> even mediocre equipment (probably with exception to the speakers) nowadays is able to reach astonishing linearity.

While we have much better cheap amps now than we used to, there's still quite a bit more of noise in the bottom end. You make it sound like $10 of electronics would give great sound (assuming eg: flac audio source, dac and "digital"[1] amplifier). It's not quite that simple. Feeding the whole thing from a battery power source is simple, cheap and can work to reduce the most common/obvious source of noise -- the AC mains (but is only practical for head-phone use).

As for measuring distortion -- it's a little bit like with lossy image codecs: it doesn't really matter what the numbers say, what matters is how we perceive it. In audio-mastering/studio production lossy-ness matters (because if you loose n% of the signal on every iteration, and you do 100s of iterations through the pipeline, the noise crowds out the signal). In testing, it helps guide the development and production (quality assurance).

But in the end, that's just a guide. The trick, is to not buy into the placebo -- while at the same time recognizing a basic fact: the human brain is great at patterns, and filtering out noise. Listen to a badly tuned radio long enough, and you no longer hear the noise. Until someone walks in and adjust it to be on station again.

Listening to really crappy sound (eg: at least two generations old embedded audio from laptops -- not sure about latest generation(s)) -- there'd be a ridiculous amount of noise. Couple it with cheap head-phones with eg, little or no bass -- and listen to music like that for a couple of months -- and you'll be able to convince yourself that that's just fine. Just like if you smeared a thin layer of vaseline on your computer screen and left it on there for months, you'd probably stop actively noticing it was there -- but if you wiped half you would instantly see the difference.

Then compare it to any low-end "hi-fi" set-up, and you'd be surprised how much clearer, and better most things sound. If not, stick with what you like.

It makes absolutely no sense to buy a more expensive setup than what you can tell the difference between. And even if you can buying the best at any price doesn't make sense.

And if you want to sit in a room and really listen to music/soundscapes -- be that classical music, pink floyd, jazz or anything else -- the room is just as important as the gear, as other's have mentioned.

Oh, and if you want to get the most out of your setup - calibration is always good. One reason I prefer stereo is that it is comparatively simple. I'm sure that in theory one could develop a "CalMan"[2] for audio -- given that pretty much every source now is digital, one could probably set up a test track that allowed one to correct for many distortions (created by the system, the speakers, the room...) in real-time.

But I must confess, while I would love to calibrate my monitor to get more correct color -- I'm highly sceptical of the idea of programming my DAC to get "more natural" sound. But that's probably the audioplacebo talking, not the rational mind.

[1] http://en.wikipedia.org/wiki/Class-D_amplifier

[2] http://calman.spectracal.com/store/p71/CalMAN_RGB_with_Spect...