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This can't be right - my CD's digital end seems to affect sound quality more than expected

post #1 of 64
Thread Starter 

Gah - Houston, we have a problem...

 

My wife and I just finished a couple of hours worth of blind testing (using my Mirage M3 speakers) where it wasn't known to the person tested when [1] the CD (a Tag McLaren) was played through my NuforceHDP (which is my headphone amp that also has a DAC/pre-amp to those who don't know it) via coaxial (digital), [2] via analogue, [3] via the computer CD to the HDP using coaxial, or [4] via high quality .ogg (Spotify) to the HDP using coaxial. I of course expected that the .ogg would be notably worse from not being lossless. This part was confirmed by both of our results, and thus isn't the problem we had. Granted - the difference isn't earth-shattering, but it clearly removed the low end impact and also some of the body in the mid range on the better recorded albums.

 

What's more remarkable is that we both identified the CD through either [1] coaxial or [2] analogue as one clear step ahead of the other options. I put the analogue slightly before the coaxial, but my wife couldn't separate them which shows how close those two are. At this point, my hypothesis that the analogue part of the DAC in my CD player would be better than the HDP holds (although marginally only, but I am extremely used to listening to it through analogue cables to the tube pre-amp I normally use instead of the HDP pre-amp that we tested tonight). Something was fishy here, though, as I fully expected the coaxial option [1] to be behind the analogue option [2] given my hypothesis about the analogue part being quite good in the Tag McLaren. This was proven a correct suspicion as my second hypothesis that the computer CD to the HDP via coaxial [3] should be very close to the sound of the Tag McLaren CD using coaxial [1] did not fare well. I was so certain before this blind test that the only reason I favored my Tag McLaren still was due to the analogue part. However, we both noted the computer CD to HDP over coaxial [3] to be one notch down vs. the Tag to HDP over coaxial [1]. This is what concerns me, as the results indicate that something on the digital end of the Tag makes a difference that we both noted as 'big enough' to be considered noteworthy. The relative difference in low end impact between analogue or digital from the Tag to the HDP (i.e. using the CD's DAC or the HDP's DAC) is much smaller than between the coaxial Tag and the coaxial computer CD (always using the HDP's DAC, but with two different digital sources).

 

These conclusions were reached in blind tests and we're both scientists and extremely familiar with how to act in order to not cue test subjects in on results. Of course, to be considered scientifically valid, tons more is needed that we're not interested in pursuing just to 'prove' the results. However, the situation baffles me as I expected something else than the results showed. Since we were both quite confident in our analysis (again - being scientists, we know very well when we feel confident enough to take a stand and when to say we're not certain of something), I've started to ponder what it could be that may potentially affect the digital end and lead to a decreased low end presence which to some (but less) extent spills over into the mid range (this is harder to know for sure if we actually perceived, or if the better bottom end tricks our brains into believing the low mids as also affected). I'm looking for speculative and suggestive advice here, not an argument regarding 'truth' that belongs in the sound science section. 

 

I would have called this a bogus result if I hadn't been part of the test myself, so consider me the first skeptic in line to instead want to believe in the initial two hypotheses. Seriously - what could affect the digital end in this way? Would the differences in power supply from the two sources (where my stand-alone CD obviously has power supply that operates in a much better environment than the computer CD power supply does) actually affect the results (in this way)? Anything else??? I'm drawing blanks and doubting our own results at the same time, and we did perform these tests repeatedly and had no differences in the results once we honed in on which albums best illustrated the differences.

 

We never tried the test using headphones instead of speakers as the bottom end is so much more clearly heard on my speakers (not to mention that I care much more about my speaker setup than my headphone one to be brutally honest [lynch mob, beware of falling mono-blocks!]). 

 

Edit: Why do I always spell check and grammar check afterwards?


Edited by Trasselkalle - 8/27/11 at 12:56pm
post #2 of 64

I'm not sure I completely follow but there is no guarantee of level or even frequency response matching between analog and digital paths in a amp/DAC

 

the two paths must be matched to 0.1 dB level ( 1% AC Voltage match) or you will be expected to hear that - below a few dB most will not recognize a level difference as a loudness difference so matching level "by ear" is not good enough - you need to measure

 

a soundcard with line inputs and a couple of R dividers is one way of level matching - would allow RMAA test of frequency response too

post #3 of 64

Both of you being scientists, you should also know two more things:

 

1: Correlation doesn't equal causation.

 

2: Subjective reports are not very reliable indicators minute changes in complex systems.

 

As such, I would agree with JXC that measurement is needed if this analysis is to be used in determining causation. 

Also, it's not clear what sorts of criterion you're using to rate a positive change in sound vs. a negative one.

post #4 of 64
Thread Starter 
Quote:
Originally Posted by Dr. Strangelove View Post

Both of you being scientists, you should also know two more things:

 

1: Correlation doesn't equal causation.

