The native TTS is not great. It doesn't sound like Siri — it's much robotic.

It can sound significantly better but there’s a couple hoops you have to jump through - and even then it’s decent, but not the same as Siri.

You need the user to download ‘enhanced’ or ‘premium’ voices in the settings app. (Settings -> Accessibility-> Spoken Content -> Voices -> [Language of choice] -> [Voice of choice] -> Enhanced or Premium)

In the app you have to search for the enhanced or premium voices when doing TTS.

Heres an Objective C example, I’m sure there’s an easier way to write it in Swift. https://github.com/osmandapp/OsmAnd-iOS/pull/1156/commits/0b...

I’m not sure if you’ll find this acceptable from a UX point of view but there’s an option to play with if you’d like.

Yeah, I use a premium voice but was still disappointed when we added the feature to my reader app. I decided to leave it in the app since we'd already built it at that point, but it's kind of a bummer since obviously they could use Siri-level TTS if they wanted to.