but again, I'm talking blu-ray disks which have a ton of video data, far more then audio data, and there was no visible degradation on a 70" display set to 2160 resolution. I just don't see how the video could be perfect, while the audio is distorted, doesn't make much sense. ... All I can do is tell you my experience, and my experience says that interference,and/or powersupply problems whether it's rf or what, IS audible in a digital stream. No matter what source file, whether audio only or a film with audio, and no matter which piece of software I used to play said file the same distortion/noise was heard without variance. Also, no matter which soundcard I use, either fully balanced using TRS 1/4" cables, tos-link, usb, hdmi, or rca.
Once i fully inserted the upc cord. noise gone. never to return, so far. You had to put your ear nearly up to the tweeter/midrange to even notice the distortion, which is why I suppose I didn't notice it until I installed new speakers and was listening to ensure each driver (three Emits, three Emims each speaker) were working properly.
OK. I'm sitting here thinking, and IIRC, even when the media was paused, the noise was audible, but how would this noise be able to make it through the dac, and fully balanced connections?
If the noise was audible even with the media paused, that proves it wasn't in the digital chain.
Though the technical impossibilities should, in principle, be proof enough. The technical impossibility is on the order of electrical interference affecting the flow of water in your garden hose, or spraying the garden hose on an (insulated!) outdoor power cord and having it affect the electric lawnmower powered by the cord.
Of course, those are analogies. A more relevant example would be electrical interference changing the text of this message. In a working error-correcting digital system, that can't happen. Indeed, the long, complex chain of digital interconnections from my laptop keyboard to your screen has been practically hammered with electrical interference. The rough distance between us is (according to Google) 5,110 miles, which means an even greater distance of electrical and optical cabling plus dozens of electrical interference producing and absorbing devices.
Despite that, I'm sure the text I've typed here is
exactly the text you see there.
Though we're talking about forum post text, audio data is no different. Digital networks, whether local like a home network or wide-area like the Internet, don't distinguish data representing text in a forum message from data representing an analog audio waveform; it's all just packets of data to be sent here and there.
Whether for sound or text, the reason we use digital transmission is
because it is so impervious to analog interference, no matter the distance travelled and level of electrical noise encountered, up to the point where the interference becomes so bad that it breaks the network and then I can't send this message or you can't receive it.
In other words, an error-corrected digital transmission is all-or-none. Either the data gets to its destination and is identical to the source, or it doesn't get there at all. It can't change along the way, no matter how much interference there might be, unless there's no or very limited error-correction.
Non- error-correcting protocols
are sometimes used, even for audio, but then the effects of interference -- data corruption -- are not subtle. Audio-wise, they're obvious and ugly and usually maximum-volume digital distortion, and they don't delicately overlay the good signal, they replace it entirely. When it happens, there's either music when the system works or hideous noise when it doesn't. The two aren't mixed, because digital mixing requires (relatively) complex processing by a computer; it can't happen via interference, even in a non- error-corrected system.
But that's an aside. Back to the media being paused...
When the media is paused, no signal data is transmitted, because the data transmission protocol stops sending
any data. No matter how much interference is present, even if electrical interference
could somehow be encoded as data in transit despite error correction, there isn't any transit happening to carry the electrical interference data.
In a closely-coupled home environment, the AC power grid and analog signal interconnections often provide an analog interference path to analog devices. It's quite easy for interference to travel from one part of the home into another part of the home's analog devices, despite using balanced connections. Balanced connections are not perfect interference removers. They're great for reducing normal environmental EMI noise over long analog signal cable runs, but they're not impervious and they won't help at all if the interference is introduced into the source analog device. In that case, the balanced connections simply carry the already-interfered-with signal.
It's difficult to say specifically what was going on in your system without getting you to partially unplug your UPS (you do mean UPS -- uninterruptible power supply, like those made by APC -- yes?) again, and then going through some diagnostics, consisting mainly of unplugging things and listening and noting results. If you're willing to do that, it would be interesting to find the specific cause.
Otherwise I think the noise was due to analog interference, carried by the inevitably close-coupled wiring of a home environment and affecting analog devices.
