My previous reply appears to have been truncated. The "odd text" referred to by Robertsmania has a simple explanation: the synthesis engine is converting the plain text to be synthesised into SSML, and then synthesising it as though it were plain text, so the XML tags of the SSML (less the punctuation) are synthesised. For example, the text "test" might be read as "speak voice name com apple eloquence en G B Rocko test voice speak".

[quote='730789021, Robertsmania, /thread/730789, /profile/Robertsmania'] ...says some very odd text about voice parameters (that is not in the utterance speech text) before it does say the intended speech.[/quote] I'm pretty sure that what's happening is that you're calling the TTS with plain text flagged as plain text, the engine is converting the plain text to SSML, but then it's synthesising it as plain text, so it reads the SSML "" and "" tags. This is still an issue for me in iPadOS 16.7.16.