What exactly happens while moving "surround" slider in stereo

Hi,

I would like to recreate the surround effect from the stereo expander device, since it is not mono stable (sound will disappear if mixing song in mono). What does this surround algorithm do exactly? Is it just a left/right ms delay? It sounds so good in stereo :slight_smile: It also seems to influence the mono amount of Renoise’s reverb (it reduces it), if it’s after the stereo expander.

Any suggestions which mono stable expander sound very close to the Renoise’s surround?

BTW. the “expand” slider seems to upper the overall stereo volume (at least to my ears), but in mono it sounds the same on or off. So the stereo version will sound subjectively more loud… Just my imagination?