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Bolna

Kalpa is a built-in voice provider on Bolna: set an agent’s synthesizer to kalpa.

Bolna is a voice AI platform for phone and web agents, built on an open-source framework. Kalpa is one of its built-in voice providers: set an agent's synthesizer to kalpa and it speaks in Kalpa voices — English, Hindi and code-switched Hinglish from kalpa-tts-1, with no language setting.

Configure the synthesizer

JSON
"synthesizer": {
  "provider": "kalpa",
  "provider_config": {
    "voice": "Arjun",
    "model": "kalpa-tts-1"
  },
  "stream": true,
  "buffer_size": 400
}

On the Bolna platform this is the agent's tools_config.synthesizer; see Bolna's Kalpa guide for setting up agents. provider_config takes:

SettingDefaultNotes
voiceArjunA voice name from GET /v1/voices: the full name (Wren (human-like)) or the part before the parenthesis (Wren), case-insensitive. Bolna looks up the voice's id on the call's first connection.
voice_idnoneA voice id, instead of a name — see Named voices.
modelkalpa-tts-1kalpa-tts-1 for English and Hindi, or kalpa-tts-beta-v0.1 for English only — see Models.
chunk_length_schedule[50, 80, 120, 150]Buffered-character thresholds at which Kalpa starts rendering each part of a reply while the rest is still arriving.

temperature, acoustic_temperature and audio_quality are optional; leave them out to use Kalpa's defaults (Generation parameters). stream and buffer_size are Bolna's own synthesizer settings: keep stream: true for live calls, so speech streams as described below.

How it streams

Each call holds one connection to the streaming WebSocket WSS /v1/tts/{voice_id}/stream. Bolna forwards the LLM's reply as it is written and flushes at its end. Once the buffered text crosses the next chunk_length_schedule threshold at a sentence boundary, that part starts rendering, so the caller hears the reply before the LLM has finished it. When the caller interrupts, Bolna cancels the response and reuses the connection for the next turn.

Kalpa streams 24 kHz audio. Bolna converts it to 8 kHz mu-law for phone calls and plays it unchanged in web calls.

Self-hosting

To run the open-source framework yourself, create an API key at kalpalabs.ai/dashboard/keys and set it as KALPA_API_KEY in the Bolna server's environment.

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