FabFilter User Forum
Pro Q4 - Different channel routing between VST3 and CLAP version
Hi,
I'm mainly using the CLAP version of your plugins and noticed that it behaves differently than the VST3 version in terms of channel routing.
If there are 4 Channels on a track, the VST3 will map 3/4 to the sidechain inputs, while the CLAP creates new main ins and outs and doesn't use the sidechain.
If I add two more channels, the VST3 still goes with a stereo configuration with 5/6 being unmapped while the CLAP now has 12 channels in total and still doesn't use the sidechain.
If this is intentional it would be great to have an option in the plugin to make the CLAP version default to stereo mode.
Dr.Gunjah — Sep 11, 2025
Hi Dr Gunjah,
The channel configuration depends on what is being recalled by the host. In most cases for a stereo track the host will recall a channel layout with 2 inputs, 2 side-chain inputs and 2 outputs. Some hosts like Reaper offer some more flexibility when it comes to channel routing, but this also means that it's a bit less structured with the default channel layouts, as you have already noticed.
We offer all sorts of layouts from mono up to 9.1.6 and everything in between. These are the same for all plug-in formats. What layout is being used exactly depends on what the host is requesting. I'm afraid we don't have any control over that I'm afraid.
Hi Ralph,
The channel config for VST3 with 4 channels is: Stereo in L, Stereo in R, Stereo Side Chain In L, Stereo Side Chain In R, Stereo Out L, Stereo Out R
For Clap it's: Main In 1-4, Side Chain In 1-4, Main Out 1-4.
As far as I can tell Reaper "offers" track channels 1-4 in both cases, but Q4 exposes different connectors for CLAP and VST3. Correct me if I'm wrong, but it looks like the rows in the routing matrix are the channels that Reaper offers, while the columns are what Q4 makes out of it.
For plugins with fixed channel config the columns never change, no matter how many channels are added.
After some testing I've noticed that if I change VST3 bus size from auto to a certain number, Q4 seems to "predict" the most relevant format like "quadro" or "5.1". Which is a nice idea, until it's not doing what I want. So the VST3 format or Reapers implementation of it seems to have some "default stereo mode" builtin that prevents this. Imo it should be a setting in the plugin like "default to stereo mode".
Just one scenario where this can be an issue: Add Q4 to a 2 channel track, eq something. Later, you add a sidechain to this track, so you send something to 3/4. Now Q4 will automatically adapt in the background and process channels 3/4 which makes no sense obviously. You have to know or notice it, go to Q4 and manually change the routing config.