Metrum Octave Dac - What are the Chips used

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nope, thats note going to be good enough really, but will still be interesting.
For the level of distortion that I expect to result, I think is gonna be just all right :)

CD was born with 44.1kHz and 16 bit because that was the state of the art of storage back then. It was a compromise good enough for Anno Domini 1980. There is no point in obsessing about that 44.1kHz, it's just a transport stream for data.
The designers of the CD recognized right away the limitations and used 4x OS to feed the DAC's.
I might not be smart enough, but I think that the engineers from Philips and Sony, that created the CD, where smart enough and wouldn't go for OS if it was that bad and NOS was better. After all they where in competition...
Claiming that all those engineers are retarded and deaf and that you know better than them how a DAC should be fed is just... childish. More like a show-off attitude.
 
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@Ken Newton
I knew before I auditioned the Octave that NOS + no analogue filter doesn't measure well according to traditional views on DA-conversion, but it's probably what intrigued me the most. From the first time I read Kusunoki's article, I've always had a feeling that his views made sense and that those measurements don't actually tell much about perceived sound quality. Last Saturday, after hearing the Octave, those views were confirmed, for me.
One thing, though, the non-fatiguing character of NOS DACs wasn't something that struck me during auditioning, but that might have been the result of listening to an unfamiliar (but very good!) setup.

@qusp, SoNic_real_one
I'm willing to make some basic measurements with my PC-DSO and post them here. Resolution will be limited, though, but as has been mentioned, NOS distortion should be high enough show up just fine.
 
@Ken Newton
One thing, though, the non-fatiguing character of NOS DACs wasn't something that struck me during auditioning, but that might have been the result of listening to an unfamiliar (but very good!) setup.

The fatiguing aspect of CD can be quite subtle - at first. Usually, I'm not aware of it for the first few tracks. When I begin listening to a CD via a typical brickwall digital filter, it usually sounds very clean and very upfront or forward to me. Nothing immediately strikes me as awry. After awhile, usually less than a full CD, I typically begin experiencing one of two feelings. Either I begin to become disinterested in the music, or I begin to feel increasingly anxious or uneasy. Again, the effect is quite subtle at first, but builds. The end result of either feeling is that I become fatigued with the listening session. Conversely, I feel more relaxed or at ease as soon as the music stops. The fatiguing effect is usually more quickly revealed via music featuring massed brass or volins. Indeed, among the most egregious failures of CD digital is the congested and irritating sound often exhibited by massed brass and violins. NOS, at least, as I experienced it via the AD1865 based DAC I built greatly ameliorates this effect, to my ears.
 
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I'm willing to make some basic measurements with my PC-DSO and post them here. Resolution will be limited, though, but as has been mentioned, NOS distortion should be high enough show up just fine.
That would be great. I did post some measurements in the tread from my signature for 991kHz (at -3dB and -60dB) and for 19+20kHz at -1dB (16bit/44.1kHz files generated with Arta). I am really not in to modding back my TDA1541 to NOS... didn't have the performant sound card back when I did have it NOS to grab some measurements.
 
The designers of the CD recognized right away the limitations and used 4x OS to feed the DAC's.

Nope, Sony as co-designer of CD designed its first CD player as NOS - it had a single DAC running at 2X OS but shared between L and R channels. Of course since it was designed by engineers following the theory, it had a fairly steep analog reconstruction filter beyond the DAC.

I might not be smart enough, but I think that the engineers from Philips and Sony, that created the CD, where smart enough and wouldn't go for OS if it was that bad and NOS was better.

You presume too much. Remember Philips came up with 1-bit 'Bitstream' - but then abandoned it. That history falsifies your hypothesis - they didn't listen really.

After all they where in competition...
Claiming that all those engineers are retarded and deaf and that you know better than them how a DAC should be fed is just... childish. More like a show-off attitude.

False dichotomy.
 
That's the point I was trying to make before. You can argue scientific, technical/engineering reason backed up by industry standards till the cows come home, it doesn't matter. The subjectivist will always turn around and say 'but it sounds better'. There is nothing you can do to argue with that and why should you? They are happy with their choice and you are happy with yours.
 
