ElevenLabs Voice Synthesis for Bolna Agents

ElevenLabs is Bolna’s default voice synthesizer. The eleven_turbo_v2_5 model delivers natural-sounding English speech with the lowest latency of any ElevenLabs model.

Quick config

"synthesizer": {
  "provider": "elevenlabs",
  "provider_config": {
    "voice": "Nila",
    "voice_id": "V9LCAAi4tTlqe9JadbCo",
    "model": "eleven_turbo_v2_5"
  },
  "stream": true,
  "buffer_size": 250,
  "audio_format": "wav"
}

To use your own ElevenLabs account (for voice cloning or custom voices), connect it at platform.bolna.ai/auth/elevenlabs.

Supported models

Model	Best for
`eleven_turbo_v2_5`	Low-latency English (recommended)
`eleven_flash_v2_5`	Fastest option; slightly lower quality

eleven_turbo_v2_5 is the standard choice for production agents. Use eleven_flash_v2_5 when you need the absolute lowest time-to-first-audio.

Key settings

Setting	Type	Default	Description
`voice`	string	—	Display name of the voice
`voice_id`	string	—	ElevenLabs voice ID (stable; use this, not the name)
`model`	string	—	ElevenLabs model (`eleven_turbo_v2_5` or `eleven_flash_v2_5`)
`stream`	bool	`true`	Enable streaming; always `true` for real-time calls
`buffer_size`	integer	`250`	Characters to buffer before sending first audio chunk
`audio_format`	string	`wav`	Output format — match your telephony provider

buffer_size guidance

buffer_size controls the trade-off between first-word latency and audio smoothness:

100–150 — fastest first word; can sound choppy if ElevenLabs response is slow
250 — balanced default; works well for most agents
400+ — smoothest speech; higher latency to first word

Choosing a voice

ElevenLabs voices are identified by a voice_id. The voice name field is for reference only — Bolna uses voice_id to select the voice. Browse voices in the ElevenLabs Voice Library. Copy the voice ID from the URL or the voice details panel. Example voices:

Voice	voice_id	Accent
Nila	`V9LCAAi4tTlqe9JadbCo`	Neutral American
Rachel	`21m00Tcm4TlvDq8ikWAM`	Neutral American
Adam	`pNInz6obpgDQGcFmaJgB`	Neutral American

For a custom or cloned voice, use the voice_id from your ElevenLabs account. See Clone Voices and Import Voices.

audio_format by telephony provider

Telephony	audio_format
Plivo	`wav`
Exotel	`wav`
Twilio	`mp3` or `wav`
Custom SIP	match codec negotiated

FAQ

Which model should I use — Turbo or Flash?

Use eleven_turbo_v2_5 for most production agents. It has the better quality/latency balance. Use eleven_flash_v2_5 only if your primary constraint is time-to-first-audio and you’ve measured that Turbo is too slow.

How do I find a voice_id?

In the ElevenLabs dashboard, open any voice and look at the URL — the ID is the path component after /voice/. Alternatively, list voices via the ElevenLabs API. Always store the voice_id, not just the name; names can change.

Can I use a cloned voice?

Yes. Clone your voice in ElevenLabs, connect your ElevenLabs account to Bolna, then set voice_id to your cloned voice’s ID. See Clone Voices.

The audio sounds choppy. What should I do?

Increase buffer_size to 350–400. Choppy audio usually means the first audio chunk starts before ElevenLabs has generated enough audio to stream smoothly.

Audio Tab — configure synthesizer in the dashboard
Clone Voices — create a custom voice
Import Voices — use existing ElevenLabs voices
Cartesia — alternative low-latency synthesizer
Latency — how synthesis affects response time

​Quick config

​Supported models

​Key settings

​buffer_size guidance

​Choosing a voice

​audio_format by telephony provider

​FAQ

​Related