Make sure you have Carla + the Carla bridge packages installed. These can be installed via the Ubuntu Studio Backports PPA*. To add this type:
sudo add-apt-repository ppa:ubuntustudio-ppa/backports
sudo apt update
sudo apt full-upgrade
sudo apt install carla
sudo apt install carla-bridge-win32
sudo apt install carla-bridge-win64
Make sure WINE** is installed so that we can open the Windows Spitfire Audio Downloader App:
sudo dpkg --add-architecture i386
wget -nc https://dl.winehq.org/wine-builds/winehq.key
sudo apt-key add winehq.key
sudo apt-add-repository 'deb https://dl.winehq.org/wine-builds/ubuntu/ bionic main'
sudo apt install --install-recommends winehq-stable
Install Windows Spitfire Audio App from: https://www.spitfireaudio.com/info/library-manager/
Run installer with Wine and follow prompts to setup paths for VSTs and download the instruments you want.
In Carla go to the Main settings menu, check ‘Enable experimental features’, then in the experimental tab, make sure ‘Enable plugin bridges’ and ‘Enable Wine bridges’ are checked.
In the ‘Paths’ tab select VST from the drop down menu and add the correct path to the Spitfire VSTs
Finally click ‘Add Plugin’ then‘Refresh’ (making sure windows 32 and windows 64 is selected), and Labs should appear.
* More info here: https://help.ubuntu.com/community/UbuntuStudio/BackportsPPA
** More info here: https://wiki.winehq.org/Ubuntu