 

2: Subjective reports are not very reliable indicators minute changes in complex systems.

 

As such, I would agree with JXC that measurement is needed if this analysis is to be used in determining causation. 

Also, it's not clear what sorts of criterion you're using to rate a positive change in sound vs. a negative one.

 

 

Both of us being scientists already know - as stated in the initial post - that the tests aren't scientific. That was never the intention. This is a subjective test where we have looked to minimize the risks from knowing which alternative is used when conducting it. Subjectively, we're noting differences that are too big to simply shrug off as 'fluke'. 

 

Please (EDIT: and I do mean this kindly, not as a snide reply) - we're not after discussing the test procedure - we're after what could potentially make the strictly digital end of the Tag McLaren one step up in terms of low-end impact.

 


Edited by Trasselkalle - 8/27/11 at 11:37pm
post #5 of 64
Thread Starter 
Quote:
Originally Posted by jcx View Post

I'm not sure I completely follow but there is no guarantee of level or even frequency response matching between analog and digital paths in a amp/DAC

 

the two paths must be matched to 0.1 dB level ( 1% AC Voltage match) or you will be expected to hear that - below a few dB most will not recognize a level difference as a loudness difference so matching level "by ear" is not good enough - you need to measure

 

a soundcard with line inputs and a couple of R dividers is one way of level matching - would allow RMAA test of frequency response too


Sorry - I should have made a short re-cap of the core problem.

 

Summarizing, our results indicate that this low-end impact is there regardless if we use analogue out or digital out (i.e. the Tag's DAC, or the HDP's DAC) as long as the Tag is used as player, but that a reduction in low-end impact is there if we use the computer's CD as digital out (i.e. using the HDP's DAC, and when comparing with how things sound with digital out from the Tag = using the HDP's DAC but a different transport). 

 
 
Responding to your questions:
 
In terms of the analogue vs. digital paths, I know and understand that they will be different in terms of levels and frequency response. That's why I was expecting that the Tag had a better analogue end of the DAC than the HDP does (granted - a difference only I could pick up, but still) as this would have explained why I still prefer my Tag over the HDP when playing CD's. 
 
In terms of volume level, the low end is improved even if the volume is lower for the TagCD-to-HDPdac compared with the volume level for the ComputerCD-to-HDPdac. We're talking deeper bass in terms of frequency (I'd estimate below 50 Hz but it's tricky to know where without measurements) and something that is heard regardless if the overall volume is lower (i.e. clearly heard as lower) when playing the Tag. We're thus not being tricked by the volume level, but yes - this would indeed be a first candidate for suspicion.
 
I'm afraid I don't have easy access to equipment for taking measurements. This is why it's an important aspect that neither one of us becomes tempted to speculate beyond what is clearly and repeatedly detected in blind tests. It gives better results to repeatedly say 'not sure' than always try to say 'possibly...' and have the 'possibly' end go all over the place. 

 

The core question I really have is: could there actually be a difference in terms of low end impact which primarily originates in the digital end of the source/transport? I certainly struggle to understand why this would be the case myself, and thus turned here to get some help in figuring potential reasons out.


Edited by Trasselkalle - 8/27/11 at 11:13pm
post #6 of 64
Quote:
Originally Posted by Trasselkalle View Post

The core question I really have is: could there actually be a difference in terms of low end impact which primarily originates in the digital end of the source/transport? I certainly struggle to understand why this would be the case myself, and thus turned here to get some help in figuring potential reasons out.

 

The answer is YES, of course the digital source can affect SQ, as experienced by countless subjective/anecdotal reviews.

 

And NO, I don't know why. It's customary at this point for someone to mention jitter, or noise (injected into the power and/or signal circuits), but this will just spark of a futile, circular argument, with lots of deliberate misinterpretations of the other side's viewpoint.

 

So just keep an open mind and enjoy the better sound that you end up getting.

I'd be interested in knowing the reasons as well, but sadly, I just don't think it will happen anytime soon.

 

 

post #7 of 64
Thread Starter 
Quote:
Originally Posted by TheAttorney View Post

The answer is YES, of course the digital source can affect SQ, as experienced by countless subjective/anecdotal reviews.

 

And NO, I don't know why. It's customary at this point for someone to mention jitter, or noise (injected into the power and/or signal circuits), but this will just spark of a futile, circular argument, with lots of deliberate misinterpretations of the other side's viewpoint.

 

So just keep an open mind and enjoy the better sound that you end up getting.

I'd be interested in knowing the reasons as well, but sadly, I just don't think it will happen anytime soon.


