Configuring Rack Modules Manually

Add Empty Module

Double-click in the empty area of the rack to add an empty module based on the currently selected host. By default this is the preferred Audio Engine, unless some other host is selected on the tabs over the rack area.

If you want to use a Drone, Drop a yet unused one from the Rack Module Library, which will also add an empty module.

Load Plug-in

Hover over the Plug-in Button and click on the double-arrow icon to select an audio plug-in to load. The editor of the plug-in will open, unless you are using a Drone. In the latter case you need to switch to the DAW and open the plug-in editor there. Synfire can't force the DAW to do that for you, unfortunately.

Configure the plug-in's sounds to your liking.

Select Device Description

Unless the module is for an audio effect, it needs a Device Description, so Synfire can know what kind of sound the plug-in is providing. Pick one from the menu or create a new one as explained here.

Save a Preset

Once you have set up a rack module that is likely useful on other occasions, you should save it as a preset. This will make it appear in the Rack Module Library on the sidebar, from where you can conveniently drop it on future racks and instruments, so you won't have to configure it again.