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  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),  via analogue,  via the computer CD to the HDP using coaxial, or  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  coaxial or  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  to be behind the analogue option  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  should be very close to the sound of the Tag McLaren CD using coaxial  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  to be one notch down vs. the Tag to HDP over coaxial . 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