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
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.
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?
Hi, we’re seeing a similar issue with google/gemini-3.8-flash-tts through OpenRouter.
Our setup:
Default voice: Alnilam
One request containing a 715-word Bulgarian script
One continuous response, approximately 5 minutes 16 seconds
No style override or speed/pitch adjustments
Input includes short pause tags and Bulgarian syllable-stress marks
The voice sounds noticeably different between passages around 01:04 and 01:12 in the original recording—almost like another person speaking. Both passages come from the same uninterrupted API response, so this isn’t a mismatch between separately generated clips.
We switched from separate scene recordings to one full-script request specifically to improve consistency, but the issue persists.
Is there a recommended workaround for maintaining the same prebuilt voice throughout a longer single-speaker recording?
I got the same problem, one single voice in 10 mins drift other voice around 5 times, it is so annoyed that I can not use gemini flash 3.8 tts for my project like storytelling with one signature voice. I really want to know when the consistency issue was fixed, how i can receive any update about this update or other alternative method for my case, 1 voice with high volume, vibrant and consistency, pls let me know asap thank you in advance!
We see the same voice-consistency problem on gemini-3.8-live (Live API, prebuilt voice Kore). Within a single session, an occasional reply comes out in a clearly different, lower male-sounding voice, then the next reply returns to Kore. In our controlled tests it is rare without video (about 1 in 1,700 replies), roughly 13× more frequent with camera frames streamed into the session, and it never happened on gemini-2.5-flash-native-audio. No reconnects or context compression were involved. We have a minimal reproduction with the bare SDK and can share clips. Is the voice-consistency fix you’re working on for 3.8-flash-tts expected to cover the Live model too?
Following up on our post above: the full write-up for gemini-3.8-live is now in its own topic, with measurements, a minimal bare-SDK reproduction script and pitch plots:
In short, it is the same kind of voice-consistency shift: with prebuilt voice Kore, whole replies come out in one consistent male-sounding voice, in about 2-4% of replies when video frames are streamed into the session and a child or a woman is speaking (about 0.1% audio-only), and in none (0 of 526) on gemini-2.5-flash-native-audio-latest with the same input. We can share WAV samples by direct message.
I would consider Gemini 3.8 Flash TTS as one of the biggest disappointments in AI. For the cost, its the best sounding and performing. But it parks in a handicapped zone. The drifting. It even interprets texts, add words, hallucinates. This isn’t your typical TTS model. I dare to even call it that. Switching to Elevenlabs is a no brainer. Even the el cheapo Kokoro is at least far more reliable than Gemini. You would think Google would be on top of this but it reminds me of Microsoft. They were notorious for leaving things broken while pretending to fix it. As my dad always said, you can’t fix stupid.
I’m experiencing severe voice drift and voice inconsistency with Gemini 3.8 TTS, even when using Google’s official preset voices.
Even when I use the exact same preset voice, identical API parameters, and the exact same text, repeated generations can produce completely different-sounding voices. The inconsistency is unpredictable and extremely frustrating.
The problem becomes even worse with long-form text. Voice drift happens frequently during a single generation, making it nearly impossible to maintain a consistent voice throughout a long narration. Sometimes, a female voice suddenly turns into a male voice in the middle of the audio!
What’s particularly frustrating is that Gemini 3.8 TTS is actually excellent in terms of naturalness, audio quality, and pricing. It has enormous potential. However, this bizarre and severe voice consistency issue makes it practically unusable for real-world production.
Please prioritize fixing this bug as soon as possible!
Frankly, I find it hard to believe that proper quality testing was conducted before this model was released. This is such a fundamental and easily noticeable problem that I’m genuinely shocked it wasn’t caught during internal testing.
How could such an obvious and critical issue make it into a public release?
I really hope the engineering team takes this seriously and provides a fix soon. Voice consistency is not an optional feature for a TTS model — it is one of the most basic requirements.