voice speed control for avatars in FULL mode

[noctetemp]

Bug Report / API Issue

Post:

Hi HeyGen team,

I'm implementing voice speed control for avatars in FULL mode using the rate parameter in avatar_persona, but the parameter doesn't seem to have any effect on the actual speech speed.

Implementation Details:

I'm using the LiveAvatar API v1 to create sessions with the following request:

POST https://api.heygen.com/v1/sessions/token

{
"mode": "FULL",
"avatar_id": "ffe5b6c5-e3fe-41dd-99b0-a47a7ed3107d",
"avatar_persona": {
"voice_id": "b95b2b20-5450-4bde-b1ca-8b699465fd82",
"context_id": "<my_context_id>",
"language": "en",
"rate": 0.5
}
}

UI Implementation:

Frontend has a slider control:

• Range: 0.5 to 1.5
• Step: 0.1
• Default: 0.5 (slowest)
• Labels: "Slower (0.5x)", "Normal (1.0x)", "Faster (1.5x)"

Expected Behavior:

• rate: 0.5 → Avatar should speak at half speed (slower)
• rate: 1.0 → Avatar should speak at normal speed
• rate: 1.5 → Avatar should speak 1.5x faster

Actual Behavior:
The avatar speaks at the same speed regardless of the rate value. I've tested with values ranging from 0.5 to 1.5, and there's no noticeable difference in speech speed.

Debugging:

I've confirmed:

• ✅ The rate parameter is correctly sent in the API request (verified via console logs)
• ✅ The API returns a successful response (200 OK)
• ✅ The parameter type is correct (number, not string)
• ✅ Other avatar_persona parameters work correctly (voice_id, language)

Questions:

1. Is the rate parameter officially supported in FULL mode for v1 sessions?
2. Is there a different parameter name or location for controlling speech speed?
3. Are there any specific voices or configurations required for rate to work?
4. Could this be a known issue or limitation?

Environment:

• API: https://api.heygen.com/v1/sessions/token
• Mode: FULL
• SDK: LiveAvatar Web SDK v0.0.10
• Browser: Chrome (latest)

Any guidance would be greatly appreciated! Thank you.