Turn-taking and barge-in

The hardest part of a voice conversation isn’t the answer. It’s knowing when to give it. Answer too soon and the agent cuts people off mid-thought. Wait too long and every reply feels slow. This page explains how Fonoster decides when the caller has finished, how your agent answers quickly without jumping in, and what happens when the caller talks over the agent. Fonoster does all of this for you. Your agent never listens for silence itself.

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Endpointing versus end of thought

Most voice systems use endpointing: wait for a fixed stretch of silence, then reply. It’s simple, and it’s wrong in both directions. People pause mid-sentence to think (“My account number is… let me find it…”), and a fixed timer treats that pause as the end. People also finish a short answer (“Yes.”) and then wait, and the same timer makes them sit through the full silence. Fonoster estimates end of thought instead. For each caller turn it keeps a running estimate, from 0 to 1, of how likely it is that the caller has finished. The estimate rises during silence after a complete sentence and falls the moment the caller speaks again. It uses the caller’s audio, the transcript so far, and whether the agent is talking.

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Three moments in a turn

The estimate turns into three moments that your agent reacts to: Preparing early is how the agent answers fast without answering early. The model starts writing while the caller might still be talking, but nothing plays until the turn has really ended. When the caller was only pausing, the work is dropped and the caller never knows. A turn can have several false alarms before it ends. Every turn ends exactly once.

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Patience

Patience is the one setting that changes the timing. It has three levels: At low and normal, Autopilot prepares replies at “likely ended”. When the agent’s own conversationSettings.patience is high, it waits for “ended”, because a patient agent is one that shouldn’t guess. High patience that comes only from the application’s speech settings stretches the wait but doesn’t stop early preparation. Patience also adapts within a call. Each time a caller resumes after a false alarm, Fonoster becomes a little more patient with that caller, up to 1.6 times the agent’s level. It never becomes less patient than you asked for. After three false alarms in one call, Autopilot also stops preparing replies early for the rest of that call. None of this carries over: every call starts from the agent’s setting. You set patience in the agent’s conversationSettings.patience, or in the application’s speech.patience. The agent’s setting wins unless it’s normal; then the application’s speech.patience applies. See Build an Autopilot agent and Autopilot configuration.

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Barge-in

Barge-in is when the caller talks over the agent. Your agent’s allowUserBargeIn setting (Let callers interrupt in the dashboard) decides what happens:

• On (default). The agent stops talking as soon as the caller cuts in, and listens.
• Off. The agent doesn’t stop for the caller. When the caller’s turn ends, the agent answers what they said.

When the agent is interrupted, the model remembers only the part the caller actually heard. If the agent was halfway through a price when the caller cut in, the model knows the caller didn’t hear the price, and it doesn’t assume they did. This is why prompts for voice should put the important part of a reply first. Some messages always play to the end, whatever the setting: the goodbye message before a hang-up, and the transfer message before a transfer.

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Backchannels

Short acknowledgments like “uh-huh” or “right” aren’t interruptions. The caller is listening, not taking the turn. The default detector (baseline) treats any speech over the agent as speech, so on an agent with barge-in on, an “uh-huh” can stop it.

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Silence and idle calls

Turn-taking decides when a turn ends. Idle handling decides what to do when no turn starts at all. The idle clock runs only while the agent is listening. After idleOptions.timeout of silence, the agent says the idle message, such as “Are you still there?”. When the caller stays silent for the last of idleOptions.maxTimeoutCount timeouts, the agent says the goodbye message and hangs up. A burst of line noise can look like the start of a turn. If no words follow within 10 seconds, that turn ends empty. The agent doesn’t answer it, and it doesn’t reset the idle count, so a silent caller still gets the goodbye on time.

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The turn detector

The part that produces the estimate is called the turn detector. Fonoster ships a default detector based on voice activity, transcripts and a silence timer, and supports others, such as a speech recognizer that reports the end of a turn itself. Agents created in the dashboard, the API or the CLI use the default detector. You can’t choose a detector per agent. Your agent’s code and settings are the same whichever detector runs. If you run your own install, see Tune turn-taking and audio.

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Reading turns in the call record

Every call record keeps the turn decisions for the call, and labels each turn: Many cut-off labels suggest more patience. Many slow labels suggest less, or a slow model or tool.

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Next steps