After doing some more comparisons today with R8Brain Pro's linear phase mode, I gotta say I'm leaning more towards having the Ultra steep mode switched off, rather than on.
I just find it sounds closer to the original than with ultra steep turned on, as having it on seems to make the transients and top end sparkle a bit stronger than was originally present to my ears (resulting in the soundstage seem a teeny bit tighter/smaller)
When using minimal phase mode the difference between ultra on and off is more subtle, but with linear phase mode, the difference between ultra steep on or off is noticeable enough to concern me that having it on isn't such a great idea.
Could anyone else confirm or agree with this difference of having ultra turned on and off and hazard a guess as to why I'm percieving this difference?.
I'm wondering if this has something to do with the way very steep filters can sound unnatural to our hearing and, even though this is way up at the top end of the audible range, it can still have an affect on how we percieve the entire frequency range.
Doing a frequency analysis seems to confirm this for me. The original 48K .wav had the top end frequencies rolloff off up to the maximum 24khz point. But when looking at the 44K linear phase ultra ON, there was no rolloff, it just suddenly cuts dead at the 22K point.
However when looking at the linear phase ultra steep OFF, it displays a similar rolloff to the original 48K source (albiet at a lower level because it rolls off to 22K instead of 24K)
I've upped the images to demonstrate this:
http://www.arksunmusic.com/images/R8Brain_Comp.jpg