Source "Speech"
This source works for Feedback only. It uses the native Windows or macOS text-to-speech engine to speak out any feedback value.
Troubleshooting
If you don’t hear anything, check the Bottom section if unit-wide feedback is currently off. If yes, maybe undefined is enabled but your track is not armed.
Also keep in mind that ReaLearn only resends feedback when it changed. Therefore, the speech source will only say something when the target value actually changes.