Originally Posted by brunk
Lets be clear here. The D18 does have jitter reduction built in. However its the nature of the Sabre chip itself that requires a high quality signal to lock onto so it can perform properly.
Exactly. Many designs use a separate DIR (aka digital audio interface receiver) chip like a Cirrus CS8416 or a Wolfson WM8805 or a TI DIR9001. Those chips are pretty good at locking on to any source, even a poor one.
The D18 (and some other DACs) instead goes with the built in DIR functionality in the ES9018 chip. The drawback - it clearly isn't as good at recovering poor signals. The upside - it leads to lower overall jitter and removes any bottleneck in the signal path by delivering a more pure signal to the ES9018.
Something like a CS8416 (which is very common) uses a phase locked loop to recover a relatively low jitter clock from the incoming signal. Some designers consider that detrimental as they don't want additional processing to the signal. That particular chip results in an "average" jitter spec of 200ps being sent to the DAC, assuming a good design (poorly done, jitter could be far higher). The TI DIR9001 supposedly gets the jitter down to 50ps but is limited to 96kHz. The Wolfson WM8805 does 50ps and goes to 192kHz but is harder to properly implement.
With a most good CD transports, the SPDIF output has a jitter level somewhat higher than any of these numbers. So the DIR helps for the most part. But with a really good transport the native jitter on the output may be lower - for example, my JF Digital HDM-03S has around 100ps jitter on the SPDIF output. So if it sends a signal to a DAC using CS8416, that chip does more harm than good. And then there is the matter of top level USB to SPDIF converters - my Audiophilleo 1 with PurePower spits out an SPDIF signal with jitter in the single digit range. Any of the above mentioned DIR chips is going to mess with that pristine signal and make it worse. Consequently, the D18 shows the biggest improvement when using these sources as compared to my other DACs which have their own DIR chips.
This of course is an overly simplistic way of explaining it, but hopefully it makes a bit of sense. Yulong didn't choose this design just to mess with us and make our transport choices difficult.