>>There have been lots of efforts to eliminate jitter in common players, and nobody mentioned outstanding sound with these, at least not a characteristic one AFAIK.
I thought it was the opposite? Lot of people upgraded their clocks to low jitter ones and reported substantial changes in sound. I myself did one such modification and was quite happy with the results. But other than clock upgrade, where benefits depend on particular chips used and their configuration, the actual real reclocking that yields guaranteed low jitter at the D/A chip itself is a fairly complex proposition since you have to build a custom PLL from basic parts and have an elastic memory buffer to allow asynchronous reading. I have one such DIY DAC (March Heilingers at al.) and the sound is just marvellous. Modded SACD775 is not bad but this reclocked Redbook was better. But from what I know very few designs of this type exist - I am aware of two DIY designs and in commercial world I heard Wadia was doing that. Anyhow these asynchronous sample rate converters achieve jitter reduction in a different way - first they upsample to a very high frequency (tens of MHz I think) and then they downsample to target frequency. Note that these chips can also DOWNSAMPLE or even do 1:1 (i.e. 44 to 44 kHz), still with same low jitter benefits. Typically jitter reduction in all these digital audio chips (not just sample rate converters) starts only above audio range, while many people claim that the jitter is much more dangerous at low frequencies. By using very high intermediate frequency they are somehow able to achieve similar jitter rejection curves as you can see with real reclockers (which start rejecting it even below audio range, i.e. at several Hz). I really need to read the theory behind it. It would be very interesting to try different sample rates as that would give some clue as to what makes them sound better (or different).
>> Are you alluding to the Audio Note concept? Why did you get away from your former filterless DAC? Actually this one would be heavily exposed to aliasing, right? But I guess it's much less harmful than one thinks because the music on CD is low-pass filtered before A/D conversion anyway... or what is your experience in this concern?
Yes, most people mention Audio Note in this respect. My concern with portable DAC was power consumption so I had to omit digital filter. And I still do, but I have added an analog filter now. And yes, if you look at the signal in time or frequency domain, you can definitely see artifacts in the ultrasonic range since obviously the 2 pole analog filter is not all that steep. However it sounds good regardless - which is probably Audio Note's selling point. One concern here is that non-attenuated artifacts can damage some speakers and amplifiers. I remember reading that SACD uses 50kHz or so filters to get rid of their own artifacts (as their process-related noise rises dramatically with frequency) beucase of these concerns. So I added analog filter for a piece of mind, although anything sold today and advertised for 24/96 or more has to handle wider than audio bandwidth anyway.