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Investigation Into Effects Of PC load On DAC Analogue Output


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On 6/10/2021 at 10:14 AM, firedog said:

Maybe you didn't read the whole thing at ASR or the other threads on the topic. The point was the ISO Regen lessened the noise, but only with a DAC that is essentially "broken" b/c of improper design. With other DACs it made no difference. 

Same for other DACs - except for a small minority that are improperly designed, March Audio's results hold. Conclusion: the PC doesn't matter for these measurements, unless you have a DAC that is inherently defective. 

Archimago did similar testing at his site a while back and got the same results. 

 

My own listening tests over months have likewise indicated to me that the ISO Regen helps certain DACs and doesn't help other DACs. The DAC that it helped was otherwise quite good and quite cheap so no problem with isolation devices when needed.

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17 hours ago, March Audio said:

Please ask questions, it's a complex subject.  I'm sure between myself, @pkane2001 and @idiot_savant we can make it more understandable.

 

Indeed, controlled subjective listening tests are something I intend to move on to.  Will take a bit of time and organising however.

To be clearer, I don’t have any issue with your measurements. You’ve clearly stated that they apply to your specific tested equipment.
 

The arguments that I find incomprehensible are those which argue that you are wrong or haven’t tested appropriately. This argument is old enough that anyone who wants the “prove” that x, y or z causes and audible difference, need themselves to present a clearly understandable graph/measurements. The measurement techniques are all very well described. The physics of electronics is all very well known. That said there aren’t comprehensive measurements so who knows what is real. It’s trivial to show that two cables measure differently but there are few demonstrations that this causes a difference at the DAC output. Obviously speaker cables cause electrical differences at the speaker inputs. 

 

That said taking a condescending tone doesn’t do anything to help whatever cause you may have. The archives here contain any objections I have to measurement assumptions, namely I don’t want to bandwidth limit the output signal in any fashion to allow all non linearities to present themselves but I’m not going to repeat those arguments here in detail, the point stands that if anyone objects to your findings they are free to repeat your measurements and use different equipment and/or better techniques as they see fit. This isn’t a dead horse that I care to make into glue.

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3 hours ago, botrytis said:

Well, if I can use USB to collect all data from a MS, that will collect AMU (Atomic Mass Units) from 10 to 1000 AMU 60 times a second for 2 hours w/o any issues and also control the MS and the GC feeding it, I think USB can handle music. 

I know you guys are joking but this is the same issue as using logic to decide what you should hear.

 

The simple objective fact is that the USB signal presenting at the receiver need not be close to a true square wave, and the digital systems tolerate quite a bit of input ringing. Its certainly conceivable that certain DACs do not adequately filter out the ringing and so small changes such as rise time etc might have an effect that makes it to the DAC output -- the DAC really needs to be treated as an analog device at some point. **might** make a change. It would need to be measured. All the rest is speculation and assumptions until the DAC output is measured by someone who cares ... and not just 20-20kHz ... full band, I mean a 1 MHz or GHz oscillation might make a difference ... I had that happen once with an unstable I-V converter that was missing a gate stopper... sounded like ass. The only problem was that the factory which made the part changed ... little stuff can make a difference unless thorough measurements.

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1 hour ago, March Audio said:

No they aren't joking.

 

Why do people think that audio is some how special?  That it evades the laws of physics and scientific investigation?

 

I never suggested audio is different nor that it could evade the laws of physics and scientific investigation.

 

There is no law in physics that says that a USB cable can never alter the SQ of a particular DAC, nor is there a law of physics that prohibits server load from influencing the DAC.

 

Electrical physics is very well known and accepted. Do Maxwell's Equations say anything about cable or server load audibility? Unless they've changed since I was in school: zilch.

 

1 hour ago, March Audio said:

 

Actually this isn't based on logic about what you can hear.  It's based on probably 100 years of scientific research of Psychoacoustics.  I mentioned above some of the research into the audibility of jitter for example.

 

What we see from some people is just Han waving, "oh we might be missing something", when they haven't even conducted controlled listening tests to remove their own biases.

 

On the other hand you are completely misstating what the "Laws of Physics" actually say on the topic: zero.

 

Seriously the so called "scientific research" on psychoacoustics isn't really there either. Believe me.

 

That said there are a lot of implausible and fanciful arguments that have zero scientific support. As far as I am concerned I am sufficiently certain that my fiberoptic Ethernet electrically isolates my server from my DAC that I am not concerned with this topic. As far as I am concerned people should use good solid electrical design and the illusion that bits are just bits works for our everyday purposes.

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Just now, March Audio said:

I didnt suggest you did :)

 

Oh for sure, but we have suggestions from some that the manifestation of these alleged effects are beyond measurement.  Its somehow magic that cant been seen.

 

Everything is measurable with sufficient motivation even gravitons and mesons.

 

Just now, March Audio said:

 

Sorry I dont mean to be rude but thats rubbish regarding psychoacoutic research.  How do you think compressed formats were developed?  Audibility of kitter has been researched, etc, etc etc.

