What do audio systems do? At the most basic level, they are Illusion Engines. I'll repeat that: a hi-fi system is really an Illusion Engine, a type of mechanical contrivance that hypnotizes the audience into thinking musicians are somehow present (or at least nearby). If the contrivance fails in this, it fails utterly, just as a magic trick entertains or it doesn't. Re-framed in this context, "accuracy" simply doesn't apply. It's a bit like rating a dream, or a hallucination, on an imaginary "accuracy" scale, although the mainstreamers have come up with a series of incantations, body postures (jaw-dropping, pants-flapping, cojones, etc.) and audiophile-approved test discs that purport to accomplish this feat. Although watching the highly trained Positive Feedback review staff going through the audiophile motions is pretty entertaining, the hi-fi systems that seem to produce the most agitation from them only rarely produce an illusion of musicians for me. From this experience I conclude that different kinds of people enjoy different kinds of magic tricks. Some people like THC, some like psylocybin, some like a dry martini that is shaken not stirred, some like Night Train fortified wine, and others never indulge in any form of self-amusement lest the Wrath of God (or Science, take your pick) smite them down. Having described audio systems as a special class of Illusion Engine, there's one group for whom the word "accuracy" actually conveys meaning: recording and broadcast organizations with ready access to professional musicians. For the last 30 years, BBC monitor speakers have been subjectively assessed by rapidly walking between the control booth and the performing hall. The short trip is a quick reality check, and the BBC and other national broadcasting organizations command the resources to have both large groups of professional musicians and the engineering talent to design high-quality monitoring loudspeakers. This is why I give special weight to the writings of D.E.L. Shorter of the BBC, who pioneered the techniques of modern crossover design, cumulative-decay measurements, and swept distortion measurements as techniques to chase out subjective coloration. The realm of the ordinary magazine reviewer, hi-fi retailer, and consumer (also known as "the food chain") is somewhat different. These folks are technically challenged, and incapable of building or designing their own (unlike the inhabitants of the levels above). They are forced by their limitations to approach audio in a building-block fashion, picking and choosing amps, speakers, cables, CD players, power cords, MPingo blocks, Vibraplanes, etc. They habitually fasten on magic one-dimensional numbers, such as cost, watts, THD, freq response, the F3 bass limit, or if especially clueless, the 2-bit universe of "Stereophile" Class A, B, C, and D ratings, or the 1-bit binary logic of "THX-approved". This may seem a harsh view of the industry, but it is "accurate" in terms of which products sell and which ones don't. Without a 'Pile rating or the "THX" logo, most American retailers won't give a new manufacturer the time of day. Sorry, that's just how it is. So in one sense, "sonic accuracy" is no more than market acceptance of a certain type of sound. By this logic, McDonald's defines accuracy in food, Microsoft in software, and Nike in terms of fashionable third-world apparel. Accuracy = perceived market domination. Viewing the audio chain in terms of convenient marketing "chunks" of CD players, power amps, and speakers, is to cater to the ignorance of the mass market. Test data is simple to measure at this "chunk" size, but correlation to sonics is very low. Correlation to sales pitches aimed at reviewers, though, is excellent. The device level is where things get a lot more interesting for the designer and enthusiast. For one thing, the "chunk" size is about right for getting at least a modest degree of correlation between what you hear and what you measure. For speaker drivers, roughness in the 3D cumulative-decay waterfall is a good index of potential coloration; however, the 3D waterfall loses most of its meaning when applied to the entire speaker, since the crossover neatly hides most of the gremlins from sight (although not from the ear of a skilled listener). The device-level approach also works for electronics; the audiophile-approved 6DJ8/6922 vacuum tubes lose much of its "low-distortion" charm when its abundance of 3rd and higher harmonics appears on the spectrum analyzer. Similarly, the audiophile favorite of the 12AU7 loses some of its luster when a dirt-cheap surplus NOS 6SN7 has three times lower distortion and three times the drive capability. These things *are* audible; when you work at the device level, repeatable correlations between sonics and appropriate measurements begin to appear. Unfortunately, as long as magazine reviewers are incapable of appreciating the functional difference between a mu-follower and a SRPP, they will never penetrate this level of understanding. And neither will their readers. The device level is the arena for the skilled illusionist to work their magic. The adventurous DIY triode enthusiasts, unlike the armchair generals of the mainstream magazines, have actually built mu-followers, SRPP's, RC-coupled circuits, transformer-coupled circuits, and have explored the wonders of parallel feed. Some of the geekier folks have turned on their spectrum analyzers and peered at the little wiggles down in the -80dB region ... and lo and behold, found useful correlations between seeing and hearing. By doing so, they are treading in the footsteps of Norman Crowhust, D.E.L. Shorter, and other pioneers of the Fifties. If I meet Mr. Colloms at the CES, I'll ask him if he's read my article in Vol. 9-4 of Glass Audio, which deals quite explicitly with the matters he reports as mysteries. Crowhurst and Shorter dealt with these issues a good thirty years ago, so I fail to see what the great puzzle is all about. Crowhurst's mathematical derivation of the harmonic multiplication properties of feedback is quite clear, and Shorter's analysis of how IM distortion dominates HD with real-world musical sources is equally clear. Put the two together and it is apparent that conventional feedback circuits create very large numbers of low-level sum-and-difference IM products, which effectively adds a dynamic program-modulated noise floor in addition to the static noise floor. The appropriate protocol for measuring this dynamic noise floor is a full-spectrum noise stimulus with a spectral hole (passively) notched out, then measuring the amount of spectral contamination after it passes through the circuit under test. Repeat for complex loads, and now you start to get a little bit closer to real-world testing conditions. Other tests can measure the wideband noise spectrum of the power supply under dynamic load, the relative contributions of driver and output-stage distortions, the presence of dynamic shifts in transistor betas due to thermal pulses on the die, the interaction between Class AB switching, Nyquist stability with distorted and reactive loads, and settling time, etc. Add in Frank Deutschmann's work on feedback chaos-theory, and we can have quite a party with lots of strange measurements guaranteed to drive any reviewer into fits of hand-waving, jaw-dropping, and pants-flapping. The problem isn't triodes versus transistors, but a gradual dumbing-down of reviewers, dealers, and consumers over the last two decades. Not by accident, this process mirrors the increasing concentration of power towards a single publisher, which has the power to act as a make-or-break gatekeeper for the entire high-end industry. Students of economic history are well versed in this phenomenon, which results in the slowdown or absence of innovation in a given industry once power is concentrated in the monopoly-holder. This is why the American mainstream hi-fi industry is at a technological dead end with declining sales and a gradual erosion into the home-theatre mass-market ... this is the natural result of the expansion of monopoly power against the other stakeholders in the industry. Since the American mainstream manufacturers, reviewers, retailers, and consumers are locked up, innovation and a re-think has to come from outside the closed circle. And it has. Thanks to Glass Audio, Sound Practices, Vacuum Tube Valley, VALVE, Audio Asylum, and of course the one-and-only Joelist, there is now a genuine alternative to the mainstream, and a revival of a serious technical discussion that was almost forgotten 30 to 40 years ago. Accuracy? As New Yorkers like to say, "Forgetaboutit!!!" This word has become just another marketing buzzword, as empty of meaning as "hip" and "cool". In science and engineering, yes, accuracy has a clear meaning. But not in audio. Aloha Audio: http://www.aloha-audio.com Ariel Speaker Page: http://www.teleport.com/~lynno/Ariel.htm   Reprinted with permission.