Reverbs, reverbs, reverbs.
They make a mix. So I was intrigued by Savant Audio's most recent release the venerable Qauntum Room Simulator.
It's very very good and so I wanted to do a quick comparison for my own purposes against a long hall - and I chose to download the 30 day Demo of Pernegg Monastry - as I was looking for a compliment to the excellent Karl Bohm Hall.
The conclusion, to put it simply after about 10 minutes of A/Bing, is that whilst the Quantum Room Simulator (QRS) does an excellant job of the later reflections in a room it doesn't really respond AT ALL to the attack of a note.
In the Pernegg Monastry I can hear the bite and attack and breath of the note interacting with the room acoustic (I was using a SWAM flute) whereas in the QRS the sound is flattened out and de-personalised. It becomes a generic flute sound rather than a played and performed line with player dynamics not really exciting the room differently as is the case in MIR's Pernegg.
I'll carry on experimenting but gut reaction plays an important part and the MIR experience is that of a player in a great room - whereas the QRS experience is that of adding some Reverb at mixdown (albeit a particularly good one).