 

Let's just say that my faith in the conclusiveness of this research does not rise to my faith in Maxwell's Equations ;) Compressed formats do not take into the nonlinearity of the human brain i.e. cable color does actually affect SQ because the visual system affects the auditory system at the cortical level. I'll stick to electrical output of the DAC thank you.

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2 minutes ago, March Audio said:

well measure single ended ;)  Thats actually one of the tests I will be dong as the Gustard has XLR and single ended outputs.

 

Again its just more nebulous hand waving.  Lets be clear about this, these are effects that some audiophiles claim they hear.  Yet there is no controlled subjective testing that confirms these things are audible.  "Chasing Ghosts" springs to mind.

Single ended ... errmmm common mode is common to the signal and ground ... seriously (it is very tricky to deal with)

 

If you think that common mode noise is just nebulous hand waving you need to go back to school -- of course this is an example, a plausible example nonetheless. But man its just freshman electronics...

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1 minute ago, March Audio said:

you will lose the common mode rejection hence it becomes more visible.

idk balanced does differential mode noise rejection. fiber rejects common mode noise. again its tricky.

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7 minutes ago, March Audio said:

Seriously, you think that balance connection dont perform common mode rejection?

 

For the purposes of our discussion here USB is balanced. Copper ethernet is balanced. Neither entirely block common mode noise. The topic is too complicated to debate this way. Ground loops are one type of common mode noise that balanced connections block. I'm referring to the broader wide band common mode noise that isn't blocked simply by balanced connections i.e. the kind that would be relevent to this discussion.

 

Peace.

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On 6/14/2021 at 6:53 PM, idiot_savant said:

Erm,

 

sorry to be pedantic, but this thread is about PC load? Can that change common mode noise? If so, surely we can measure it? As for ringing, it’s not showing up on the DAC output? The thread is about common conceptions  - if the DAC used in the test is “too good”, can someone suggest one more likely to show differences?

 

 

 

 

 

your friendly neighbourhood idiot 

 

PC load most certainly can and has been shown to affect common mode noise. There is a measurement of this in one of my classic textbooks on high speed digital design/RF mitigation etc. I can't recall which off hand. I'm going to guess Ott but if not then Johnson.

 

In my experience the Pre Box Digital S2 which is an outstanding though very cost effective DAC is more input sensitive than the iFi iMicro DSD to keep this discussion to commonly available and relatively inexpensive DACs that I like the sound of.

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  • 2 months later...

The premise that bit perfect playback sounds identical is fundamentally flawed. 
 

Imagine these software settings: 

A: do not inject common mode noise into USB power/ground 

B: inject maximal common mode noise into USB power/ground

 

It should be obvious to anyone that ground loops exist and are audible. 
 

If this were known to be the setting no one would question the results. The problem are undocumented settings whose action have not been explained. The really scientific was to explain a black box is to open it up and look inside. ie reverse engineer — if anyone cared. 
 

Short of that this argument is pointless.

 

I am not saying that common mode noise is the mechanism just that it would be a possible mechanism — there are others : you could send signals down the USB power-ground, you could vary the USB d+|- within allowed values etc etc etc 

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7 hours ago, PeterSt said:

 

What !?

 

If we change the story somewhat, then I ever back created playback software which today sounds better to anyone trying it out of the box, which means : in Demo mode, while 95% of (bit perfect) SQ features unleash when activated.

And now you are going to ask me how I do that, right ?

Don't expect any perceived clear answers, because from A to Z you won't believe a thing of anything. And if you are going to measure the (by others) perceived differences, then you won't believe one thing of it all definitely. 😉

Still I myself showed the differences easily, and you know it ...

... But there we go again ... those minute differences can't be audible.

 

 

How about this, forget what you think people will or won't believe state:

1) clear answers

2) describe how the software changes the timing

3) or how the software is changing the electrical signal

 

You are treating this too much like a trade secret and I'm afraid your software is not getting the attention it might otherwise deserve. Contrast this with HQPlayer which does a fair amount more documenting filters and modulators and has seen a  much higher usage growth.

 

Tell us what the settings do. 

 

You are being too coy. Shed some light.

7 hours ago, PeterSt said:

 

 

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33 minutes ago, manisandher said:

 

IIRC, the auto-start did something weird like swapping the channels (for the first ~45ms)... of just a few of the digital captures. None of the analogue captures displayed this behaviour, and so the 'glitch' in the digital capturing equipment had no bearing whatsoever on what I heard during the test. I can look into it further when I have some time, if you'd like.

 

But quite honestly, I'd be more inclined to use my time in repeating some tests using my RME.

 

Yes for those of us who understand that as an analogue device, it is the analogue input to the DAC which determines sound as opposed to the interpretation  as bits.

 

As such I am interested in changes in the analogue output of the DAC. It would be great to demonstrate that clearly.

 

My very firm opinion is that if there is a real audible difference in sound (not just SQ) then there will be a real difference in analogue DAC output. A failure to demonstrate that will necessarily be a failure to measure correctly. I am not placing any requirements on what the analogue changs are, nor whether they are bandwidth limited.

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