But, it is also supposed to play music just fine with a non-MQA DAC. Stuart claims this sounds better than a non-MQA mastered version of the same file into the same DAC because the MQA file contains PCM signal which has been de-blurred, compensating for the original ADC. Please correct me if I am wrong.
You are wrong.
Assume an original 96k recording. If this is blurred at the ADC side (something I don't agree with, but let's assume for the moment...), then this blur lives at the ADC's anti-aliasing filter cut-off, i.e. 48kHz.
An MQA version of this recording
1) applies de-blur (at least, it claims to, but again I do not quite agree ...), which is signal processing around 48kHz.
2) folds the ultrasonic part of the signal (24kHz to 48kHz) down into the least signficant bits of the baseband (0-24kHz).
If you replay the baseband only, i.e. without MQA decoding, your player is not even remotely aware of the ADC's cut-off, since this is at 48kHz. The played only 'sees' up to 24kHz. So how can it profit from the ADC deblurring?
It can't. Simple.
There is more. In order to allow the folding/unfolding of item 2), there are two filters needed during production, and two other filters during decoding. These filters are inter-related, in that their task is to allow lossless folding/unfolding.
These filters insert their own blur, blur which will be net zero in a full encode/decode cycle. That blur will, however, not be zero in the case of an encode-only cycle.
DAC. If Tidal's software can do it, other software, codecs, etc. could easily follow.
As it stands now, it is not 'easy'. There are tons of gear out there that could do this decoding. Look at the LMS eco system, look at the various linux-based low-cost (but excellent, more than excellent!) streaming systems. These are based on open-source,
free software. Look a the various DSP-based active speaker systems out there, commercial and DIY. If MQA have their way, these systems are locked out of it. Unless they pay.
If MQA were really serious about bringing better quality to the people, then they would open-source the decoder.
Since they do not do this, I can only conclude that their aim is to
1) make money in the short term, cynically
2) provide the music industry with a new cow and with a road to DRM.
And yes, I have listened to it. With tracks ripped out of Tidal, unfolded, into the main system (which is purely digital, room-corrected, and based around 96k only, hence MQA-incompatible, unless I ditch the entire caboodle), as well as with an Explorer2 into good headphones.
Quick findings:
1) some of the tracks on Tidal sound dire, regardless their format
2) in some cases the decoded MQA sounds identical to the existing hi-res downloads
3) in a few cases the MQA sounds better than alternative versions; but these are clear cases of better mastering: a bit of eq here, a tad of K-Stereo there, ...
3) shows that MQA can be an incentive to 'do better' (just as HDCD once did). 1) shows that many prefer not to follow this suggestion.