple ear buds into LCD-2s or HE-400s with their deep and relatively clean lows. Some of the biggest offenders are deep notches and early roll off at ether side of the spectrum which can be challenging to fix.

Well, you certainly can't make a silk purse from a sow's ear, but I bet you can make a pretty fine apple out of an orange.

LOL
 

I think you are not interpreting these papers correctly. First of all, the author does not say what headphones were used. This makes it very difficult to draw accurate conclusions. For all we know, he was simulating one $20 headphone with another $20 headphone. Somehow, I doubt they were transmuting iBuds into Stax 009s :-) Second of all, if you look at figure 6 on p. 258 of the second article, you will see that the match was far from perfect. The best headphone sounded better when representing itself than when being simulated by another headphone.

I am curious enough to write the author and ask him which headphones were used, but not right now, maybe later today or tomorrow.

Another point to keep in mind is that the authors only used one minute of jazz as a test track; this would not be enough variety of music to fully test the headphones. Indeed, the piece used (Glenn Miller, "In The Mood") does not have much deep bass, which might be one of the most difficult parts of the frequency range to equalize -- it would be more subject to distortion.