That's the point I was trying to make before. You can argue scientific, technical/engineering reason backed up by industry standards till the cows come home, it doesn't matter. The subjectivist will always turn around and say 'but it sounds better'. There is nothing you can do to argue with that and why should you? They are happy with their choice and you are happy with yours.

yep, engineering science/math/measurements are only used when its a convenient 'truth' and then and only then its given all the weight of a proven fact, often taken out of context so as to present only the parts wanted. if it doesnt gel with their viewpoint the research/science is flawed and not up to the job, we dont listen with instruments afterall... its the same with the parts, the engineers are competent enough to design the parts, but when it comes to using them properly they dont have a clue.

I agree there is little to be gained in this argument because the views are not reconcilable and nor should we deny them their (somewhat flawed) nirvana. but as has been said, its when we are told we must be deaf or stupid if we dont agree that it gets infuriating. Often the line is that worse is actually better, or more transparent/true to source somehow and there is magic vapor trails in the audio relating to 'fatigue' that are masked by the added resolution......because its the wrong kind (unholy?) of resolution I guess..... this information somehow alludes measurement, when the looking glass is turned on it, it vanishes.
 
the above is a bit harsh; I do not suggest that all in this thread are in this group (though some are) and i do not reject your reality but i think you have to find a way to demonstrate these effects before you can call anyone who doesnt believe deaf. I do not think we know it all just yet; thus im interested in Jitter's results.
 
...but as has been said, its when we are told we must be deaf or stupid if we dont agree that it gets infuriating. Often the line is that worse is actually better, or more transparent/true to source somehow and there is magic vapor trails in the audio relating to 'fatigue' that are masked by the added resolution......because its the wrong kind (unholy?) of resolution I guess..... this information somehow alludes measurement, when the looking glass is turned on it, it vanishes.

No more infuriating than when so-called objectivists suggest that anyone who prefers the sound of some component which doesn't measure well in traditional parameters is either delusional or a liar. I took a poke at Sonic becuase he had just been poking at my positive observations regarding NOS, essentially saying that those positive observations must be faulty. He provided no explanation for why they would be faulty, it was more of an assumption of fault, becuase, according to "theory", CD is nigh perfect. You see, while subjectivists ask, do you hear what I hear, objectivists declare, well, you don't actually hear anything because present technical understanding says you don't.

I believe that we've discussed these same issues before, and seem no closer to a common understanding or perspective. My position has been, and remains that, eventually, objective measurements and subjective perception will fully correlate. I believe that if something consistantly sounds different, then the signal must also, somehow, be physically different. I don't believe in audio magic.

So, when will we know that such a full correlation between measurement and perception has been achieved? It will be when our measurements can consistently predict our hearing perceptions, and our hearing perceptions can consistantly predict our measurements. Which, of course, implies that currently, either we are not measuring all relevant parameters, or not measuring them in the right context, or don't fully understand which combination and interaction of measurable paramemters are determinative for subjective perception, and to what degree.

If you don't experience fatigue or any of the other listening flaws of brickwall filtered CD mentioned by those who hear merit in NOS, then consider yourself fortunate. However, because you, or Sonic, may not be sensitive to such flaws doesn't dictate that no one else can be. Sonic is essentially saying that, if it measures good it must necessarily sound good, and anyone who claims to hear anything to the contrary is either a charlatan, or delusional, or simply an ignorant fool. How offensive is that!?
 
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Sonic is essentially saying that, if it measures good it must necessarily sound good, and anyone who claims to hear anything to the contrary is either a charlatan, or delusional, or simply an ignorant fool. How offensive is that!?

Nope. What I say is "If measures BAD it sounds BAD".

You double negate that and presented like a flaw to serve your agenda. Logic doesn't work like that, commtative laws are clear about that. Negating a false afirmation (double negation) does not make it true.
Now, I didn't call any names but sice you brough it up:
- Not knowing that basic facts makes you ignorant.
- Knowing that facts, but still presenting it twisted to serve you agenda, makes you a charlatan.
- Ignoring the bad measurements and the science theory build by hundreds of mathematicians and enginners behid this issue makes you delusional.

You pick what you want. Those are not insults if they describe the truth. Telling me that I cannot fly is not an insult because... it is true.
 
The measure of light as perceived by the human eye is the "lumen" (bear with me, please). This measure takes into account the varying sensitivity of the human eye to different wavelengths. A sensor may see an equal amount of light at (e.g.) 475 nm as it would at 555 nm. Yet, the human eye is far more sensitive to 555 nm than 475 nm and sees the former about 10 times brighter. Lux meters are calibrated for this phenomenon.

