Obviously his delta improvement and mine do not match. Perhaps I measured a stock PM1 and PM2 as baseline, and Alex started with a broken PM2 set. Alex claims in so many words that my rig is broken and his measurements from his super-secret rig and bat-like hearing tells him his cans are uber-netural and worth well over $1k. Any disagreement will yield a "Sorry, you're wrong", "don't understand why", and in so many words, ears in disagreement are not discerning.

   There is one easy way to check if I was in any way cheating with baseline measurements of the original PM-1s. All one has to to do is compare them to my measurement of HD-600 both posted in one graph earlier in this tread. Then simply compare differences between two graphs on my measurement to the differences between PM-1 and HD-600 frequency response displayed on the graphs posted on Inner Fidelity by Tyll.  See how closely those differences match and please stop suggesting I used some broken OPPOs, unless you want to say Tyll was also measuring a unit as broken as mine.
   To finish this endless discussion about "superiority" of my rig and "bat-like" hearing of mine once and for all I suggest we perform one simple experiment. Please send me your HD-600s, I will measure and build a couple of DSP filters based strictly on those measurements, one for each ear. Then we upload one into my processor for both left and right drivers to get a first preset. We will also upload two separate filters for both left and right drivers to get a second preset. Then we can use a bypass mode for the third preset.
   If you are able to hear the difference between first two presets (which I assume won't be more then 0.5db in few places) then you just like few others I already checked this with do have a "bat-like" hearing. We can also compare bypass with DSPd preset and if you agree that my filter sounds better it would suggest that measurements I perform are no BS. If it's all wrong please keep on posting as many evil pictures as you want but if I am right please simply say it. Does this sound reasonable?
   On top of all the above we could possibly set up the same comparo at the upcoming CanJam and a make everyone vote. Random listeners not knowing which preset is which would make this pretty much a blind test and would probably give us a bit more scientific results.
   I never questioned your ability to judge the right sound from wrong and that is why I keep on sending you my units. At the same time I criticized your measurement system before and will do it again simply because I think it has flaws. I also criticized some issues with measurements from Hans as you criticized albeit very politely those from Tyll but that doesn't mean we should all get upset with each other. Instead let's try to hear and understand what everyone has to say, think it over and communicate as a gentleman of fortune. This is what pirates do.
   Either way this turns out I am open to a reasonable critique and suggestions, as always.
ps.
     Thanks a lot for the link about possible flaws in Tyll's measurements, very entertaining. I will have a few things to say about this too but maybe after/if I earn a bit more credibility here.

   The processor is a prototype of a pro grade DSP. Correction algorithms are my own developments and proprietary. Adjustments are being made to align time, phase and frequency response. What one can do with DSP is complicated but at least we have our ears to verify the results, so we can simply do the experiment.
   I honestly believe if something sounds truly right, it will sound right for most if not all. In other words; if something is right it will never sound like shit to anyone. One will never mistake black for white if not completely blind. Once we start adding colors choosing the right combination becomes much more complicated and all of a sudden one ends up dealing with all kinds of tastes for different sound signatures. This is why my goal was to make PMx2 as neutral as possible.
   

   I have a lot to say about all of the above but probably won't have time within the next few days. One thing I want to emphasize on though: the absolutist approach. Every human being has an equalizer built in by the nature which helps us distinguish natural sounds throughout our life. When we get ear infection for example, everything all of a sudden starts to sound off simply because aforementioned equalizer couldn't realign itself so quickly. We all are surrounded by the natural sounds pretty much 100% of the time, even when we are asleep (a human nature survival is based upon this ability).
   What happens when we put headphones on and play the recording? We substitute all the natural sounds for the artificial reality but our survival instinct simply can't be shut down just like that and our built in equalizer can't adjust to a new environment so quickly. Therefore if either recording (at least 90% of the time in my opinion), headphone (90% of the time, again in my opinion), or the upstream gear (maybe 75% of the time) is nonlinear we would feel something is off and get uncomfortable. This applies to each and everyone of us (musicians, audio reviewers, audiophiles or untrained listeners) because we all live within the same ecosystem called Earth and that ecosystem is a setting point for our equalizers from the day we are born. Trained ears though would recognize flaws a bit quicker and with more confidence only not because their survival instinct is stronger but because they are much more familiar with the sound of musical instruments in real life.
   Basically it all boils down to our most important instinct: survival, which simply can't be tricked so easily. Therefore I say if everything sounds right, anyone/everyone will know it pretty much immediately. If it doesn't then something will keep on bugging us pretty much subconsciously no matter how beautiful the music is, artful the recording or how resolving is the gear involved. I say we better start producing realistic recordings and linear gear. 
   Going back to our case, you feel my cans are "not too far off from what I think they should be..." which for me is a very good sign. This  "little bit off" thing could be attributed to either upstream gear (in your case I believe that chance should be pretty slim), recordings (same thing, even though not many are good I suppose you would still know your way around those pretty well) and lastly my cans. Well, suppose some more work may be needed if I wanted to bring the absolute perfection to all and everyone then :-).

