Investigation Into Effects Of PC load On DAC Analogue Output

[idiot_savant]

Well, this is going downhill fast...

 

There is an interesting question here : To what degree is "sensitivity" a good thing? 

On the one hand, you want a low noise floor and low distortion, good filtering etc in a DAC and an ADC to reveal as much as possible.

You also want this system to be as immune as possible from external influences ( mains, EMC, etc ).

 

And yet - I often see it stated that a product is "sensitive" because it reveals some difference in cables, processing or suchlike that can be simply explained by being marginal engineering. For example, I could transmit a high speed clock between two devices ( think a transport to a DAC via I2S ), but I accidentally fail to terminate it properly. The cable is now very important to the performance because of the mismatched ends, to the extent you can probably make it crackle by bending the cable. The DAC is now very "sensitive" to the cable, so you can "improve" it by cable tweaks. However, the *best* it can ever be is the *same" as the same design properly implemented ( i.e. properly terminated ).

 

Which would we prefer?

 

@March Audio has been fairly clear that he is demonstrating a system that is based on off the shelf components, with no tweakery, using components he regards as well engineered, and can see no differences. This *isn't* to say he won't ever find any differences as he refines his measurements, but so far there is nothing to see.

 

Comparing this system to one where the reviewer explictly says it is poorly engineered and not galvanically isolated and exposing a problem merely shows the problems you can get with marginal engineering. 

 

As boring as it may sound, good engineering will remove a lot of the "randomness" that people seem to enjoy tweaking around. I don't know about anybody else, but I'd rather listen to a system that sounds the same irrespective of the phase of the moon,

 

your friendly neighbourhood idiot

[idiot_savant]

@SoundAndMotion there seems to be a bit of crossed purposes here. I myself have said on a forum, you’re unlikely to “convert” people who are entrenched, but if you let some of the more outrageous claims go unchallenged, people who are maybe unconvinced need a bit of a sensible voice to help a bit of balance?

I think the point @March Audio is trying to make *isn’t* that all PC’s with all DACs are perfect, but that with a bit of care, you don’t need a PC encased in unobtanium to get really good performance. 
 

As for specs, most well-engineered stuff tends to have a margin of error built in, and good engineering in one place *can* indicate overall good engineering, whereas bad engineering in one area tends to indicate a trend

 

your friendly neighbourhood idiot 

[idiot_savant]

@PeterSt - I’ve never asked you to quit this “hobby” - but I thought you were a manufacturer? Isn’t that different from being a hobbyist?

 

apologies if the language is coming between us

 

your friendly neighbourhood idiot 

[idiot_savant]

Now, strictly speaking, the complaints about PC activity have always been about “noise”, which IMD is clearly not ( clues in the name ). However, in a spirit of open-mindedness, I certainly wouldn’t object to such a test - maybe we should get the precise IMD setup required?

 

I can understand why @March Audio wouldn’t have done this - he’s been concentrating on noise, as this has been mooted as the problem. 
 

your friendly neighbourhood idiot 
 

 

[idiot_savant]

@PeterSt - maybe it would be helpful if you could describe the interface used within your tests? i.e. how is the DAC connected and powered? I believe ( happy to be corrected on this ) that @March Audio is using a DAC that is connected via USB with an asynchronous style interface, and is powered separately from the PC.

 

If your tests were using, for example a synchronous interface, or USB in adaptive mode, or the DAC is somehow powered by the PC, this might give us some insight?

 

 

your friendly neighbourhood idiot

 

[idiot_savant]

@Summit - nobody is suggesting that deliberately ignoring PC noise is desirable, but you have to consider a fundamental point here - we’re not trying to stop noise getting out of the DAC using filters. Surely in an ideal DAC, the electrons that represent the digital samples have *can’t* get to the analogue out? The whole point of digital electronics is its an abstraction - I.e. as long as the samples get to what needs them in time, it’s completely irrelevant how they get there - paper tape, punched cards, Ethernet, USB, a really fast typist. 
 

your friendly neighbourhood idiot 

[idiot_savant]

Polluted with what?

 

 

 

your friendly neighbourhood idiot 

[idiot_savant]

Right, so where is this pollution on the measurements provided? @March Audio hasn’t taken any outrageous measures, so maybe we’re worrying about nothing?