The human hearing exhibits similar variations in the hearing threshold, being most sensitive from ca. 500-5000 Hz and far less towards both ends of the 20 Hz - 20 kHz spectrum.
And then there is the masking effect of sound that elevates the hearing threshold significantly. Lossy compression was developed with this in mind.

No doubt NOS filterless DACs measure really bad, but that rubbish is buried under the (elevated) hearing threshold. It's there alright, but it's not perceived by our hearing.
IMHO, it's a correction factor for this that's seems to be missing from audio measurements and that might explain why there is no consensus among audio enthusiasts about the merit of audio measurements.
 
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Well, of course it all depends of what "BAD" measurement means.I can understand that for some peole sound quality is not important, I see them all day with the iPods in the ears.

But that doesn't change the fact that you cannot reverse that logical sentence by double negating it. And you cannot say "if I don't care how it sounds, you all are deaf if you care".
 
You see, while subjectivists ask, do you hear what I hear, objectivists declare, well, you don't actually hear anything because present technical understanding says you don't.

Who's to say that the objectivist is wrong? The trouble is that setting up an experiment, that is statistically relevant, to prove it, one way or another, is so troublesome/difficult that it never really happens. Until that happens I think it is fair to say that the objectivist is right. Why? Because the odds are already stacked in his favour.

I believe that if something consistantly sounds different, then the signal must also, somehow, be physically different. I don't believe in audio magic.

I agree with this 100%. If something actually sounds different and this isn't an imagined difference, then it will be measurable.

My position has been, and remains that, eventually, objective measurements and subjective perception will fully correlate.

Here is where I disagree and not because we are unable to measure whatever this 'magic' might be. I think we are currently able to measure everything that needs to be measured. The trouble, as I said before, is that human preference cannot be measured, it is personal. Just like one pianist will prefer the sound of one piano, another pianist will prefer the sound of another.

So, when will we know that such a full correlation between measurement and perception has been achieved? It will be when our measurements can consistently predict our hearing perceptions, and our hearing perceptions can consistantly predict our measurements. Which, of course, implies that currently, either we are not measuring all relevant parameters, or not measuring them in the right context, or don't fully understand which combination and interaction of measurable paramemters are determinative for subjective perception, and to what degree.

We already know what sounds good. What we cannot do is predict that last few % of 'sound quality' that is determined by someone's personal notion of what perfect sound is.


Sonic is essentially saying that, if it measures good it must necessarily sound good

Yes and it probably does sound good and I don't think anyone would say otherwise. It's just that something that measures worse might sound better to some people.
 
Nope. What I say is "If measures BAD it sounds BAD".

You double negate that and presented like a flaw to serve your agenda. Logic doesn't work like that, commtative laws are clear about that. Negating a false afirmation (double negation) does not make it true.
Now, I didn't call any names but sice you brough it up:
- Not knowing that basic facts makes you ignorant.
- Knowing that facts, but still presenting it twisted to serve you agenda, makes you a charlatan.
- Ignoring the bad measurements and the science theory build by hundreds of mathematicians and enginners behid this issue makes you delusional.

You pick what you want. Those are not insults if they describe the truth. Telling me that I cannot fly is not an insult because... it is true.

Ah, yes. Thank you, for confirming the hostle attitudes I'd suggested you held. So, the gloves are off, are they? Okay.

You say that you disagree with my take on your argument as being; if it measures good, then it must sound good? Fine, lets insert your own description of your argument and see if it then is any less offensive. "Sonic is essentially saying that, if it measures bad it must necessarily sound bad, and anyone who claims to hear anything to the contrary is either a charlatan, or delusional, or simply an ignorant fool. How offensive is that!?" Nope, it's still just as offensive. Your ridiculous red herring protestation about false affirmation is obviously just that, a ridiculous red herring.

You are quick to attack anyone who suggests that, just maybe, a spectrum analyzer doesn't tell everything that's relevant for musical enjoyment, after which, you are just as quick to jump up on a cross (implying that you're being persecuted for the sake of all the professional engineers community) when challenged on your attacks. This tactic is revealing and distasteful.

You have displayed a technical ignorance ranging from the advanced - such as how ASRC actually works, to the basic - such as the fact that push-pull operation cancels even order distortion. I've actually grown tired and bored of correcting your many technical misunderstandings. I mean, do you really want to toss around accusations of ignorance with your rather inglorious record of technical misunderstanding?

