Yes, it uses the browser’s TTS.
When I rebuilt my first main application in Saola (Built with Saola), I tried using audio files - but kept getting a slight delay between the interaction on the tiles and the playback of audio. Also the basic 100 square has a corresponding number if audio files. I’ve since updated that project to use TTS as well which means you get speech for even larger numbers.
The original clock application also had .mp3 audio speech but I had been looking at TTS after reading one of the Active Presenter posts.
The default speech in the desktop browsers was not great but I discovered that Chrome (and iPad) provides access to much higher quality voices and was very impressed by the pronunciation of the UK voices that I decided to try TTS.
Both Plethos and TickTock use the same functions. They first check a querystring value that allows the teacher /student to specify a voice (if available)*1:
https://activities.interaktiv.co.uk/ticktock/?voice=Google%20UK%20English%20Female
If not, they then try and use the default Male Chrome voice and if that fails, they look for the first en-GB voice.
If all that fails, it then picks the first voice in the browser’s available voice list.
Ideally, these projects will have some simple voice panel that will allow the user to change voice / pitch / rate on screen.
Also, by using TTS, I want to see if these or future projects can be made multilingual.
*1 the link will change TickTock’s default voice to Google’s UK Female if that voice is available on your system.