Almost 10 years ago I released the Revelation One filter, a serious improvement over Meridian’s apodizing filter (which they are still using today and on which the time correcting aspect of MQA is based). But even my RevOne filter turned out to have some drawbacks. Although it has less issues than Meridian’s apodizing filter, it still has the following issues that all (upsample) filters seem to share:
1) Muddying the lows.
2) Adding artificial spatiality.
3) Changing the tonal quality of the sound (voices, instruments, etc).