> For a complete page index, fetch https://docs.synthflow.ai/llms.txt. For full documentation content, fetch https://docs.synthflow.ai/llms-full.txt.

# Call Configuration

> Configure call behavior, ring timing, silence handling, voicemail, and audio controls for Synthflow voice agents.

![Call Configuration panel in the agent editor showing Noise Cancellation, Ring Duration, Limit Call Duration, Leave a Voicemail, and the Advanced Settings section](https://storage.googleapis.com/granular-changelog/doc-images/agent_editor_call_config.png)

The **Call Configuration** section of the [agent editor](/the-agent-editor) governs the mechanics of how your agent handles phone calls, from noise cancellation and ring behavior to call duration limits and idle handling. Start here when you need to reduce background noise, cap call length, adjust idle behavior, or enable voicemail handling.

## Noise cancellation

**Noise Cancellation** removes background noise (chatter in a café, keyboard typing) so the caller's voice is clearer and easier for the agent to understand. The recommended setting for most use cases is **Standard**. For environments with heavy background noise, switch to **Voice Isolation**, which leverages Krisp noise cancellation for more aggressive filtering.

## Ring duration

**Ring Duration** controls how long the phone rings before the agent picks up the call. A short ring (1 to 2 seconds) feels responsive for support lines, while a longer ring can feel more natural for outbound calls.

## Limit call duration

Toggle this on to cap how long a call can run. When enabled, the **Max. Call Duration** slider lets you set the limit up to 30 minutes. If the toggle is off, no fixed cap is enforced and the call ends only when the caller, the agent, or another rule stops it.

## Leave a voicemail

When enabled, the agent leaves a voicemail message after detecting that the call has reached voicemail, instead of simply hanging up.

Leaving a voicemail only works when the agent waits for the caller to speak first, since voicemail detection depends on listening for that opening audio. Switch the [greeting](/greeting-message-behavior) to **Human speaks first** before enabling **Leave a Voicemail**, and keep it on for as long as voicemail handling is on.

There are two modes:

| Mode              | Description                                                                                                                |
| ----------------- | -------------------------------------------------------------------------------------------------------------------------- |
| **Exact Message** | The agent speaks a fixed message that you provide. Use this when you need precise, consistent wording every time.          |
| **Prompt**        | The agent generates the voicemail message from a prompt. Use this when you want the message to vary or sound more natural. |

You can also configure this via the `voicemail_message` object on the [Create Assistant](/api-reference/platform-api/agents/create-assistant) and [Update Assistant](/api-reference/platform-api/agents/update-assistant) endpoints.

## Advanced settings

The settings below are collapsed under **Advanced Settings** by default. They give you control over idle behavior and ambient audio.

### Max. idle duration

**Max. Idle Duration** sets how long the agent waits for the caller to respond before automatically disconnecting. Avoid setting this too low. Callers sometimes need a moment to think or look something up, and a premature disconnect creates a poor experience.

### Idle reminders

When enabled, the agent sends a reminder message after the caller has been silent for a set period. You can customize the **Message** the agent says (for example, "I'm still here. Do you have any questions?") and the **Idle Duration** threshold that triggers it.

### Background noise

The **Background Noise** toggle adds subtle ambient audio to the call, making the conversation feel less sterile. This can help callers feel more comfortable, especially in consumer-facing use cases where a completely silent line may seem unnatural.

## FAQ

#### Why isn't my voicemail message playing?

Voicemail handling requires [Human Speaks First](/greeting-message-behavior) so the agent can listen for the initial speaker and recognize a voicemail greeting. If your agent uses an automatic greeting, switch the greeting mode and re-enable **Leave a Voicemail**.

#### What's the difference between Standard and Voice Isolation?

**Standard** is the default and works for most environments. **Voice Isolation** uses Krisp for more aggressive noise cancellation, which is better for callers in cafés, airports, or open offices but slightly more intrusive on the audio.

#### Can I cap a call beyond 30 minutes?

The **Max. Call Duration** slider tops out at 30 minutes. For longer calls, leave **Limit Call Duration** off and rely on the agent's own end-call logic or other guardrails to stop the conversation.