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Sprag builds speech and language models for voice agents. Together with Vobiz, they give your Pipecat agent a phone number: Vobiz carries the call, and Sprag listens, thinks and speaks. Source code: vobiz-ai/Vobiz-Sprag-Pipecat, the complete agent with setup instructions and a call simulator for testing without a phone.

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How it works

A caller phones a Vobiz number. Vobiz streams the call audio over a WebSocket to a Pipecat pipeline, where Sprag Rhythm transcribes it, Symphony writes the reply and Chorus speaks it back to the caller.A caller phones a Vobiz number. Vobiz streams the call audio over a WebSocket to a Pipecat pipeline, where Sprag Rhythm transcribes it, Symphony writes the reply and Chorus speaks it back to the caller.
1

Someone calls your Vobiz number

Vobiz answers and asks your agent what to do. The agent replies with Stream XML, and Vobiz starts streaming the call’s audio to it over a WebSocket.
2

Rhythm hears the caller

Sprag’s speech-to-text model turns the caller’s words into text as they speak. Pipecat detects when they’ve finished their turn.
3

Symphony writes the reply

Sprag’s own model reads the conversation so far and writes what the agent says next.
4

Chorus speaks it on the call

Sprag’s text-to-speech model turns the reply into a natural voice. Vobiz plays it to the caller, and the conversation continues.

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Who does what

Pipecat sits in the middle and runs the conversation. It hands audio from Vobiz to Sprag, and Sprag’s spoken reply back to Vobiz.

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What you need

  • A Vobiz account with a phone number, and your Auth ID and Auth Token.
  • A Sprag API key, from sprag.ai.
  • Python 3.11 or later, and a public HTTPS URL for the agent (a tunnel such as ngrok works while you build).

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Set it up

1

Get the agent

Clone vobiz-ai/Vobiz-Sprag-Pipecat and follow its README to install it and add your Sprag and Vobiz keys.
2

Try it without a phone

Run the repository’s call simulator. It plays the part of Vobiz, asks the agent a question, and saves the agent’s spoken reply so you can listen to it.
3

Give the agent a public URL

Start the agent and expose it over HTTPS, for example with a tunnel. Note the URL.
4

Point your Vobiz number at the agent

Create an application with its Answer URL set to your agent’s /answer address, then attach your number to it.
5

Call your number

The agent greets you, and you can talk to it. To have the agent call someone instead, make a call with the same Answer URL.
Calls are billed to your Vobiz account, and Sprag usage is billed to your Sprag account. Start with your own number.

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Audio quality

Vobiz streams calls as standard phone audio (μ-law at 8 kHz) or as wideband audio (L16 at 16 kHz); see audio formats. Chorus speaks at 24 kHz, and pipecat-vobiz converts its voice to the call’s format, so the agent sounds clear on both.

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Make it yours

  • Personality and greeting: change what the agent says in the repository’s bot.py.
  • Voice: pick another Chorus voice from Sprag’s voice presets.
  • Turn-taking: use Sprag’s own turn detection, described in the pipecat-sprag README.

Example repository

The complete agent and a call simulator

Pipecat

Vobiz with Pipecat

Sprag's Pipecat guide

Sprag’s own guide to pipecat-sprag

Stream XML

How Vobiz streams call audio