Digitalt ljud är perfekt! (Nåja, nästan)
unfortunately I haven't had much time to participate in this thread, but this is related to a LOT of what I have been doing for the last several years, some of which have made it into products you all know about.
I have a little bit of time right now so I'll go into a broad overview of what I have found in my wanderings through digital audio.
There are at least three issues with USB that need to be addressed, it is rare for all three to be dealt with well in the same system, making it possible to do this is what I have spending a lot of time on.
The three things are:
Timing should be familiar to everybody on this thread. Its is the age old issue of where the clock that feeds the DAC comes from. Early implementations were terrible, having to sync a local oscillator to the USB signal. Asynchronous mode fixed that, allowed a local oscillator in the DAC to be in charge. Unfortunately MANY implementations did this very poorly so the advantage of async was not realized fully. Fortunately things are MUCH better today, with many manufacturers finally realizing how to do this.
Everyone thought this would BE IT, the ultimate interface. Unfortunately it was not so, there were OTHER things involved here.
The first I started looking at was signal integrity of the USB bus. Exactly how this makes it through to sound coming out of the DAC is not fully known at this point. BUT it does look like increasing the signal integrity at the DAC USB chip decreases small noise voltages in the ground plane of the DAC. Devices such as the REGEN are designed to increase the signal integrity going into the DAC USB chip.
Some manufacturers have added isolation techniques after the USB chip, trying to block the ground plane noises from getting to the clock and DAC chips. Again unfortunately many of these implementations have not been done very well. But even the ones that ARE done well still do not seem to completely get rid of cable and source dependencies. There still has to be something else.
Enter leakage loops.
I don't have time here to go into detail on leakage loops, I have written extensively about this in recent posts. A few important points. This is caused by leakage from the AC line through capacitances in the power supply to the DC output of the supply. They have NOTHING to do with the traditional "ground loops" that happen through the safety ground (third pin) of the AC wiring, it is something different. Earthing (ground rods etc) have nothing to do with this. Leakage loops always go through at least two power supplies: AC line, PS A, DC output to circuit A, interconnect to other box, DC of circuit B to PS B back to AC line.
Leakage loops depend on the type and implementation of both power supplies. Leakage current is line frequency (50/60Hz) plus harmonics, plus any crud from the PS. It is primarily low frequency AC, but higher frequencies can exist. The problem from the leakage loop is the voltage noise generated when the leakage current flows through a non-zero impedance, such as the shield on an interconnect between boxes (analog or digital).
ALL AC mains connected power supplies have leakage currents, SMPS seem to have considerably more leakage current than most LPS. These leakage loops have always been there in audio systems (except the very earliest ones that ran off batteries!), but computers in audio have exacerbated the issue considerably due to most computer systems running exclusively from SMPS. Thus many of the ills of digital audio have actually come from the leakage current of the SMPS rather than the "noise" of the digital systems themselves.
There are two ways to deal with the noise: block the loop or decrease the impedance of the loop. Blocking the loop means blocking the flow of the leakage current anywhere in the loop. There are several ways to do this, a battery supplying a component prevents leakage current from an AC powered supply. Breaking the ground of an interconnect with say an optical interface breaks the loop. But beware of this, the "receiving" end of the optical interface requires power, if that comes from an AC line connected PS, you are adding in another leakage loop. It may be better than the original, but it will still be there.
The LPS-1 and the Intona deal with these two sides of loop breaking, the LPS-1 at the PS side and the Intona at the digital interconnect side.
The OTHER way to deal with leakage loop noise is by decreasing the impedance of the loop. One interesting way to do this is on the AC mains side of things. Remember this IS part of the loop. Many audiophile have special "power conditioning" devices designed to "lower noise on the AC line". Unfortunately the implementation of these devices can greatly INCRESE impedance between devices plugged into them! They do decrease the noise between neutral and hot, but increase the impedance between devices, thus increasing the noise generated by leakage loops. My experience has been that in many cases the leakage loop noise increase wreaks more havoc than any advantage from decreased neutral to hot noise.
Thus my recommendation is to get rid of the expensive filters and instead use a simple power strip that has nothing between outlets other than thick wire. EVERYTHING goes into this strip. This will dramatically decrease leakage loop noise simply by decreasing the impedance on the AC mains side of the loop.
So in order to get the best from USB you need an async implementation done right, good signal integrity at the DAC and some means of blocking the leakage currents from the computer's power supply from getting into the rest of the system. It takes all three to really get the best from USB.
Note there was nothing in here about "the noise from all that digital stuff going over the wire to the DAC". My research seems to show that this doesn't happen very much, the leakage current from the power supply is FAR more important to great sound.
Now that we have covered USB, lets briefly touch on Ethernet. It seems like the same things affect SQ. You still need the main timing control to be in the DAC, signal integrity matters and leakage currents are very important.
Fortunately Ethernet is inherently galvanically isolated if you are using UTP. BUT if you are using STP (shielded) with connectors that connect the shield you are right back in the leakage current mess.
At this point in time I am not sure what the passive isolators are doing. They are high frequency transformers which usually have almost no response at the frequencies usually associated with leakage currents. They might be changing signal integrity in a good way, I have never looked at one on a scope so I don't know. One possibility is that the power supplies frequently supplied with network equipment (routers, switches) are some of the worst I have ever seen with some pretty strong high frequency components to their leakage current. These isolators may have better rejection at these frequencies than the ones commonly used in equipment.
The Optical system completely block any leakage current of course, but you can get some back from the power supply feeding the downstream side of the optical system. The signal integrity of the downstream side is also very important and is also usually dependent on the quality of the power feeding it. An LPS-1 will do well for both purposes on the downstream side of the optical system.
BTW the speed of signaling on gigabit Ethernet is much less than high speed USB. Both 100 megabit and 1 gigabit use the SAME rate of 125 mega symbols per second. High speed USB is 480 mega symbols per second. HUH? 100 and 1000 are the same? 1000 uses four pairs at the same time, 100 uses just one pair, AND 100 uses 3 voltage levels (high low and in the middle) but 1000 uses 5 voltage levels. The result is one bit per symbol vs two. So bandwidth of transformers needs to be exactly the same for 100Mb and gigabit, just a lot more of them for gigabit.
I guess that is enough for now, and I didn't even talk about vibration isolation. från tråd https://www.computeraudiophile.com/forums/topic/29206-overall-isolation-network-usb-and-power/?page=12#comment-592269