Investigation Into Effects Of PC load On DAC Analogue Output

[March Audio]

4 hours ago, manueljenkin said:

Just because it's not measurable with present state of apparatus doesn't mean it doesn't exist. Has happened in science many times, that a top level abstraction is shattered with a new discovery bringing life to older approaches that were earlier ridiculed.

 

I don't think anyone here has demonstrated lack of knowledge. You seem to be adamant that there is a magical fix down the line that can remove "all" aberrations introduced by noise from pc ground planes while the only measurements you have are mostly uncorrelated to real world audio signal performance, and some of the issues beyond that has already been demonstrated by John Swenson and others. 

 

Measurements are great, but conclusion is not. Objectivity is different from science. If required to be objective one can rank cows by their aerodynamic structure, but would it make any sense?

Sorry but this is the standard reply trotted out by those that have no ability to justify their beliefs.  It's pretty unimaginative TBH.

 

This is an objective thread.  Your faith has no place here.

 

I have just stumbled across this which makes the point.

 

https://archimago.blogspot.com/2021/01/musings-noise-jitter-faith-autistic.html?m=1

 

[March Audio]

4 hours ago, manueljenkin said:

Was this article peer reviewed? Remember, this is an objective forum.

If you want to question the technical credibility of Bruno Putzeys you go ahead.  Best of luck.

 

Also the fact that his class d designs use massive amounts of negative feedback and don't suffer the alleged "1970s amp bad sound" sort of proves the point that negative feedback is not a problem, quite the opposite.

[March Audio]

Oh just as an aside, if anyone thinks the audibility  jitter is anything that hasn't been very well researched for many years, then take a look at this BBC research paper from 1974.

 

https://www.bbc.co.uk/rd/publications/rdreport_1974_11

 

http://downloads.bbc.co.uk/rd/pubs/reports/1974-11.pdf

[March Audio]

2 hours ago, manueljenkin said:

So you don't have a peer reviewed paper for the same! Just your anectodal experience.

 

There's nothing about faith here. I just mentioned that your tests objectively don't provide full coverage to fully conclude on any of the modulations and the audibility (if so, it would require you to first conclude everything about human hearing and weights to different fidelity indexes before you could trickle down to the rest). And a bit of history on why science and objectivity aren't completely the same, just to let you know you can't make "conclusions" at will.

OK, please explain the faults in the paper.   Know you can't.  You are trying to spread FUD.

 

I never stated those tests did.  You have misunderstood.  I haven't made any conclusions.  This is just an investigation, one that's not complete.

 

 

[March Audio]

2 hours ago, manueljenkin said:

Oh yeah, trying to derive conclusions from a paper about jitter effects from 1974 when the whole domain of phase noise analysis methods was described to fair accuracy only after 2000s.

You appear to have a lack of understanding.  I was merely pointing out, as clearly stated, that the audibility of jitter has been thoroughly studied over many decades.

 

The levels of jitter that are required to becaudible are actually quite high compared to the levels seen in dacs these days.

 

Yet there are assertions in this thread that imply the tiniest, immeasurable of levels are audible.  That is not consistent with the decades of research into the phenomenon.

[March Audio]

2 hours ago, manueljenkin said:

 the whole domain of phase noise analysis methods was described to fair accuracy only after 2000s.

You didn't read the paper did you?  You didn't notice the parts about sinusoidal and random jitter stimuli.

[March Audio]

2 hours ago, manueljenkin said:

 the whole domain of phase noise analysis methods was described to fair accuracy only after 2000s.

This is not correct.  Phase noise was known about and measured long before then.  I suggest you do some research.

 

One example from 1987, but hardly the first.

 

https://www.hpmemoryproject.org/news/3048/hp3048_01.htm

 

 

 

 

 

[March Audio]

The HP 3048A System appeared for the first time in the HP general catalog in 1987, it was the successor of the 3047A which was born in 1983.

[March Audio]

1 minute ago, semente said:

 

I had read that paper before. It says that:

 

"If there is a relationship, it has to be through the behaviour of the specific circuit implementation. For a given GBW, slew rate is a fixed quantity and slew induced distortion can be predicted exactly from the ratio of actual to maximum slew rate. Nothing will reduce SID other than improving slew rate unless we modify the circuit."

 

I don't see any discrepancy between perceived audible distortion and engineers not wishing to believe it.

The blame was put at the door of negative feedback which is not correct.

[March Audio]

1 minute ago, semente said:

 

So the Putzeys is correcting Otala. But does he deny TIM audibility and engineers not wishing to believe there was something wrong?

