Hi. There is an issue where it is not currently possible to set a 4in/2out routing for a channel (where 3/4 inputs are for side chain) when using Fab Filter Pro L2. Pro-L 2 supports surround processing, when you create it on a 4-channel track, Reaper asks it if it can work with four channels I/O. And Pro-L 2 can do this and creates itself in a quad configuration, so it actually has 8 channels of input and 4 channels of output.
I've already reached out to Fab Filter support and someone else in the FF forum could not get it to work:
https://www.fabfilter.com/forum/3113...put-and-reaper
Fab filter said this:
"Over the past week, we've been in close contact with Justin Frankel from Reaper about this and it turns out that it's due to the way you work with side chains in Reaper. As you know, to use a side chain with a stereo plugin, you have to create a four-channel track and route the side chain data to channel 3/4.
However, because Pro-L 2 also supports surround processing, when you create it on a 4-channel track, Reaper asks it if it can work with four channels I/O. And Pro-L 2 can do this and creates itself in a quad configuration, so it actually has 8 channels of input and 4 channels of output. Of course that's not going to work.
Note that there is a bug in the currently shipping version of Reaper that causes it to end up in a LCR config with 6/3 I/O.
As we see it, Reaper needs to provide a way to indicate how many channels you want in a plugin that can support surround formats, so the user can choose whether to create plugin with e.g. a 4 in/2 out config, or a true quad config (L/R/Ls/Rs) when using a 4-channel track.
Unfortunately Justin believes that *we* should change Pro-L 2 to add some way to fix it to a particular channel configuration. We don't want to do that because it would only be needed in Reaper; all other hosts work differently with side chains so the problem doesn't exist there. So that's more or less where we are now and I haven't succeeded in convincing him of our view. I'm sorry I don't have better news at the moment!
Maybe it would help if you would email him as well to explain your situation? "
I really want this to get sorted because this is only an issue in Reaper and no other DAW. What can we do! I've already emailed Justin to show my concern..... not sure if FF will want to change Pro L2 so it will work with how Reaper currently handles multichannel audio.