Thanks to
@andreasmaaan for digging up the output impedances of the DACs. I have sent an email to Goldpoint to enquire about the behavior of the SA2X-I when set to "no attenuation". I will report back when I hear something.
For me this thread has been very interesting, because it has raised a number of fundamental issues, as I was trying to get to the bottom of why the issue of "I hear differences" and "no you don't" is such a contentious one.
One issue seems to be the question of scope of experiment. When a DAC is being measured with an analyzer these two pieces of equipment comprise the scope of the experiment. The DAC's output is connected to the high impedance input of the analyzer using a relatively short cable with limited capacitance. Unfortunately an analyzer does not have ears. So when it comes to listening to music, the scope of the experiment changes fundamentally. We are now dealing with a complete hifi chain, a room, ears, a nervous system and a conscious person interpreting the stimuli and deducing conclusions. While I find the measurements conducted in this forum extremely valuable (I really do), I am even more interested in the transferability of the conclusions drawn from the measurements to a live listening environment. This is not a trivial process, as described
here.
In a hifi setup similar conditions to the analyzer experiment may apply, if the DAC is connected to a preamp with high input impedance using similarly short cables. If the DAC is connected to a monoblock amp using long cables, things become fundamentally different, especially if the DAC should have a high output impedance such as Chord DAVE in single ended mode. Even more so if a passive attenuator is used in the path.
So "all DACs that measure well sound the same" seems to be a statement that holds true only under certain conditions. While the behaviour of a DAC connected to an analyzer seems to be quite well defined, the picture becomes less clear as the DAC is introduced into a complete system and starts to interact with cables, inputs, power supplies etc. The concept of impedance architecture has certainly hit home with me and I will look at my friend's and my setup regarding the influence of impedance. I also connect the dCS Rossini directly to two Neukomm PA18 Monos with around 5m of Prefer PMK-206 cable. Luckily I don't need a passive attenuator, not even the attenuator of the dCS. I can run the dCS at full volume and adjust the volume directly with the Neukomm Monos' built in attenuation circuit. So one less element to worry about.
A valuable piece of information from my perspective would be a set of system architecture recommendations, under which the premise of "all DACs that measure well sound the same" actually holds true. In these conditions the conclusions from the measurements could then actually be transferred. Maybe one could also measure the DACs using different lengths of cables to determine if the output impedance of the DAC interacts in a significant way with the cabling. I was asked in one of the posts to name one or two additional measures for the test sequence. This could be one of them.
The second area that went through my mind was the one of digital filters. Most DACs these days contain several digital filters. They measure different, so they will likely also sound different. All of these filters are compromises, tuned to optimal frequency, phase or transient reponse or a mixture of these and other parameters. None of them is accurate, as no absolutely accurate transfer function exists when transferring a bandwidth limited digital signal to analogue.
Studies show that in order to achieve spatial sound localisation resolution humans (and other mammals) can achieve, a
temporal detection accuracy of a few microseconds is necessary (this is apparently independent of our frequency limited hearing ability). In my view this begs the question, how different digital filter characteristics influence our ability to detect say 3 dimensional space in a recording. In our very subjective DAC comparisons the easiest way for me to differentiate was to judge the proportions of the 3 dimensional space of the recording. One explanation might be that the filters of the two DACs had differing phase errors across the audible spectrum and hence different ability to accurately provide the timing of spatial cues from which to derive a sense of space. Some DACs generated a deeper and more clearly defined 3 dimensional reproduction of opera singers moving about on stage. Call this audiophool nonsense if you wish. Anyway, I think it might be worth to look at phase errors across the audible spectrum as an additional measurement. I would certainly be interested to hear other people's thoughts about this.
@Frank Dernie thanks for your comments re. filters above.
So, has this thread gone "down the gutter" - for me definitely not. Quite the contrary.