You wrote: "Knowing that facts, but still presenting it twisted to serve you agenda, makes you a charlatan. "Ascribing to someone else that what is true about yourself is called, projection. Although, to be fair, perhaps you simply don't know the facts. Which, I could believe.

You wrote: "Ignoring the bad measurements and the science theory build by hundreds of mathematicians and enginners behid this issue makes you delusional. "Associating your own rigid and myopic thinking and mental framing with the creative accomplishments of those vastly more talented technologists, is yet another attempt at a red herring, not to mention, laughable.

There, that cleared the air. We've said quite enough to each other for now, I should think.
 
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Who's to say that the objectivist is wrong? The trouble is that setting up an experiment, that is statistically relevant, to prove it, one way or another, is so troublesome/difficult that it never really happens. Until that happens I think it is fair to say that the objectivist is right. Why? Because the odds are already stacked in his favour.

I would suggest that although it might seem fair to declare that objectivists right, this isn't an acceptable substitute for the truth. It seems that the proper course would be not to assume anything until proof, one way or the other, is established. As you may have heard said before, absense of evidence isn't evidence of absense.

Here is where I disagree and not because we are unable to measure whatever this 'magic' might be. I think we are currently able to measure everything that needs to be measured. The trouble, as I said before, is that human preference cannot be measured, it is personal. Just like one pianist will prefer the sound of one piano, another pianist will prefer the sound of another.

Able to measure, and actually measuring are two different things. For example, we were able to measure TIM distortion before Matti Otala, but we didn't realize the need to measure it until after him. However, what I didn't originally make clear is that I meant for a single given listener, not between different listeners. So, for example, if a single given listener consistantly hears differences between interconnect cables, or power cords, or what have you, then there is some physical difference in the signal at some point in his system. That difference is likely real, and not merely audio magic. Of course, psychology can play a role, which is the basis for most of the objections by the objectivists, I should think.

We already know what sounds good. What we cannot do is predict that last few % of 'sound quality' that is determined by someone's personal notion of what perfect sound is.

I think that the raging debate bewenen those who hear very significant differnces between NOS and digital sinc filtering, not to mention vinyl (or solid-state versus thermionics, for that matter) sort of belies the notion that we all agree or know what constitutes good sound.

Yes and it probably does sound good and I don't think anyone would say otherwise. It's just that something that measures worse might sound better to some people.

Probably sounds good? Perhaps. Necessarily sounds good (a rhetorical point, I do realize that you aren't suggesting that)? Not in my experience. I do gree that there is a partial correlation between good measurements and good sound. But the lack of full correlation seems to lead us directly to the observed truth that we are either still not measuring some relevant parameters, or we are not properly assessing the context for the measurements we are already taking. :cool:
 
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I would suggest that although it might seem fair to declare that objectivists right, this isn't an acceptable substitute for the truth. It seems that the proper course would be not to assume anything until proof, one way or the other, is established. As you may have heard said before, absense of evidence isn't evidence of absense.

Maybe not, but in the absence of a double blind test (which represents the case most of the time), to see if the subjectivist really can hear a difference (such as in a cable), we've got the objective point of view that says there is no apparent difference. This again is up to the individual to decide. Given no double blind test and only the measurements on said cable, do you believe the subjectivist is actually able to tell the difference, or are the measurements to be believed instead? I would choose to believe the measurements as being far more credible then someones ears. After all the measurements have been proven correct for pretty much all other aspects of science and scientific development, why should this be any different?

Of course, psychology can play a role, which is the basis for most of the objections by the objectivists, I should think.

Absolutely and this is the major issue here. I will not believe that someone is capable of hearing the differences between one cable and the next without a double blind test showing them capable, or measurements, that in turn, show that the two cables present enough of a difference in their properties as to make them detectable by ear.


I think that the raging debate bewenen those who hear very significant differnces between NOS and digital sinc filtering, not to mention vinyl (or solid-state versus thermionics, for that matter) sort of belies the notion that we all agree or know what constitutes good sound.

What I meant by this is that we know what constitutes good sound in an overall sense. A lack of gross distortion, a lack of compression (ie no clipping or otherwise), a flat frequency response from 20-20k and maybe a couple of other key but simple/essential parameters.

One could take the system designed by the engineer and by definition it would sound good. It might not sound 'the best' to any individual person, but the overall reproduction quality would be good.

