> For a complete documentation index, fetch https://docs.voximplant.ai/llms.txt
# Example: Speech-to-speech translation
> This example answers an inbound English call, dials a Spanish-speaking callee, and uses Gemini Live API to translate the caller’s speech into Spanish audio in real time.
For the complete documentation index, see llms.txt.
This example answers an inbound English call, dials a Spanish-speaking callee, and uses Gemini Live API to translate the caller’s speech into Spanish audio in real time.
**⬇️ Jump to the [Full VoxEngine scenario](#full-voxengine-scenario).**
This page reflects the current `gemini-3.1-flash-live-preview` flow from Google’s Live API docs:
[https://ai.google.dev/gemini-api/docs/models/gemini-3.1-flash-live-preview](https://ai.google.dev/gemini-api/docs/models/gemini-3.1-flash-live-preview)
## Prerequisites
* Set up an inbound entrypoint for the caller:
* Phone number: [https://voximplant.com/docs/getting-started/basic-concepts/phone-numbers](https://voximplant.com/docs/getting-started/basic-concepts/phone-numbers)
* WhatsApp: [https://voximplant.com/docs/guides/integrations/whatsapp](https://voximplant.com/docs/guides/integrations/whatsapp)
* SIP user / SIP registration: [https://voximplant.com/docs/guides/calls/sip](https://voximplant.com/docs/guides/calls/sip)
* App user: [https://voximplant.com/docs/getting-started/basic-concepts/users](https://voximplant.com/docs/getting-started/basic-concepts/users) (see also [https://voximplant.com/docs/guides/calls/scenarios#how-to-call-a-voximplant-user](https://voximplant.com/docs/guides/calls/scenarios#how-to-call-a-voximplant-user))
* Create a routing rule that points the destination (phone number / WhatsApp / SIP username / app user alias) to this scenario: [https://voximplant.com/docs/getting-started/basic-concepts/routing-rules](https://voximplant.com/docs/getting-started/basic-concepts/routing-rules)
* Store your Gemini API key in Voximplant [Secrets](/platform/voxengine/secrets) under `GEMINI_API_KEY`.
* Store the following non-sensitive values in Voximplant `ApplicationStorage`:
* `CALLEE_DESTINATION` (Spanish-speaking callee, e.g. `+34911222333`)
* `PSTN_CALLER_ID` (verified caller ID / purchased Voximplant number)
## Demo video
Video link: [Gemini Live speech-to-speech translation demo](https://www.youtube.com/watch?v=B9zjcMIF7eM)
## Session setup
The Gemini Live API session is configured via `connectConfig`, passed into `Gemini.createLiveAPIClient(...)`.
In the full scenario, see `GEMINI_CONNECT_CONFIG`:
* `responseModalities: ["AUDIO"]` asks Gemini to speak back in real time.
* `thinkingConfig: { thinkingLevel: "minimal" }` reduces latency.
* `realtimeInputConfig.automaticActivityDetection` tunes barge-in behavior.
* `speechConfig` selects a prebuilt voice for the translated audio.
* `systemInstruction` enforces the English → Spanish translation behavior.
* `inputAudioTranscription` and `outputAudioTranscription` are enabled so you can log translated text during the session.
## Translation pipeline (one-way)
This example uses a one-way pipeline:
```
English caller -> Gemini Live API -> Spanish callee
```
The code wires the audio like this:
```js title="Connect audio"
call.sendMediaTo(geminiLiveAPIClient);
geminiLiveAPIClient.sendMediaTo(calleeCall);
```
## Barge-in
Gemini includes an `interrupted` flag in `ServerContent` when the caller speaks over TTS. The example clears the media buffer so Gemini stops speaking immediately:
```js title="Barge-in handling"
if (payload.interrupted !== undefined) {
geminiLiveAPIClient.clearMediaBuffer();
}
```
## Events
The scenario listens for `Gemini.LiveAPIEvents.ServerContent`. If transcripts are enabled, the example logs both languages:
```js title="Transcripts"
if (payload.inputTranscription?.text) Logger.write(`===EN=== ${payload.inputTranscription.text}`);
if (payload.outputTranscription?.text) Logger.write(`===ES=== ${payload.outputTranscription.text}`);
```
For illustration, it also logs these events:
* `Gemini.LiveAPIEvents`: `SetupComplete`, `ServerContent`, `ConnectorInformation`, `Unknown`
* `Gemini.Events`: `WebSocketMediaStarted`, `WebSocketMediaEnded`
## Notes
* This example uses the Gemini Developer API (`Gemini.Backend.GEMINI_API`).
* The current sample uses `gemini-3.1-flash-live-preview`.
* Translation is one-way (English → Spanish). For bidirectional translation, run two Gemini sessions with opposite instructions.
