How can I install vst_perfect_declipper.dll in SONAR X1 PRODUCER?

if you have already installed the plug in, put the DLL in the vst plug ins folder and make sure to scan that folder (depending on which version you installed 32 / 64 bit).

That's the 32-bit VST2 version of the plugin. Installation consists of simply copying the DLL into c:\program files\cakewalk\vstplugins (or an alternate location if you have a special place for 32-bit plugins) and running a scan. SONAR should automatically bridge it, but not having used this plugin I cannot guarantee that it's compatible with bitbridge. If you're running 64-bit SONAR, I'd suggest going back to the site and grabbing the 64-bit version of the plugin. That might avoid some issues.

Hi, and welcome to this forum.
Chuck is right. This plugin is a single .dll file, and can be copied to your plugin folder.
Depending whether you have 32 or 64 bit SONAR installed, it can be copied to C:\Program Files\Cakewalk\VstPlugins for 64 bit, and C:\Program Files (x86)\Cakewalk\VstPlugins for 32 bit (by default).
If you do not have automatic background vst scan set in Preferences, you can right click in the fx bin, and on top there is a manage plugins option. Go there and click scan vst plugins.
Hope it helps.
All the best.