Sunday, November 29, 2015

NOSDAC: Cult or Cure ?

It was a very nice audio listening session.  The first ever where I'd invited audiophiles from the audio society to enter my main listening room and hear the magic.  All were favorably impressed, more or less, it seemed.  (You can never axiomatically interpret something like this, as if the system is Really Bad, you may not get any bad comments either.  It may only be where people actually feel threatened as you're nearing the pearly gates, but differently, and that can't be right.  So as they say among academics, the smaller the differences the greater the arguments.)

So from the most sage, the actual engineer with decades of professional experience actually making recordings, I got mostly (and actually somewhat surprising) approval.  What I had feared getting gored, the panel-to-subwoofer mating, as just got a not-so-quick touch-up days earlier, was pretty much accepted as successful.  But it was the panel sourced highs that got the barb.  "Harsh" or something like that was the word.  Despite all the praise, "I couldn't live with it" was the emphasis, which seemed out of place among all the other comments.

OK, I conceded.  I have indeed been aware of it and always struggle with it.  I deal with it mostly by moving my head into or out of the very central beam of the electrostatics.  You have to be sufficiently forward of the central beam of the electrostatics to get the smoothest highs, otherwise it sounds brittle.  Others later testified to what I described.  This near field speaker issue is real and needs further investigation.  I strongly believe this is the primary source of harshness in my system.  Later listeners confirmed the improvement from having head forward of the beam, and the criticality of this.

I didn't mention, but it may be clear to readers of this online diary, that much of my effort of the past 4 years has gone to addressing the harshness issue.  I recently bemoaned my trek in this direction as a loss to the then-alleged more important work of getting the bass decent.  But then I did some bass decency work just-in-time for the listening party.  But the kinds of things I've done were exactly replacing the Behringer DCX outputs, which aren't much praised by anyone (though objectophiles might say they were perfectly fine, having distortions well below audibility) with using a DEQ to drive an external DAC, currently the Audio GD DAC 19 which had inspired the engineer himself to obtain and now use the Audio GD Master 7.  Along with that change, the gain structure of my whole system changed, and now I run very close to 0dB with no attenuation, digital or otherwise, to compromise the resolution.  (I previously often ran with attenuation around 20dB, and despite my defending this with the claim that I have 24 bit resolution, I know it was suboptimal.)  So I've made major changes that I think can be defended on multiple objective grounds in attempts to eliminate the harshness, and they've been greatly beneficial.  Also, just using the Krell amplifier as compared to others I have, has a huge positive effect.

But my most sagacious guest had other ideas and didn't seem much interested in exploring the speaker/listener alignment possibilities during the listening session itself (though in much later comments, after the lamp had mysteriously become broken after someone tried to turn the lights off, he mentioned that speaker and listener orientation would be on the top of his list if I let him fine tune my system for a week).

Instead, he stepped into the measurements vs listening morass, and singled out the Krell amplifier as a potential part of the problem, effectively because of focus on achieving good measurements, and how many have moved to SET amplifiers, despite horrible measurements.

I look at the Krell FPB 300 as something very different from an amplifier designed to get "good measurements."  The very way it works is something very special in my view, with the output stage operating without loop feedback.  I believe this design is ideally suited for large electrostatics because it rejects electrical back EMF from the speaker, decoupling that from the actual amplification.

An amplifier designed simply to get "good measurements" could be made and used at far less cost than the Krell.

I have long experience with the Krell and a few other amplifiers, mostly the Aragon 8008 BB another very fine amplifier, I believe.  What amazes me is how much better the Krell sounds, and I believe this is precisely because of the special design of the Krell FPB, which isn't found on most other amplifiers, even Class A amplifiers, even most Krell amplifiers.  When I read about FPB amplifiers, the 300 and the 600, I just knew they were the ticket for electrostatic speakers which require vast VA swings, but accept vast EMF back from the speaker without compromising the signal integrity.  And everything in my experience has confirmed this.  They are the magic ticket for Acoustats anyway.  Now this is my experience, and my technical understanding, even if not acceptable to objectophiles.

Simply claiming that one might like the Krell because of good measurements demeaning.  That doesn't do justice to my sense about the Krell.  Actually, I suspect in a number of ways the Krell isn't the best measuring, and maybe not as good measuring as I would like.  If the amplifier has had to thermal limit down to the second stage of Class A operation, which is common, then peaks much above 100W are going to be increasingly distorted.  It is possible to get measurably significant distortion out of a Krell if one knows about how it works and can give it the right tests to show its weaknesses.

