Another element to my discussion above is the different psycho-acoustic models used by the various lossy compressions. From what hello_hello seems to be saying, it seems that AC3 compression first makes AAC compression less effective. This would seem to indicate that the 2 psycho-acoustic models are fighting each other. But remember the DTS is also a lossy compression, just not very much. It is hard to make genuine comparisons. Sources from a DVD or BD will all have been individually compressed from an original lossless master.
So in posts above we have :-
- Master -> DTS -> AAC
- Master -> AC3 -> AAC
- Master -> DTS -> AC3 -> AAC
What we need is
Also we do not know the DTS or AC3 encoders or the settings used to create the commercial media.