2. digital
  3. 180276-149317

Things I don‘t know

Digital is very much an emerging transmission form and there are a few questions where I simply don‘t know.

1. In the digital domain it is very easy to shift polarity of recordings and the effects are very audible. Yet few devices offer the capability even in very high end systems. Conversely it seems a standard feature on software for computer based systems. This matters greatly since probably half of all recordings are made out of polarity.

2. In digital accurate clocking is of paramount importance to achieve good leading and trailing edge definition as well as spatial rendition. Yet few Dacs even in high end devices and even fewer streamers or switches offer 10m clock interfaces.

3. Even small RFI/EMI or ground level intrusions are very detrimental to accurate D/A conversion. Yet most Dacs still don‘t provide galvanic isolation on their inputs and often claim to address the issue with error correction in the digital domain. Do designers simply not know better?

4. Recent advances in Class D amplification seem to point the way; yet there seems to be no consensus on optimal sample frequency nor power supply design for these devices.

Finally, while rare exceptions like @atmasphere see their task as clarifying and educating on the issues, the vast majority of designers either don‘t make the effort or just go about shilling their widgets.

While I am sure that this is only the beginning of a list of digital issues worth discussing,the usefulness of Audiogon Fora rests precisely on elaboborating and clarifying on all issues immanent in this new approach to things and in most instances the issues don‘t at all relate to issues discussed purely in the analogue domain.

antigrunge2
mike_in_nc
1,147 posts
 

(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.

invalid
1,180 posts
 

Regarding 10mhz clocks, do you want a square wave or a sine wave?

erik_squires
16,041 posts
 

Everything I've read is that external clocks are worse than a really good internal clock.  The distance in the leads makes them more susceptible to jitter issues than a low phase-noise internal oscillator.

Class D amps are not (as Atmasphere likes to point out) digital.  D was just the next amp type in line.  They are switching amps with analog comparators, but it is often argued that the switching frequency being higher pushes the noise out further.

dynamiclinearity
258 posts
 

Actually there is no sampling frequency for class D because class D is an analog encoding function. It is unfortunate that it's called class D. It was only called class D because it was the next amplifier format and it came after class C(lousy for audio).

Power supply is critical for class D. It must be very fast because class D goes from zero to max theoretically instantly(impossible but the closer it comes the better). That implies lots of current and a very low output impedance for the power supply.

antigrunge2 OP
1,400 posts
 

@erik-squires

that is one line of arguments, indeed. However Innuos spends enormous efforts on reclocking both USB and Ethernet connections and best I know DCM offers full external clock support for all its units. There is also a vibrant market for master clocks from Esoteric, Afterdark, Mutec, Cybershaft, Antelope et al. I‘d argue the jury on clocking is still out. In my case reclocking my dac and Etherregen yielded major benefits.

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