Voice activity detection

The Voice activity card under Advanced: a Mode preset for how long the agent waits before it answers, and the five thresholds behind it.

Voice agents

Voice activity detection (VAD) listens to the caller’s audio and marks where speech starts and stops. Every downstream step, transcription, turn detection and the silence timers, works from those marks. The Voice activity card under Advanced sets them with a Mode, how long the agent waits before it answers, and exposes the five thresholds behind it under Advanced.

The Voice activity card with the Mode picker and the Advanced toggle — The Voice activity card.

Configuring it

Open the agent and choose Advanced under Build.
In Voice activity, pick a Mode. To tune one threshold instead, open Advanced in the card and drag its slider or type into its field.
Save.

Modes

A mode is a preset for all five thresholds. Nothing stores the mode itself: the card reads it back from the values, so changing any threshold by hand shows the mode as Custom (The thresholds below no longer match a preset.). An agent that was never tuned reads as Balanced.

Mode	For	Min speech	Min silence	Activation	Prefix padding	End-of-speech
Fast	Short, brisk exchanges: replies as soon as the caller pauses	100 ms	100 ms	0.4	100 ms	0 ms
Balanced	The recommended trade-off between responsiveness and interrupting	100 ms	200 ms	0.5	200 ms	100 ms
Patient	Callers who think mid-sentence: waits longer before replying	200 ms	600 ms	0.6	300 ms	500 ms

Reference

Field	Default	Unit	Range	What it does
Min speech duration	100	ms	100 to 3000, step 100	Shortest sound considered speech. Lower = more eager
Min Silence Duration	200	ms	100 to 3000, step 100	Silence required to treat the user as done speaking
Activation threshold	0.5		0.1 to 0.9, step 0.1	How loud or speech-like audio must be to count as speech. Lower = more sensitive, more false positives
Prefix Padding Duration	200	ms	100 to 3000, step 100	Audio prepended to detected speech, so the first syllable is not cut
End-of-speech timeout	100	ms	0 to 3000, step 100	Silence required before treating the turn as ended

What each one changes

Min speech duration filters clicks and coughs. Raise it if the agent reacts to noise; lower it if it misses “yes” and “no”.
Min Silence Duration is the pause that ends a caller’s speech. Raise it for callers who pause between phrases; lower it for faster replies.
Activation threshold is the sensitivity. Raise it on noisy lines, or turn on noise reduction first and leave it alone.
Prefix Padding Duration keeps the start of words. Rarely needs changing; raise it if transcripts lose first syllables.
End-of-speech timeout is added after the silence before the turn is handed on. Together with Min Silence Duration it sets the floor of the agent’s response time.

Behaviour and limits

Response latency is at least Min Silence Duration plus End-of-speech timeout, plus the model’s own time. With the defaults these two add 300 ms.
Turn detection can delay a turn beyond what VAD decided but never shorten it.
The Max silence timer under Reminders counts time in which VAD heard no speech; a threshold set too high can make a talking caller look silent.
The settings apply to the browser Call test too.

Verify

Start a call under Testing, Call, say short words and long sentences, and watch the transcript: every utterance should appear once, complete, and the agent should answer after a natural pause.

Troubleshooting

The agent answers before I finish. Switch the Mode to Patient, or raise Min Silence Duration in 200 ms steps; then turn on turn detection.
The agent is slow to answer. Switch the Mode to Fast, or lower End-of-speech timeout first, then Min Silence Duration.
Background noise triggers the agent. Enable denoising, then raise Activation threshold by 0.1.