No doubt you could take that system and then tune it from 'good' to 'excellent' for any of the given people in their listening rooms, but this last notch in performance is the icing on the cake or the last few %.

The trouble we get to with audiophiles is that they take this by all accounts 'good' and turn it into 'unlistenable' because it isn't their idea of 'excellent'. Then, anyone who disagrees with their idea of excellent is then, by their definition, deaf. Coincidentally I don't really mind being called deaf.


Probably sounds good? Perhaps. Necessarily sounds good (a rhetorical point, I do realize that you aren't suggesting that)? Not in my experience.

This is my point exactly. Good by what measure? I'd argue that the good measuring piece of equipment will sound pretty darned good, but it might not be your specific idea of what is 'best' and this I would say is down to your own personal preferences.


I do gree that there is a partial correlation between good measurements and good sound. But the lack of full correlation seems to lead us directly to the observed truth that we are either still not measuring some relevant parameters, or we are not properly assessing the context for the measurements we are already taking. :cool:

Maybe the problem is that what we really need are strict double blind tests at every opportunity, to actually see if you are really hearing something as being 'better' or are you in fact just imagining it. I believe that by far the biggest influence (and possibly the only important influence) is the human mind. My mind is capable of having me perceive my system one day as amazing, yet on another day with exactly the same music I'll be totally unimpressed. The system in this time didn't change, my state of mind however, did.

Another aspect worth thinking about though is the idea of perfect sound. Is this actually = to the original being reproduced in the most untouched, uncoloured way? I think it's very reasonable to assume that we could in fact prefer a sound that is somewhat exaggerated and a bit larger then life. In other aspects we might actually prefer a sound that has been toned down considerably in some way. Maybe the original is somewhat piercing to the ears, but the harmonic/melodic content of the music is inherently beautiful. Is it wrong to twist the original through a DSP to make the beautiful melody listenable? Someone else might prefer it the way that it was. I have a friend who cannot stand listening to operatic sopranos because they 'hurt' his ears. Obviously there isn't anything wrong with the singing, neither really is there anything wrong with his ears, he just can't tolerate the way it sounds.
 
I have inherent problems with double blind tests as typically conceived and implemented for audio tests - serial random changes - as I don't believe they adequately test the pattern learning and recognition processes we use when we listen to and hear music. They don't allow the subject to control the processes of familiarisation. They don't necessarily test the context of the change that matches the pattern recognition processes of the subject. And often the results for subject averages are then used to 'prove' that that is the limit of discrimination for all individuals - on average, test subjects were unable to discriminate between A and B therefore A and B are below the level of discrimination (for all subjects).

If we used the same double blind processes for testing the limits of visual discrimination - serial random changes - we'd long ago have concluded that the our visual capabilities were far inferior than they actually are.

I'm sure many of us have seen one of those 'candid camera' videos where a guest goes up to a hotel reception desk and while they are checking in, the assistant bends down behind the counter. When the assistant stands up again it is a different person. Yet the guest doesn't spot this 'serial blind test' and carries on. On the basis of this test the subject is incapable of recognising the difference between two human beings, yet it is the context of the test that determines the subject's limit of discrimination, and it is the subject's ability to control familiarisation which will determine their level of discrimination. Similar examples could be given about identity parades, or the detail (or lack of it) that we take in when we drive, but time between seeing the original and the identity parade, and the circumstances of viewing the original and the identity parade will determine the ability to discriminate. With visual comparisons we can always present samples side by side and allow the subject to spend as much time as they wish in examination and deliberation. Memory is not involved. With audio comparison we always have to present the samples consecutively. Memory is always involved.

My daughter has friends who are twins. I've known them since they were babies and now can immediately recognise and identify them. But for many years I could never separately identify them. If I saw them serially - one after the other - then I would always have failed to identify them; in any serial double blind test I would have failed to discriminate between them. Side by side they were always obviously different.

Familiarity is important. I know the minutiae of my wife's face inside out. I know when she is ill, troubled, stressed, tired, has changed make up, has a changed complexion, even if the change is only to a minor degree. I certainly can't do that with acquaintances; I might be able to do it with particular friends. Not possible with strangers.

I do think it is possible to define constructive and useful double blind test conditions that do fairly test our limits of audibility, but I don't believe the typical ABX test configuration will do that.
 