WRT SET's, I've never heard one that I liked, and have especially noted harsh sounding SETs at audio shows, sometimes besides very sweet sounding push pull tube amps.  There is every reason to believe that the high measured distortion is real and ultimately can do no good as it inter modulates with itself.  Many if not nearly all PhD audio scientists kind reject them (as do ALL contest for them...and amplifier with 10% distortion cannot possibly be virtuous, and there is certainly no measurable advantage in distortion at low levels, as might be claimed).  Most of my long time audiophile associates reject them too.

Would I call SET a cult?  Yes, although remarkably widespread.  The audio science behind SET is remarkably thin but the sound is preferred by many thousands of listeners.  I think in most cases the deficiencies only become overwhelming at loud levels because of the companion cult to super-high-efficiency speakers.  In this case we are not talking so much about claimed-to-be audible differences. SET's sound different, no question about that, can be easily distinguished from low distortion amplifiers once the SET's are operating with levels of distortion well above 1%.  You may well claim there is a difference, though, in SET Superiority.  SET cultists, of course, believe in the SET Superiority, which comes from the virtue of simplicity.  They can "hear" that among all the other qualities and limitations of real SET amplifiers, which they may admit to.  Yes it's harsh when cranked up, but played softly it has intimacy or whatever.

And along a similar vein, the sagacious advice was that I must try (and would likely love) the No Oversampling (NOS?  didn't that mean New Old Stock or do we just distinguish these things on context?) option of my Audio GD DAC.

My mind waffles about whether I should even try this.  If I call SET a Cult, then beyond any question NOSDAC is a Cult.  It's far smaller group of people who use this kind of DAC (though interestingly, a group that highly overlaps SET and especially openness-to-SET as could be assessed by including those who formerly-used-SET), the backing among objectophiles and PhD audio scientists equally or even more thin, etc.

Strangely, then, one advantage that NOSDAC has is a more technically defensible argument, one that can be shown With Measurements (ironically).  NOSDAC's preserve the timing information.   They are technically perfect with regards to timing.  You can just look at the oscilloscope photos.  All the pre-ringing, post-ringing, and similar effects go away.  Now, finally, what you see "looks" exactly like, or the closest visible approximation to, the signal going in.  (Apparently the timing aspect is a key part of the visible picture.)

The problem is that technically perfect timing is obscured by enormous mass of audible distortion.  Unlike SET's which may be sufficiently undistorted at low levels to actually suit many people by objectophile standards, NOSDAC's distort horribly at every amplitude level, in every way, etc.  It turns out those apparently small "visible" differences are actually huge, we don't judge amplitude distortion well on visible graphs of square waves.

And what do I mean horrible?  Like, say, 30% THD.

That number 30% I am taking from PeterSt, Netherlands based senior member of ComputerAudiophile, in this long threat started by NOSDAC'ers   He seems knowledgeable and respected.  He was once a NOSDAC owner, started to investigate how it worked, began to realize it was a horror, then devised his own minimum phase DAC based on 16x oversampling.

The ever reliable Archimago has an exploration of NOSDAC's with actual graphs from a forward thinking DAC by TEAC with multiple options, one of them being NOSDAC.

I might point out that many cult (and otherwise) respectable DAC designers, such as King Wa at Audio GD, prefer their own default oversampling settings.  That's where he put a lot of his intellectual energy, into getting right as-close-as-possible digital interpolation and filtering.  He also wants to show you what he has achieved by giving you the other options as well.  And it seems like many try the settings and end right back at King Wa's default.

Not to say that there aren't NOSDAC designers, in which category I would include Audio Note, who love their NOSDAC's.  This category has many cult famous companies, Metrum comes to mind, but by far Audio Note is the largest.  But of DAC designers overall, these are a tiny proportion.  In fact NOSDAC designers are what you might call anti-designers.  They "design" the oversampling by simply not including it.  And usually (following Audio Note) not including the filter either.  That's it, design over.  You don't have to be a very technical designer to be like that.  You don't have to have a PhD or even know math or audio science or anything at all.  You simply have to have a lot of Chutzpah, and if you know anything about the subject generally, combined with intense contrarianism.  But what if you had, one day, tried making a NOSDAC, and, voila, it sounded good by Listening?

So here we are back to the sagacious question: Listening vs Measurements.  Though perhaps my dislike for this drafting of the dichotomy comes from many particular issues with measurement per se.  By definition, a set of measurements cannot be complete, it's only a set.  There are infinite possible measurements, performed in infinitely many ways, as well as facing infinite inherent measuring limitations.  In audio, measurements have been fantastically exaggerated (such as Instantaneous Peak Power, occurring the moment the unit instantaneously self-destructs with man-made lightning), specified with incredible accuracy, or rounded up to nice numbers just to look like you don't care.  The best audio measurements usually come expressed by graphs rather than numbers, and the output of RAA is very nice, but still far from complete, and what manufacturer has given anything like the output of RAA?

