It is very hard to describe in words aural phenomenon, which is one reason why reviewers are constantly seeking better (and often more hyperbolic) adjectives. "Mid-Fi" and "high end" are gross labels that don’t tell us much: in the era of late 60s to early 70s you might more easily characterize a mid-fi system as one which consisted of a receiver, a pair of bookshelf type speakers and a modest turntable, compared to separate preamp, basic power amp and turntable that allowed the installation of a separate arm (often made by a different company). These days, some lower cost hi-fi equipment sounds worlds better than its equivalent from 50 years ago-- solid state is much better sounding, to my ears, than it was in the early ’70s.
It’s very hard to predict what a given set up will sound like in the abstract, leaving aside listener preferences. There’s the room to consider, and how the equipment is set up within a given space with its acoustic characteristics. Some of this is science and some is art. If I had to describe what a "high end" system would sound like in the abstract, compared to something lesser (and this isn’t necessarily measured by price or brand name) it would be: a more natural "flow" to the music without sounding "reproduced" or "played at you,"; a slowing down of the proceedings--which may be partly psychological, where there is more "space" between the instruments, both in terms of timing and physical placement in the presentation; front to back "depth" as well as the harmonic decay "envelope" (from attack to the gradual diminishment of overtones that linger and fade) and an ability to "decode" information in a way that isn’t analytical or clinical sounding, but makes your brain "work less" to imagine the illusion of a real performance. If you know what a real instrument sounds like, say, the piano, you need a recording that has effectively captured it (not easy in my experience) to hear what a good system can do in reproducing it effectively, from the "growl" of the lower registers to the sparkle and ethereal quality of the upper notes and the harmonics that can linger as each new note is struck.
Each of us has an imagined "ideal" for good sound. I’ve heard a lot of systems, big and small, in homes and studios, over the course of more than five decades. Some of the big expensive systems fail and other more modest equipment just "gels" in the room, producing a convincing illusion. Part of this too is that you are evaluating a "system," not just a series of components.
When I got serious about this hobby in the early ’70s- the Quad loudspeaker combined with tubes and a good turntable was eerie. It has considerable limitations in terms of bandwidth, dynamics and the ability to play "loud." But it is still a reference for midrange, which is where most of the action is. (I have a vintage system set up that replicates what I was running in the mid-70s that is based on the Quad Loudspeaker).
By contrast, my main system can play louder, deeper, has a similar "see through" midrange and does not suffer from the some of the limitations of the vintage system. Yet both are musical and very natural sounding.
I had an industry person here a year ago who wanted to listen to some test pressings of a sound track and kept asking me to "turn it up." He was listening for nits-- although my main system is more revealing than the vintage one (the latter being somewhat forgiving), neither system is "forensic" in its sound. He would have been far better off in a studio with big JBLs being driven by a lot of power (I use single ended triodes), to hear these pressings as if under a microscope. That’s not what I’m chasing; instead, it is about a quality of realism of instruments in the room.
Since I have two dedicated rooms here, the problem is largely one of space and scale. There is only so much I can crank the big system before it overloads the room. Thus, I cannot produce the scale of a large orchestra in a 2,800 seat auditorium, though I can produce a very convincing illusion of one in my room, given its size (roughly 31 x 14, narrowing like a horn mouth toward the front wall).
The real measure of this is going to be your ears and your listening experience. Get seat time; hear some top systems and what is possible. Work from there as a reference point, recognizing that sonic memory is a tricky thing.