Too much emphasis on FR in this thread. Human 'eq' or psychoacoustic adjustment (aka. Brain burn-in) is only one metric of many that produces natural or accurate sound. Personally I think most people are too attuned to their shitty speaker rigs as their personal references rather than actual live human instruments and performances. I think it becomes clear who is who after some discussion with people. Most people don't even know what their own reference tracks actually sound like tbh and are shocked the first time they actually hear it properly.

Look no further than bright and analytical sounding upstream gear versus dark and compressed sounding gear. They can all measure flat beyond 20-20khz and be within thousandths % of distortion. That should tell someone how dominant those two metrics are for accuracy in the grand scheme of things. Important but not really primary if you ask me unless your standards for audio reproduction are fairly low at which point we shouldn't really be talking about totl price tiers. Focus on only FR for anything beyond a couple hundred bucks would just be a red herring to distract from other inadequacies IMO.

Software peq is cheap to do, acoustic mods are more involved, but neither will push a driver beyond its design potential.

That's the truth behind most of the 'reviews' one sees on HF and most elsewhere.
Peoples 'reference' is completely screwed over by a wrong 'calibration', this may not be the case for people dealing with real instruments though.

personally I agree with AZ that a flat FR is paramount for correct tonal balance and that this sounds correct to me as well... on WELL MADE recordings that is.
It could sound  on a lot of other recordings.
I also agree with the statement that a flat FR isn't everything there is to it.

There will never be such a thing as a 'universal' and correct sounding headphone that will be liked universally.
It's a good thing to strive for 'perfect' reproduction though and a select few people may like it.

Perhaps.... you (AZ) should not stare at Oppos ONLY though as the FR roll-off is audible (as far as I can tell) and seems a limitation of the driver as is the distortion in a certain frequency range. There is only so much one can do with mechanical/acoustical/electrical mods indeed.

For instance the roll-off that is seen in all the plots and which UB metioned is not solvable with acoustic mods but may be improved upon with EQ only.
So you can 'passively' modify the Oppos as much as you want but most likely will never be able to 'repair' the roll-off.
That is from my POV as I have NO experience with any Oppo at all.

Just my opinion of course...

   
   I did some testing lately and gathered very interesting and promising results. General public was given a listen to two in my opinion of the most linear, neutral sounding headphones I know of. Many of the recipients had some kind of degree in music and played different instruments in their past, many but not all. All have listened to the same song with the same volume aligned for both sets and could repeat the test as many times as they wanted. None were audiophiles and none were familiar with neither of the headphone sets.
   So far the vast majority preferred the same one set of headphones to the other one ( 10 out of 11 recipients to be precise). Two of those people preferred the other set initially but changed their mind in the end. No comments of any kind were given by me during the testing.
   I will surely continue this experiment as I found results to be very surprising and the whole process very entertaining. At least one major thing became clearer to me already as a result; general public does not seem to be biased by the typical sound signatures we all are aware audiophiles have come to accept. I also found the results to go pretty well along the lines with my theory on our survival instinct.
   As for the roll off and how this basic signature and distortion figures can't be changed, please see the graphs of my other pair of PM-1s measured earlier by UB and supposedly on the same rig.

Alex sent me his modified Oppo PM-1 cans. Thanks mang

I do not have the stock PM-1s with me anymore, but at the meet I thought the modded PM-1s had a little more bass than what I'm hearing right now. Who knows, maybe I'm a b ass head or something. Anyway, to me the impact is perhaps lessened (even from the stock if my memory serves me), but it's not gone. If anything, these are a little more laid back in the bass region. The treble is pretty good. I think the treble on this is an improvement over the stock. More airy. It is a bit brighter though.

I dig these. They sound perhaps a little less low-fi to me. Note I did not dislike the PM-1s in their stock form, but didn't go crazy about them either.

These seem also a little heavier than the previous ones I heard (perhaps due to the mods). Still, pretty comfy though, and not as heavy as some other orthos.

Here are some measurements...

Frequency Response



Distortion Right



Distortion Left



CSD Right



CSD Left



Impedance