Which directory path to install VST plugins?
You can install VST plugins anywhere on your computer.
Traditionally, as Steinberg created the VST API, the default installation directory for VST plugins was C:/Program Files/Steinberg/VSTplugins. This was because most VST developers assumed that users would be using Steinberg software.
Reapers plugins are installed by default in C:/Program Files/Reaper/Plugins/Plugins.
If you install your VST to the Reaper directory specified above, the next time you start up Reaper they will be recognised and available for use. Alternatively, rescan your VST folder by opening up the plugin selection browser, clicking 'Add' and pressing F5.
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Installing VST Plugins
There are two ways of installing VST plugins. The first is to use the .exe installer and to follow the directions given during the installation process. The other is to drag and drop the .dll file for your VST plugin directly into your VST directory (see the two default paths listed above).
You can specify which directories Reaper scans VST plugins from by going to Options > Preferences > VST. Bear in mind that Reaper can scan multiple directories at once, so in the future, you may find that you thought you placed the .dll files into one folder when in actual fact they are in another. My advice is to only use one directory, something like C:/Program Files/VST Plugins.
If you still have trouble installing your VSTs, I suggest searching on Google for some tutorials or reading the manual for the programs you will use that can host VSTs. Reapers manual can be found at
http://www.reaper.fm/userguide.php
Hope that helps.
Pat