With respect, if you start with vague claims under investigation, you are likely to end up with vague conclusions. I recommend that you distill the claims into a testable hypothesis that then can be unambiguously proved or disproved. My personal interest would be to measure the level of artefacts introduced by bandsplitting and determine if they are at a level likely to be inaudible. And in non-MQA DAC playback, determining if the extra HF noise is audible (I think I have heard this).
As far as the MQA filter issue is concerned, it's not "freewheeling" phenomena that you captured (this is a new thing that you should be credited with first discovering
). What I am describing is that some MQA DACs, when receiving LPCM music after having processed an MQA piece, retain the MQA-specific reconstruction filter (perhaps until they are turned off), instead of switching to the filter the user has picked for non-MQA content. I have read that DAC makers were being encouraged by MQA to do this as it aids in gapless playback of playlists that include MQA and non-MQA material.
The specific tests I do then give specific results. By doing a variety I can start to 'box in' the claims and find any contradictions, etc. Given a set of vague and sweeping claims, internal contradictions become useful as way to find that at least *some* of the claims must be shakey.
You can't have your kayak and heat it...
The 'bumps' show some of the artifacts. This alters in the output, but remains, and seems *very* unlikely to be a common feature of the source material prior to MQA encoding.
One of the reasons I'm looking at making (linear) corrections to the added dispersion, etc, is to help untangle linear changes from non-linear or added-subracted artifacts that are harder to detect because the dispersion, etc, make a simple 'sample-by-sample-diff' fail to show the nonlinear differences. (I'm also looking at other ways of doing that.) However like steganography, that can be a long game.
Your pointing out what some DACs do, is useful. I will try to look at that. However when I play the 'tailed' files the MQA led does go out during the tail being played. So it does detect - after a delay - that the material isn't MQA. But as you indicate that doesn't mean the decoder isn't still applying at at least some MQA changes. So thanks for pointing out the other DACs. I'll have a look at this for the Explorer 2. It would be very handy for investigation if it will leave the decoder on for long periods.
MQA wanting this for gapless reasons seems weird to me. It impies non-MQA files will get 'faked' alterations applied. If I were a user I'd not be delighted by that. Can you list some of the DACs that do this and point me at any details?
I'll be doing more tests on the Explorer 2 anyway. e.g. want to check what happens when the internal gain is wound down 6dB. As it stands it can't cope with 'overs' very well so want to see if that fixes the limitation.
And - as always - I encourage you and others to do your own tests to investigate. e.g. if someone is using roon to decode MQA see if you can capture the output or apply changes to it to undo the dispersion, etc. Given what I've seen thus far I suspect that using even a fairly 'budget' ADC like the Scarlett 2i2 3rd Gen would yeild useful data. (I have one of these and it works fairly well. Just not in the ADC1 class - but of course, only a fraction of the price!)