It would use RT cores by default, but if they weren't available or in use (EG: running a game with Ray Tracing) it could fall back to the older CUDA

That's also why they split it out into two products now

"Nvidia Broadcast" is their "you bought an RTX GPU so here's a shiny toy"

And "RTX Voice" for people with GPU's dating back to the Geforce 400 series that only does it via CUDA