You see the word Listening is being used here as if it The Ultimate Answer (because in a way, it must be), and Measurement as the thing we know which is often somewhat incomplete or misleading (and we have loads of other experiences with that in our expending enterprises), in a way to color this as if you must be a fool not to do what the questioner begs: "listen for yourself."

With a similar misdirection, I could redraft the question as Guessing vs Sound Engineering Principles.

While a seemingly simple argument can be made for the notion that you should just "listen for yourself" (and be fooled too, I would add) there are many fundamental problems with it as a tool of audio design and/or selection.  To wit:

1) Potentially biased (most likely, I would say, without thorough DBT)
2) Subject to future change (including the very next time)

Because of 1 and 2, the results of any one listening test have to be held in complete contempt, as not even having enough wrongness to be wrong, without either additional thorough testing (pref DBT), or reasonable objective story to back them up.

Further, the big problem with bias is that it feeds on itself.  Once you have developed the bias, it then becomes part of a very powerful bias to stick with it.

Now until researching this post I hadn't realized that NOSDAC's have a duller sound with proportionately less high frequencies.  I had known they produce more distortion, from aliasing, but had wrongly figured that distortion to add to HF making the sound brighter.  Instead what happens is the audible distortion is in the form of products which appear throughout the audio band giving it a kind of richness, not brightness per se.

So now that I know this, I could use the duller highs of a NOSDAC to balance out what may be the excessive brightness of the Acoustats.  I'm not sure if it would work like that, but it might seem to help in this way.  I'm tempted to try this simply for this reason.

But crucially any such "help" is truly a band-aid.  It wouldn't fix the underlying problem(s) whatever they are, just by adding a companion kind of distortion to cover up the original problem.

Certainly a better approach would be that rather than covering up problems, they should be sought out, and engineered out directly.

Of all the band-aid approaches, using something like NOSDAC to cancel out problems is the worst approach.  It's generally adding heaps of distortion, unrelated to the original signal altogether.  It's far worse than other band-aid approaches like using EQ to ameliorate room nodes.  Of course EQ isn't solving the actual problem (which is reflections in a bounded space), but it is using a linear means (which isn't itself non-linear distortion, nor produce more additional downstream non-linear products) to cancel out a major linear chunk of the original problem, and it is doing that directly by directly addressing the actual room mode frequencies.

Probably my NOSDAC loving friend would agree that NOSDAC's shouldn't be used as a palliative either, but rather that the problem is made to sound worse by being layered with the time distortions caused by oversampling.  If NOSDAC works as advocates claim, it should be used with the best systems as well as the worst, making the best systems even better.

And at this point, we can imagine a world of existing audio systems, many sounding fantastically good, and almost all of them, probably 99% or higher, NOT using NOSDAC's.  Ordinary OSDACs must be pretty good if they are used in most of the best audio systems.

Unless all the OS DAC designers, virtually all academic audio scientists, and most system designers are wrong, there is not really any need to even try NOSDACs.  For most people, this is simply a waste of time.  There isn't enough evidence to think this is a worthwhile change.  Everyone doesn't need to try everything for themselves, especially when the results of listening tests done improperly, as most are, can be confounding and create superstitions.

If we did want to verify NOSDAC claims of the importance of audible distortions, we could devise a number of possible blind tests.  One is a simple bypass test.

I haven't done this test, but I find it very hard to believe that the NOSDAC path would sound more like the original overall than the OSDAC.  In my imagination, the NOSDAC sounds somewhat different, whereas the OSDAC sounds about the same.  This would conform to the most important (if imperfect) set of tests done on digital audio by Meyer and Moran.  Listeners could not reliably hear the effect of digital encoding and decoding added to an audio path, even when done ten times.

The only way this imaginary bypass test could be claimed as a win by NOSDAC folks would be the claim that it maintains something special, amidst all the other clearly audible differences, a claim that would not be very credible.

While what one does with audio reproduction for personal enjoyment is a personal matter, I continue to believe that listeners are best served by the most accurate reproduction.  Harry Pearson called such a thing The Absolute Sound, and I believe in that, though not perhaps in his methods for gauging and approaching it.

Accurate reproduction is the goal of virtually all of the audio press, the audio engineering establishment, academic audio scientists, and so on.

There is a major dispute between subjectophiles and objectophiles, or black hats and white hats in Peter Aczel's terminology (himself being a self described white hat, John Atkinson being a self described grey hat) on the essential methods of achieving accurate reproduction.

Sighted listening tests are the standard of subjectophiles, double blind tests and in some cases just measurements are the methodologies of objectophiles, with subjectophiles often claiming measurements are unimportant.

My belief is not in measurements, which are incomplete and tentative, but in principles, when you can find them.  And the question doesn't come down to listening or not but to something more fundamental: how do you assess truth?

