Things I don‘t know

Let me see if I can answer some of your questions -

1. Polarity - It has to be in software, reversing it in hardware means all your ones become zeros and zeros become ones.  This isn't analog!   Conceivably, a bit stream could be designed for that but to what end?  If it is done in hardware, then it takes some silicon to covert the phase, so SW is usually the way to go.

2. Clocking - 10m?  I am not sure what you mean by 10m.  I believe the question you need to ask is about jitter.

3. Galvanic Isolation - You are correct, galvanic isolation is the way to go.  The problem is, it is relatively expensive.  If they can achieve similar results in SW, then that is the direction they are forced to go.   Note that the same thing applies to balanced inputs and outputs in the analog domain.  Specs love to quote CMRR but it is CMB on the output device that dictates how good the CM rejection is because excellent CMB is much harder to achieve.  Galvanic isolation on the output is really the way to go, yet it is a cost issue, and many, if not most, audiophiles would ignorantly question a transformer in their signal path.

4. Class D - It is still a young and evolving technology, I do believe it is much too soon to expect standardized clock frequencies or power supply topologies.  Designers need to have the flexibility to improve their design as they see fit. 

I’ll have to admit I can’t reliably tell if the polarity is reversed or not, at least not with music. My equipment does allow me to switch the polarity.

&spatialking,

my point on polarity was that it is determinant of sound quality but being ignored by top equipment designers

10mhz is the standard frequenzy for masterclocks controlling several components in the same system, typically by a 50 or 75 Ohm BNC connection. Most top class devices do not provide a connection for this.

Galvanic isolation cannot be replicated in software.

Agreed on class D, however there seems to be no discussion about different approaches so far.

You have to look at this from a market point of view. Do the engineers at Toyota not know how to design a vehicle that rides like a Rolls Royce or a performs like a  Ferrari SF90? Whether they do or not is irrelevant because the market cannot bear millions of those cars on the supply side, so we are forced to compromise to a price point to sell to a wider market. Making more Ferraris would put pressure to lower prices to compete, yet the lower prices would preclude production of those cars.

Same applies to audio. Only a few manufacturers can compete to a very select buyer who demand the best. But sometimes, a Schiit Audio comes along and offers digital players for less than three grand that competes with (or even beats) these kilobuck digital players, but the audiophile community judges them by the price tag. "It sounds good for the money" is usually the dismissive review.

(1) Many listeners can’t hear polarity reversal, even listeners with good systems and musical knowledge. As to why hardware doesn’t always offer it, it’s another feature that costs money to include. Why don’t (most) preamps have tone controls?

(2) The 10 MHz clock, last time I looked, was more designed to enhance long-term stability; at least, that was the view of the digital expert whose essay I read 1-2 yrs ago. The clocks in digital devices are getting better at the more critical issue, short-term stability.

(3) Galvanic isolation is a tool to achieve an end: low noise, distortion, etc. Perhaps manufacturers can achieve that in other ways. Measurements and listening of recent relatively inexpensive DACs (by SMSL and Topping, e.g.) indicate that to be the case. It’s the result that counts, not the means to get there.

(4) See (3). There is more than one way to get the job done. Maybe the ’optimal’ value of those things depends on other factors. Also, manufacturers are always looking for ways to distinguish their equipment, and it’s easy to say "our circuitry is special" and it’s hard to contradict. It makes great ad copy and can be used by reviewers who want to sound knowledgeable ("Audio Idiot explains that their special HAN transistors are faster and widely used in aerospace applications, where absolute accuracy is vital"). Finally, audiophiles show a disturbing tendency, encouraged by some reviewers, to think that anything more complicated, exotic, and expensive is better, so that always generates debate.

Another unfortunate characteristic of audio discussions is what was mentioned above: the tendency to look at the means, rather than the ends. Whether it's "Class A is better than ....", or "The ESS chips are not as good as ..." or "MOSFETS are ...", or "NOS DACs are the only ones that ....," in my view, there is far too much obsession over the mechanics, rather than whether the result sounds like music.