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Obviously the nature of the test is important but one thing to bear in mind is we only tend to try and remember things when it is important. When introduced to people who I will never see again I always tend to forget their name 10 seconds after I was originally told, simply because I've got other more important things on my mind. We wouldn't tell that the receptionist had changed simply because we're not paying any attention to it, if we knew to then things would be different. Of course if when you walked in you noticed that the receptionist was the most beautiful person you'd ever seen, then yeah, you'd notice if they suddenly changed into someone else, either that or you'd be very confused.

The thing with the audio test is that the person being tested should be given full control over the test. As in they can listen and switch between A and B as many times as they like at the start so they are able to try and spot differences and make a mental note of which they think each is. Heck they could even write down what they think the differences are so as not to forget which is which whilst doing the test. Then they are played back sound samples with A and B randomly swapped, where they have to identify which is which.

There is another way to look at this though, if the difference is so small that it takes a lot of familiarisation for anyone to think that they are aware of when whatever it is has changed, then arguably there is no difference. Of course you would bring in the argument about your wife and those twins, but the two are perhaps not quite the same thing. In the case of your wife and the twins you will slowly pick up on little idiosyncrasies that you wouldn't necessarily notice with only a small amount of exposure. Some of these things might be glaringly obvious, like the receptionist change, but due to the way that we perceive things it takes a while for us to actually notice them. Once noticed though then they are extremely obvious, like you might tell the twins apart because one has an extra freckle on their left cheek, you always forget how many freckles there are, but when the twins are together you can easily count them and be able to pick out which is which. This isn't now a small difference, it's a neon sign in a pitch black shopping mall and you will never get it wrong.

The thing with audio and things like this is that we have a terrible memory of how things sound. Lets say you were able to correctly identify A vs B by some sort of 'tick' or 'sign' that you picked up on during your first listening session. A and B. You heard for instance that on sibilants, A made it sound softer then B and you were able to identify this correctly. The next day you go back and try the same thing and A has been replaced with something that now sounds more sibilant then B. You are asked this time to please identify which one is A and boom, you say B and you've got it wrong.

Technically speaking you weren't able to remember which A was, only the tiny difference from between the two. Initially you were able to tell the difference, but I would argue that during that time you weren't actually listening to music, you were trying to find some sort of 'tick' that would let you know which was which.

Perhaps a better test in this case would be musical enjoyment. The trouble with the human mind is that when confronted with a situation like that we will always try and find tell tale signs of when A or B is playing etc and for an audiophile it will turn into trying to listen out for certain things and when we do that we're not actually listening to music, we're trying to listen to a piece of equipment. This is excellent if we're simply trying to prove if we can hear a difference between A and B, but it's next to useless if we're then asked, which one do we prefer. Well A sounded slightly softer round the sibiliants, B wasn't sibilant sounding though, they were both good, hmm do I want A or B in my system, maybe A will sound too soft in the long run blah blah blah etc.

Maybe a better test would be done from day to day. Day one you listen to say five of your favourite tracks on system A. Then the next day you listen to the same five tracks on system B. On the second day you're asked which one you preferred day one or day two. You then do the same thing 10 times over with A and B randomly swapping their position and you then see if you consistently preferred one or the other. If you didn't then surely either of them would give you the same long term enjoyment.

I mean in terms of deciding whether or not I subjectively prefer the NOS DAC this thead is about, or something of technical perfection by DCS. I would first want to do a direct A/B comparison to see if I could actually tell them apart. This in itself would be interesting, but regardless of if I could or couldn't I would want to do the day to day test. In an A/B comparison you are unlikely to notice any gross listening 'fatigue' effects as these tend to catch up on you, but the day to day tests should pick on this, if it exists.

I mean perhaps you can compare this to computer monitors. You've got two side by side and when asked to compare them you say, sure yes, the one on the right is A and the one on the left is B. It's obvious, A is considerably brighter and more punchy looking then B. When asked which do you prefer you pick A. On a longer audition though you find that A is actually too bright and hurts your eyes, you should have picked B. Just being able to tell them apart isn't enough.

In a similar way you're asked to tell A and B apart and this time you cannot, both look identical, one works at a different refresh rate though, you decide that you want A. You take it home and after a few hours your eyes start to hurt and you get a headache, you don't know why, but you swap it for B, which is visually identical, but the headache goes away.

In both cases simply being able to tell the two apart wasn't enough, nor was it important in being able to tell which one you prefer. Here of course there was a perceptible difference and a good technical explanation as to why you preferred one over the other.
 
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