Vocov is a VSTi Vocoder.
Internal 2OSC synth is used for carrier.
you can use .wav files to modulator audio, or you can use other audio track on your host app by VOCOVCapture.dll ( used as a VST Effect) . VOCOV will automatically connect to VOCOVCapture.

http://www.g200kg.com/archives/software_vocov_e.html
http://www.g200kg.com/software/vocov08.zip