As far as I understand it Synth V & Synthesizer V are one and the same. It's usually referred to Synth V on other sites like Wiki etc.

If you are referring to the two versions for the voices, the standard voice is often known as Lite, sometimes free. The A.I. version is the full version.

You will need to be online to use the voices as they refer back to the Synthesizer V site in real time to access the database.