Is it really necessary to tour Auschwitz to know that the holocaust happened?  I think not, and in fact some denialists have toured such places only to bolster their opinions.

Truth in our experience comes not so much from direct observation as received wisdom.  In most cases, it isn't necessary to go beyond that.

Exploring the edges, where contrarians lurk, can be an honorable activity, but it is not something everyone need do.

Now this is not to say that in all our interactions with people and objects we are constantly assessing truth in various ways.  But most of these assessments are based on thinking and reasoning about known (or presumed) facts.  Not on direct observations.

Even our direct observations aren't really observations.  As much as science knows about perception, it knows it to be a largely constructive process, that builds models, often first, then tests them against the experience, or constructs them based on a perceived reaction to experience.

So there is actually no "need" to do listening tests at all.  It is generally a good idea to do listening tests on speakers, but largely I have purchased most of the speakers I own on pure speculation, without an opportunity to pre-listen (and such pre-listening tests, as at dealers, I'm not sure how much validity I would attach to, the best testing is always in-home testing, which is also the most difficult and most rare).  And I think I've done pretty well, with the Revel M20's, Acoustat 1+1's, and Gallo A'Diva's I own.  The speakers I have in my now unused pile wasn't all that bad either.  Given that I've been in this game for 47 years, it's not surprising I have a large collection of what I might now consider mistakes, though I'd try to rationalize them as stepping stones.

One merely needs to find the experts, or the ideas, one actually believes in.  Most of this is not a process of direct observation, it is a process of reasoning.  At best it is a measuring of other's consistencies.  At worst it is an assessment of other's tribe.  I fear I may not be doing the best always.

But that's ultimately what it comes down to.  I believe generally in what the majority of academic audio scientists believe, roughly the mainstream of the editorial staff of the Journal of the Audio Engineering Society, who won't accept subjective testing only double blind in most cases.

That means, I'm likely to find little or no merit in NOSDAC's.  Even if they initially sound pleasant, or uniquely satisfied, I'd still rationalize that as a euphonic quality I'd ultimately get tired of.

I believe if ultimately NOSDAC's actually are the way to go (which is entirely contrary to the way things look now), eventually this will be discovered, and pretty much everyone will switch to them.  There is no essential need for me to be on the cutting edge of such new things.  Not if I don't want to. Not if I think it's going to be useless.

Ultimately I don't think it's worth doing most audio listening tests.  There are infinitely many subjectophile "tweaks" one could try to make better sound.  There are endless cables one could try, and cable stands, cable separators, and on and on.  There's no respectable evidence (JAES is the standard, or the objectophiles at Hydrogen Audio) that such things make any difference.  As such, the best that could be reasonably believed about them is that they make small improvements.  How many small improvements does one need to bother with?

Exactly none by some accounts.  All by others.  I apply a little attention to everything, with more hoping to focus on the most important than doing so.  I excuse myself: this is my playtime, I'm just trying to have fun, and the important work has more difficult and boring parts.  And realistically there are indeed problems with exploring the most important kind of changes (or perfections!): loudspeakers.

One should always go after the biggest possible improvements, or at least the low hanging fruit.  In almost all audio systems, that means the loudspeakers (and the room, EQ, absorbers, etc).  Very little attention need be paid to the electronics and uncompressed digital sources because they are already very highly perfected.  And I do hew to that at least some of the time.  I pretty much ignore audiophile tweaks except as fashion accessories--I like them for that.

If loudspeakers are the biggest factor, as objectophiles and I believe, loudspeakers should be what almost all of our tests are about.

But what about the recording engineer?  It is commonplace that even experts aren't experts about anything in their own precise field, let alone others.  It seems to me he has keener observation about many things than most, but that does not prove his all his observations, ideas, or beliefs are correct when I find others with ideas I find more believable.

Given what I am, I can't simply accept any expert's opinion exactly.  And I believe that even many people with good powers of observation and refined expertise can still be profoundly wrong about some if not many things.

So I decide which ideas of which experts to accept, and which to reject.

How do I do this?  Mostly by my own reason.  Very little based on my own observations, but I have performed DBT's on myself and others, and that experience continuously shapes my ideas.  Most subjectivists haven't done such things, no matter how many sighted tests they have performed.  Basically what even the most minimal participation in DBT shows is that hearing is unbelievably biased and unreliable at qualitative testing, and audiophiles can't prove they hear the things they claim to. This is because we've evolved to correlate, to ferret out connections even if we get a lot of false ones, not comparators that can reliably compare things over time, and time is the ether of sound.

Even for audiophiles the ultimate sense isn't hearing, it's thinking, and especially determining what to believe and what is important.  And examining the thinking of others is not a distraction, it may be the best place to start.

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