We’re running a voicebot product built on top of the OpenAI Realtime API (currently using gpt-realtime-mini). We have noticed that the Ballad voice is changing tone mid-conversation or between calls — shifting from its expected calm/warm style to something more neutral or flat, without any change on our end.
What we’re seeing:
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Same system prompt, same session config
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Ballad sounds noticeably different across calls — sometimes warm/expressive, sometimes flat
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Other voices (e.g. Alloy, Echo) seem more consistent in the same setup
Setup:
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Realtime API via SIP integration
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Sessions initiated programmatically with identical parameters
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No changes to
voice,instructions, orturn_detectionconfig between sessions
Questions:
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Has anyone else noticed tone/personality drift in the Ballad voice specifically?
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Is there any known variability in voice characteristics tied to model updates or infrastructure changes on OpenAI’s side?
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Is there a way to “anchor” voice personality more reliably through the system prompt?
We’re considering removing Ballad from our available voice options for this use case, but wanted to check if this is a known issue or something with a workaround before doing so.
Any input appreciated.