[1] Well at least we agree the zeros and ones are not being changed.
[2] Well an IPhone compared to the DACs we all use on the forum are a little different. Firstly we all use mains power ( well most IPhones I see are plugged in charging most of the time but that's a different issue ) and [2a] secondly the iPhone DAC may not produce a sound capable to show a difference with or without noise ( but I see you point ).
[3] When I connect my Torus Power supply the difference in the USB cables are closer which would seem to suggest noise and USB cable interaction ( as the cable is the other variable ).
[4] If the DAC does not filter out noise do you suggest the DAC is faulty or the source of the noise...? Which may suggest why you think DACs may be faulty ...
[4a] I have no doubt as to noise entering though the mains and or into the USB cable ( poor shielding ) then into the DAC and being amplified on the analogue section and messing up the sound in someway.
[4b] Edit It could also be noise coming from the source ie server, laptop etc
1. Yes indeed. However, specific ones and zeros being changed in a specific manner is the only explanation which could account for many of differences typically described between USB cables. Unless of course those differences are not actually in the sound output but only in the listeners' perception.
2. It's not a different issue, it's all part of the same issue. Why would using mains power be different from using battery power? Yes, I've heard some audiophile explanations for why but those explanations are nonsense. Somehow, many audiophiles seem to have been convinced that handling mains power adequately is near impossible. This is simply untrue! It's untrue not just because science says so, it's untrue because competent electrical engineers say so and because there are a whole range of audio products, which have been on the market for many years, that actually demonstrate/prove this fact!
2a. Nope, iPhones have a very clean and linear output. The only potential drawback of iPhones is that they're not designed to power many of the bigger full size headphones.
3. Yes, I entirely agree! However, that observation misses the real point/question, which is: Why should a mains power supply and any USB cable interaction have any effect whatsoever on the output of a device advertised as a mains powered USB DAC? ...
4. I wouldn't put it quite that way but essentially yes, that's my position. I wouldn't put it that way because it's not really a question of a DAC actively filtering out noise, it's simply a question of competent design. The design of power supply handling, USB signal handling, grounding and isolation if done competently eliminates the possibility of noise anywhere near audibility getting through to a DAC's output. This brings us back to point #2 and how difficult it is to achieve this "competent design" or rather, how is it that many audiophiles seem to have been convinced that it's very difficult or virtually impossible? And, that DACs which do not achieve this level of competency are acceptable and furthermore, that it's then somehow acceptable to spend hundreds/thousands of dollars on USB purifiers, audiophile grade cables, audiophile grade power cables and power conditioners to cure the problems that any competent DAC design should have already eliminated.
4a. Case in point! If mains power is causing audible noise in your DAC's output, your DAC is either broken or has been incompetently designed. Likewise, if you need more shielding than is provided by a standard USB cable, it's because the isolation in your DAC is faulty or has been incompetently designed! So how difficult is this "competent design" really? Sure, at one time it was near impossible, then later it became possible but at a high price but today it's trivial, cheap and completely standard and expected ... except apparently in a segment of the audiophile world! If I bought a pro-audio DAC, advertised as mains powered, I would expect it to work optimally with mains power. If it didn't, if it required conditioned power to perform optimally (if conditioned power improved the output massively enough to be an audible improvement) I'd be straight on the phone asking for a replacement non-faulty unit or my money back if all their units are similarly faulty and, if it were the latter, I'd then be on the pro-audio forums warning others that it's a pile of junk to be avoided! Likewise with USB, if it required an audiophile USB cable and/or "purifier" to isolate from any audible USB power, computer or EM/RF noise, rather than the no brand USB cable it was probably supplied with. Just to be clear, I'm not talking about multi-thousand dollar pro-audio DACs, I'm talking about cheap $100 or so units, which have far higher component costs than audiophile DACs because they are also ADCs, include mic pre-amplifiers and have balanced and unbalanced outputs! So why can some/many audiophile DAC manufacturers apparently not achieve the level of competency achieved by pro-audio manufacturers for years, at a fraction of the price and which the pro audio community takes for granted? And why do many in the audiophile community apparently have such vastly different expectations of "competent design"? Ultimately the answer comes down to marketing, the desire/need of audiophile manufacturers to avoid the standard, proven solutions and attempt exotic designs which provide marketing opportunities/implications but fail to solve the already solved issues of isolation, power handling, etc.
4b. Another case in point. Any competently designed DAC should be isolated from server/laptop/source noise. Isn't the whole point of an external DAC to isolate from computer noise? All computers, servers and laptops produce significant noise, isn't your DAC designed to be connected to a standard computer, laptop or server? Can it only perform optimally with silent computers, servers or laptops, which don't actually exist in the real world? How is such a DAC not faulty or incompetently designed?
G