Was it a case of engineers not wanting to believe it?  

 

Storyline 3: Marketing hype, specmanship and “lots of zeros”.
During my tender years, “Japanese Transistor Amps” were held up as prime examples of things that measured well and sounded terrible.  remember the 80’s when we were flooded with amps that had 0.00001% distortion.....

 

.......That doesn’t mitigate that the leaflets were misleading. Sometimes subtly by stating only THD at 1kHz/1W, often more brutally through a technique called lying. These amps didn’t measure at all well and they sounded the part.

 

Bruno is saying it was marketing.  That's quite different to saying there was a refusal to believe there was an issue.

 

Anyway, how does this apply to the situation today?  Do we have components that sound awful despite good measurements?

 

I keep asking people to provide such examples and they never do.

 

In this specific case we are looking at here, the people who are claiming audible differencesccant provide on jot of supporting evidence beyond "I hear it therefore it is".

 

[March Audio]

5 hours ago, jabbr said:

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.

I don't havexany cause.  This is an investigation.  Will it test every combination of dac / pc on the planet?  No.  It will however start to lay some facts down about what really happens instead of the unsupported claims, hand waving and inaccuracies seen from some people.

[March Audio]

1 hour ago, jabbr said:

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.

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?

 

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.

[March Audio]

1 hour ago, jabbr said:

. 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 ... .

For there to be audible differences the end effect needs to be in band, ie below 20kHz.

 

To be clear about what I'm saying, that doesn't preclude out of band issues causing in band ones, but the point is the problem will be seen if it manifests in band.

[March Audio]

1 hour ago, jabbr said:

 

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 

OK, so how might that manifest?

[March Audio]

Considering that the data from the usb receiver is subsequently buffered and clocked out by a separate low phase noise clock.

[March Audio]

1 minute ago, jabbr said:

 

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.

 

 

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.

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.

 

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.

[March Audio]

3 minutes ago, jabbr said:

How might it? Common mode noise *might* sail right through the digital section of the DAC and affect the analog output. It really might. Im not saying that it does or does for every design but it might.

 

To be clear assuming that something **can't** happen just because you can't imagine how it would is not science. To disprove my above hypothesis for a particular DAC, you would need to apply common mode noise of varying intensities to the inputs and measure the outputs.

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.

[March Audio]

1 minute ago, jabbr said:

 

Everything is measurable with sufficient motivation even gravitons and mesons.

 

 

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.

Sorry you have lost me.  You may have a misunderstanding of what the science of psychoacoustics entails.

 

Well MP3 and AAC work.  Built on the study of how we hear things.

 

We are looking at the electrical output of the DAC.  

 

 

[March Audio]

1 minute ago, jabbr said:

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

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

[March Audio]

3 minutes ago, jabbr said:

 

 

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...

Eh? I never said that.

[March Audio]

5 minutes ago, jabbr said:

idk balanced does differential mode noise rejection.

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

 

Sorry but you haver just given the game away.  You might want to re-visit your "freshman" lectures.

[March Audio]

3 minutes ago, jabbr said:

 

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.

That is irrelevant.  We are only interested in what comes out of the DAC.

 

Please go back and read the thread.  I have mentioned the effects ground loops, and noise currents multiple times, even in the OP.

[March Audio]

In post 4? I even showed the effects that can happen.

[March Audio]

1 hour ago, idiot_savant said:

Erm,

 

 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 

 

And doesn't this just reinforce the comments earlier in the thread, ie that it's obviously quite possible to engineer a dac that isn't sensitive to these problems.  It isn't a virtue for a dac to be sensitive to these problems.

 

It appears to me that people look at the problem backwards.  Pcs are noisy. Period.  They are also very variable in this respect. If you really are hearing problems then dump the offending dac. 😉

 

Anyway, to be clear I haven't finished looking at dacs, I can test as many as I can get my hands on.  This is an investigation, not a statement of "I have proved X".

[March Audio]

1 minute ago, One and a half said:

@March Audio, In revisiting this thread and the graphs on page 1, the PC is shown at idle. 

Most DACs I know of remain muted and if there's no incoming signal to process and display the last current state and don't perform any work.

 

The graphs would be more meaningful if the PC was actually playing a file (doesn't really matter what type) and the DAC is processing and performing what it does. The idle PC shows, predictably no difference in the DAC output cause there's no work to do.

 

Or am I missing something?

 

Sorry but you misinterpreted the plots.  The dac is playing a -60dB 1kHz tone, so it's working away 😀