I have that specific preset in my both of my Eventide's. Way cool effect.

I'm not familiar with eventide, could you post a link with the specific model please?

thnks in advance

eventide clockworks is a manufacturer of digital FX gear of long standing in pro studios world wide... known especially for there "harmonizer" type effects... one of the things that contributed to that sound was the way it interacts with the room... big echoey things... and since they got anal about the ratios of length to width and highth it could often tend to ring in a key...(Ab cathedral?) so try setting up a huge reverb and if you can get it to ring on pitches of say open 4th's ....

A search arrouund here or on the web will give you plenty of info on Eventide. The specific gregorian chant preset may not be in every Eventide, but any of the units that can do 8-voices of pitchshifting, can programmed to do hat effect such as the older GTR4000/DSP4000/DSP4500/DSP7000/DSP7500/Orville and the newer H7600 or any of the H8000 variants.