 

When you say signal is polluted with jitter etc do you mean the samples are corrupted somehow? Delivered at the wrong time?

 

I’m genuinely interested - “signal” could be the actual audio samples, or the USB packets, or the output from the DAC itself

 

 

your friendly neighbourhood idiot 

[idiot_savant]

Erm,

 

If you’re not interested, why post?

 

This sub-forum is the objective forum. If I can’t work out what “signal” means from your statement, and I am an idiot, if you can’t help me out, what can I do?

 

 

your friendly neighbourhood idiot 

[idiot_savant]

Ok, 

 

thought experiment time - we’ve got the designer of the best DAC in the world, but he’s obsessed about EMC/RFI/jitter, so the only interface he provides is punched cards. 
so, he sets up his system, so it  starts  reading in red book audio into a buffer when he presses start, and there’s a button, let’s call it “end of file” that says we can start playback. 
so, he loads up “wish you were here”, waits about 7 hours and puts in his ear defenders until the last card is read. 
he presses “end of file”. 
the DAC starts playing. Was the fact there was someone playing a trumpet in the room in the previous 7 hours make a difference?

 

*edit* euro 2020 has started, so this analogy not quite as thought through as I’d have liked

 

your friendly neighbourhood idiot 

[idiot_savant]

Wish you were here, punched card official photo - see how happy we are to be free of jitter and RFI

[idiot_savant]

Right, so the point of this thread ( I believe )  is there are certain people who reckon you have to go through many, many hoops to get good playback from a PC. Typically those same people claim that even though you *need* to go through these hoops you’ll get better sound than from anything else. When pressed as to what these hoops solve, hands start getting waved, and typically some nebulous “noise” is being generated somewhere that you need to reduce. Being Objective type people, all this hand waving and nebulous claims makes us unhappy. 
So, we assume that the “noise”  is electrical rather than acoustic, and look for it influencing the output of a DAC on a non-tweaked system. And can’t find it.

 

And to those people who claim FFTs are poor for detecting noise, or “average it out” I’d advise them to do some research. FFTs are poor for glitch detection, but incredibly sensitive for just about everything else, but do need a bit of interpreting

 
PCs are noisy due to switching noise - every time something is turned on, or off, it generates a tiny amount of noise - the problem is a PC typically has millions if not billions of things all turning on and off at mind boggling speeds, some at the same time, some not. ( so your CPU and GPU will generally have independent clocks ). 
 

Nobody is trying to tell you which DAC is good, or even which DAC sounds the best, you have to draw your own conclusions 

 

 

your friendly neighbourhood idiot 

[idiot_savant]

@PeterSt - you say you’ve spent many years trying to optimise DACs and PCs/ software, which I believe. So, I’ve never seen you share these improvements/optimisations, apart from that you sell some kind of bespoke system? 
How annoying would you find it if a competitor came on here and just kept say “haha - I know this” repeatedly? 
I understand if you believe you’ve discovered some secret sauce, but just saying you have a secret sauce doesn’t make it fingerlicking good?

 

your friendly neighbourhood idiot 

[idiot_savant]

@botrytis- you fool, you’ve forgotten the golden rule - audio has ethereal properties that can only be captured with random noise and distortion. I’m pretty sure if you chanted “ommm” while capturing, your results would be, er, better, or faster, or more “close to the original”. 
 

Your friendly neighbourhood idiot 

[idiot_savant]

Probably make you cry as well

 

 

 

 

 

your friendly neighbourhood idiot 

[idiot_savant]

I do apologise if I appear flippant, but I think the point remains - audio is incredibly important to many people, for very good reasons - but how is it harder than other things? A picoscope, for sake of argument captures data at precise moments in time. And transfers it’s results via USB but I don’t recall anybody having to do fancy things to have it work properly?

 

 

your friendly neighbourhood idiot 

[idiot_savant]

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 

 

[idiot_savant]

So I suppose something I would say is that (again) we have a fair amount of hand-waving from some quarters. If you are unhappy with FFT analysis, and have a better way of objectively proving something, please feel free to put it forward. I'm not going to say @March Audio will peform any test you throw at him but just saying "I don't like the way you're testing" isn't going to get us anywhere.

 

 

He's put some thought and effort into this, which should be appreciated - somewhat more than waving his hands in the air and making "what-if" statements

 

 

your friendly neighbourhood idiot