I was afraid this would be the case. I also agree that yet another circular argument chain would lead nowhere (in fact - that's why I posted this here rather than sound science). This is also why I was more after similar experiences and potential impact sources rather than 'true' answers. It may be naive of me to hope for that, however, but I'd be glad to be proven wrong by having people chime in on what may cause differences. As long as everyone stays clear of declaring that they know something is one way or another... maybe we wouldn't end up in a do-over of this discussion?

 

I'm not, after all, trying to definitively answer this once and for all - only trying to find what more I could potentially look into as affecting the deep end of a digital source. I'd be first in line to ask a moderator to lock down the thread if it ends up circular however.

 

post #8 of 64

So you are saying "digital sources (CD readers) make sonic difference".....

 

 This is known for a while (though a lot of people don't agree), it is why people spend $1000's on high-end transports.

post #9 of 64
Thread Starter 
Quote:
Originally Posted by AudioCats View Post

So you are saying "digital sources (CD readers) make sonic difference".....

 

 This is known for a while (though a lot of people don't agree), it is why people spend $1000's on high-end transports.


Well I can hear that there is a difference. I'm asking for the potential reasons.

 

However, I'm starting to seriously doubt the constructive contributions that I may receive in this thread, which is too bad as I thought that's what a forum like this would be about.

 

post #10 of 64

Strange thing you find it strange that the cd transport makes a difference. In my experience, the transport is hugely affecting sound quality, much more than the dac in many cases. I suggest you take a look at the Lampizator page on the transport issue.

post #11 of 64

Thank you for making this clear. I was completely confused reading the OP. Trasselkalle really trasslar till saker och ting.

 

Quote:
Originally Posted by AudioCats View Post

So you are saying "digital sources (CD readers) make sonic difference".....

 

 This is known for a while (though a lot of people don't agree), it is why people spend $1000's on high-end transports.



 

post #12 of 64
I'd strongly recommend level-matching before drawing any conclusions.

It isn't expensive, either. You can use a $5 DMM from Harbor Freight.

DACs and CD players have a small amplification section in them to boost the signal enough for a preamp to use. They all have different outputs and this is where the claimed "difference" usually lies. People are sensitive to sound levels.
post #13 of 64
Thread Starter 
Quote:
Originally Posted by Uncle Erik View Post

I'd strongly recommend level-matching before drawing any conclusions.

It isn't expensive, either. You can use a $5 DMM from Harbor Freight.

DACs and CD players have a small amplification section in them to boost the signal enough for a preamp to use. They all have different outputs and this is where the claimed "difference" usually lies. People are sensitive to sound levels.

 

The amplification is in the analogue part though, isn't it? At least I assumed it would be. Oh, and as noted earlier - even at lower sound level, the depth in terms of frequency is better from the CD regardless if it is digital out or analogue out. 

 

 

post #14 of 64

I had a discussion with my brother this weekend, when I mentioned the differences i had experienced between various digital sources, his reaction was the standard "how could a digital source make so much difference, after all it is just zeroes and ones right?".

No it is not, zeros and ones are imaginary concepts that do not exist in the material world, what goes over the line are pulses, with their form and timing. Deviations from the square, perfectly timed puls in all kinds of forms is called jitter.

What also goes over that line is pollution, there are usually many high frequency switch devices with their resulting fields in the sending device, EMF.

And parts of the chain can act as a RFI receiver, we all know how many radiostations you can get on 1 meter of simple wire. The power itself could be polluted in the sending device, travelling to the receiving device.

Pollution can deregulate feedback circuits that are used in almost all amp stages, also in source components and in opamps.

It depends upon the circuits of the receiving device how well it is able to reject this pollution. The less good it is, the larger the difference will be between clean and dirty signals.

Very basic first indication: dull undetailed sound usually is jitter, a sharp unpleasant sound are feedback circuits, of course you can have both at the same time.  

 

post #15 of 64
Having read the first post in this thread in its entirety, I feel it is my duty to ask please for the love of God don't be so verbose!

The computer may be using software that alters the music before outputting it to spdif. http://www.head-fi.org/t/221237/asio4all-explanation

If that's not the culprit, I believe that it may be jitter differences. I think bass depth/impact is one of the best things to listen for when trying to hear jitter, since drums have a predictable impact and decay across a wide frequency range. Some measurements have been taken by someone who writes low jitter media players suggesting that measuring at the dac analog output shows jitter differences better than at the transport's digital output. I would venture to suggest that at the speaker cone is where the jitter differences become most measurable. A sound with a sharp attack in many frequencies may be particularly affected by the most common types of jitter, because telling the cone to incorrectly move even at an inaudible frequency may have a more notable effect on other simultaneous cone sounds than oscilloscope measurements may suggest.

The comparison of hdp and cd player should take into account the fact that the transfer of digital data from cd player to hdp is likely inferior to the direct digital inside the cd player.
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