Gemini 3.8 TTS voice consistency issue

Gemini API
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1

Hello,

I’m having a problem with gemini 3.8 TTS generation. I noticed it drifts much less than previous models but it also randomly switches voice tone.
I tested without any instruction and a google default voice, created multiple 2 to 7 min audio and in almost all I can hear at least one abrupt change in tone, like if it’s a different voice.

This always happens after a phrase change, so I tried on AI studio to replace periods with commas in order to avoid the issue, but then it drifts a lot and “crashes” at some point, meaning when voice drifts too much it refreshes, probably a safeguard (though I tried this only once).

Then, I tried with multi-speaker mode, one narrator, splitting in groups of 1, 2, 4, 16 phrases. Each still causes a random switch in tone.

Do you have any idea on how to fix the issue? Unfortunately this makes it unusable for my use case

2

Adding to the above, I also just noticed a voice switch happening within a phrase, and the model adding a word not existing in the text (the second “molecule”, from the example) right at the switch point.

3

Hello @Thomas_Rossi_Mel ,

Thanks for the detailed report and for sharing the audio sample. We have shared this with the engineering team and are looking into the voice consistency shift on longer audio generations. Could you also share which voice name you selected and the full text prompt used for that sample (and your Project ID via direct message) so we can attach them to the investigation?