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Virtualized snake oil. Cool...
Yes, it certainly falls short of anything we could call definitive, but less so than most subjective reviews of these products where the person(s) reviewing them have no controls at all, just beliefs.
For all its shortcomings, the findings do have a basis in audio science unless someone is able to explain why a $2000 DAC should sound better, without resorting to myths and psuedoscience.
Consistent with my own beliefs, the authors have not concluded that these products should be avoided as they do have many benefits around functionallity, convenience, features and looks. Rather, if the purpose is solely for high fidelity output there is little reason to invest more cash these days over modern codecs that come standard with PC motherboards.
Fools and their money and all that.
I was surprised when noticed that this area of audio industry so much relaxed regarding official specs! Even the output power isn't specified sometimes, or specified at THD 10% that's really cheap cheat )) The same thing regarding the THD+N, I never see any conditions for that, only the number. In audio-amps area I always have to specify the THD+N and the power where it was measured, usually, it is 1/2 of max power, where is max power = power when THD+N reached 1%. If that power is not specified, it is cheating again because a vendor may found the particular power level where is THD+N is minimal. Sometimes I saw vendors simply copy/paste specs from parts used in that product. If somebody did see that nice recourse https://www.audiosciencereview.com/forum/index.php?reviews/ check this out, how often real measurements mismatch vs claimed specs ))
The simple reality is that vendors who sell products are mostly free to post whatever specifications they like, in whatever form they like, as long as there is no legally-provable "intent to mislead or defraud". Note that we have many laws concerning "truth in advertising" and "accuracy of product claims" - however, in most cases, they are based on product safety and liability. (For example, medicines and foods are most tightly regulated, because they have the greatest chance of causing harm if they are misrepresented.)
About the only specific legal regulations regarding how audio equipment is described occur in the original "FTC Requirements for Power Amplifier Specifications" document published at or about 1972 by the US Federal Trade Commission (who regulates interstate commerce of retail products). Recognizing that misrepresentation was very common in amplifier power measurements, and partly in response to lobbying from several "reputable audio companies", the Federal Trade Commission published a legal requirement for how the power rating on home audio amplifiers MUST be both measured and described in advertisements. This is the "standard" that is often referenced - and which refers to things like specifying power as "watts RMS continuous", including THD in the measurement, and providing a specific "pre-conditioning warmup period". Note that this paper is very limited, applies almost entirely to only "stereo audio equipment" (it's applicability to "multi-channel gear", "car audio equipment", and "pro audio gear" is extremely limited), and has been revised several times.
The reality is that, in most cases, the manufacturer is free to provide whatever specifications they prefer, in whatever form they prefer, as long as they don't "intentionally outright lie".
It's also worth noting that there are very few specifications that are actually "universally agreed upon" for audio gear.
For example, you may consider 10% THD to be totally unacceptable for an audiophile quality home audio amplifier, but it may be quiet acceptable for a stadium public address system, or for a low cost table radio or portable music player. Therefore, it's not unreasonable to suggest that it's up to the consumer to decide what specifications THEY consider to be important, and to simply refuse to purchase products whose manufacturers fail to provide those specs.
You also need to realize that published specifications are intended to sell products... usually to specific markets...
So, for example, let's say I had an amplifier that produced 72 watts at 0.01% THD, 92 watts at 0.1% THD, and 102 watts at 10% THD.
(These would be typical measurements for a medium-sized solid state amplifier.)
If I was attempting to market that amplifier to audiophiles, who strongly favor very low THD numbers...
I would probably rate it conservatively at "65 watts at 0.01% THD".
However, if I was marketing it to typical consumers, and one of my main competitors had a similar model rated at "75 watts @ 0.1%"...
I would rate mine as "90 watts at 0.1%" to emphasize the fact that it was more powerful than my competitor's product at the same rated distortion.
And, if I was selling it as an amplifier to be used with public address equipment in small theaters...
I might rate it as "a 100 watt public address amplifier" - and only mention that rating was at 10% in the proverbial fine print.
(Note that, for PA equipment, 10% THD is considered perfectly acceptable, but maximum available volume is important, and "100" is a nice round number.)
Note that NONE of those rating is incorrect, misleading, or "bad" - they just provide the information in the form preferred by the "target market".
So, the conclusion is?
I'm not sure there is any conclusion to be had...
You can't really claim that anybody is cheating simply because they fail to provide the specs that you find useful - because there are no "official specs"...
Each manufacturer simply publishes the specs that they believe will impress the people they hope will buy their product.
And, yes, if they fail to meet the specs they claim, under the exact conditions they specify, then it might be reasonable to say they're misleading you.
However, if the manufacturer simply fails to provide complete information, you can't say they're "cheating" simply because you made incorrect assumptions.
(So, for example, if they describe it as "a 100 watt amplifier", but don't specify the THD, then it's your fault if you assume they measured it at 0.1% THD, but they used 10% THD.)
The conclusion that there is no conclusion to be had is demonstrably, inherently and deductively false because the conclusion that there is no conclusion to be had is a conclusion itself. There must be a conclusion other than that there is no conclusion to be had.
I do the conclusion that smart users choose with reviewers help(like z-reviews, forums like this one etc), most advanced users probably will try the product in offline shops(that's become an exotic way nowadays) or analyze deep in-tech reviews from www.audiosciencereview.com. To other users price and color is enough )) BTW, for an ideal case, which should be quite close to any linear amp clipping behavior, THD 1% vs 10% makes +23% up power rating. Power amps is a much more challenging task vs HPA due to higher currents, voltages and powers(about 1000 times) involved. DAC and HPA area is really trivial technically, any cheating attempts there can show us just shamefully low engineering level.
This reply sooo reminds me of former secretary of defense Donald Rumsfeld's famous "known unknowns" response at a press conference some years ago! lol
"You can't know anything because you can't know everything." --A. Internet Genius
For me the biggest scam are fuses... And power cords costing more than few hundred bucks
Pardon my ignorance, but, what does FTFY mean?