This feature allows you to use Virtual Studio Technology (VST) DLL plugins to apply effects to the audio you are working with in WavePad. To use this feature, select Effects menu -> VST Plugins. In case you have not specified at least one path for the VST plugins, you will be asked if you want to do so. If you click on 'Yes' a window will appear and you can browse for the directory on your computer that contains VST plugins. You can also specify the path(s) for you VST plugins by choosing Options under the Tools menu and navigating to the VSTs tab - note that the plugins must be DLL files! Next, click the "OK" button to see the selected VST plugin effect window.
Note: VST3 plugins are not yet supported on WavePad.
Once you have specified a directory name, you should see a list of VST plugin names appear in front of the label 'Effect' in the window. In the VST plugin effect window, you can change the parameters provided by the plugin. You can hear the preview of the audio while adjusting the parameters. Check "Bypass VST" if you want to hear the preview without the plugin effects. You can also select the desired preset from the pull-down list provided by the VST. Otherwise, you can save your parameter settings in a file (.fxp or .fxb format) and later you can load the settings from the file. This will enable you to change the VST parameters without manually handling them each time. Press the "Apply Effect" button to apply the effect to the selected audio.
Also please visit http://www.kvraudio.com, which is a comprehensive information resource for all types of plugins, including VST and DirectX plugins.
To see a list of recommended free VST plugins for WavePad, visit http://www.nch.com.au/wavepad/free-vst-plugins.html.