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Background audio runs continuously during a conversation. A thinking sound runs while tools are working, and a spoken filler is generated speech. Try each separately before combining them.

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Add a preset

Keep a dict-based voice_config as in the tool example, and add:
Restart the server and start a new session in /voice. You should hear low room tone with typing, including while neither side is speaking. Use the playground’s local volume control to adjust what you hear. Available presets are office, call-center, cafe, city, and typing. Tracks are fetched on first use from the Timbal CDN, verified against a pinned checksum, and cached locally. volume defaults to 0.3 and accepts values from zero to one.

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Use your own track

Set source to an existing server-side audio file instead of a preset. Prefer a clean loop with no intelligible speech; audio leaking through a speaker into the microphone can otherwise become a false transcript. Keep the track quiet enough that the caller can understand the assistant. The source path must exist when the config validates. A client cannot send an arbitrary file path through the configuration hello. Operator defaults use TIMBAL_VOICE_AMBIENT_SOURCE and TIMBAL_VOICE_AMBIENT_VOLUME.

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Transport limits

The current playground fetches /voice/ambience/current and plays the loop in the browser. Its ambience picker and volume controls affect local playback. This repository’s built-in media transports do not mix ambience into outgoing WebRTC, LiveKit, Twilio, or Telnyx tracks, and the server recording does not include this browser audio. A browser can play the track alongside received media, but a phone caller needs ambience mixing in the media host. Declaring ambient alone does not add a phone-call background track. A custom client needs access to the ambience asset endpoint or its own audio asset. Continue to Turn-taking and interruptions.