* The example includes short prompts (`call.say` / `calleeCall.say`) to make recordings easier to follow. Remove them for production.
If you are updating an older `2.5` translation sample, replace `thinkingBudget` with `thinkingLevel`. For `3.1`, this example also sends a short `sendRealtimeInput(...)` startup instruction on `SetupComplete` so the live interpretation session begins reliably.
[See the VoxEngine API Reference for more details](https://voximplant.com/docs/references/voxengine/gemini).
## Full VoxEngine scenario
```javascript title={"voxeengine-gemini-s2s-translate.js"} maxLines={0}
/**
* Voximplant + Gemini Live API connector demo
* Scenario: real-time speech-to-speech translation (English -> Spanish).
*/
require(Modules.Gemini);
require(Modules.ApplicationStorage);
const SYSTEM_INSTRUCTIONS = `
You are a REAL-TIME INTERPRETER.
Task:
- Translate everything you hear from English to Spanish.
Rules:
- Output ONLY the Spanish translation (no English, no explanations, no extra commentary).
- Preserve meaning, tone, names, numbers, and proper nouns.
- Keep latency low: translate phrase-by-phrase as soon as you have enough context.
- Do NOT greet or introduce yourself. Speak ONLY when the caller speaks.
`;
const GEMINI_MODEL = "gemini-3.1-flash-live-preview";
VoxEngine.addEventListener(AppEvents.CallAlerting, async ({call}) => {
let voiceAIClient;
let calleeCall;
let terminated = false;
const terminate = () => {
if (terminated) return;
terminated = true;
calleeCall?.hangup();
call?.hangup();
VoxEngine.terminate();
};
call.answer();
call.record({hd_audio: true, stereo: true});
call.addEventListener(CallEvents.Disconnected, terminate);
call.addEventListener(CallEvents.Failed, terminate);
const geminiApiKey = VoxEngine.getSecretValue('GEMINI_API_KEY');
const calleeDestination = (await ApplicationStorage.get("CALLEE_DESTINATION")).value;
calleeCall = VoxEngine.callPSTN(calleeDestination, (await ApplicationStorage.get("PSTN_CALLER_ID")).value);
// Or call via an app user, SIP, or WhatsApp by uncommenting one of the lines below and commenting out the line above.
// calleeCall = VoxEngine.callUser(calleeDestination);
// calleeCall = VoxEngine.callSIP(`sip:${calleeDestination}@your-sip-domain`, (await ApplicationStorage.get("PSTN_CALLER_ID")).value);
// calleeCall = VoxEngine.callWhatsappUser({number: calleeDestination, callerid: (await ApplicationStorage.get("PSTN_CALLER_ID")).value)});
calleeCall.addEventListener(CallEvents.Disconnected, terminate);
calleeCall.addEventListener(CallEvents.Failed, terminate);
calleeCall.addEventListener(CallEvents.Connected, async () => {
calleeCall.record({hd_audio: true, stereo: true});
// Optional prompts to make the demo obvious on recordings.
call.say("Connected. Speak in English. The other party will hear Spanish.");
calleeCall.say("Connected. You will hear Spanish translation in real time.");
const GEMINI_CONNECT_CONFIG = {
responseModalities: ["AUDIO"],
thinkingConfig: {thinkingLevel: "minimal"},
realtimeInputConfig: {
automaticActivityDetection: {
disabled: false,
prefixPaddingMs: 20,
silenceDurationMs: 200,
},
},
speechConfig: {
voiceConfig: {
prebuiltVoiceConfig: {voiceName: "Achird"},
},
},
inputAudioTranscription: {},
outputAudioTranscription: {},
systemInstruction: {
parts: [{text: SYSTEM_INSTRUCTIONS}],
},
};
try {
voiceAIClient = await Gemini.createLiveAPIClient({
apiKey: geminiApiKey,
model: GEMINI_MODEL,
backend: Gemini.Backend.GEMINI_API,
connectConfig: GEMINI_CONNECT_CONFIG,
onWebSocketClose: (event) => {
Logger.write("===Gemini.WebSocket.Close===");
if (event) Logger.write(JSON.stringify(event));
terminate();
},
});
// Caller (English) -> Gemini -> Callee (Spanish)
call.sendMediaTo(voiceAIClient);
voiceAIClient.sendMediaTo(calleeCall);
voiceAIClient.addEventListener(Gemini.LiveAPIEvents.SetupComplete, (event) => {
Logger.write("===Gemini.LiveAPIEvents.SetupComplete===");
if (event?.data) Logger.write(JSON.stringify(event.data));
voiceAIClient.sendRealtimeInput({
text: "Start real-time English to Spanish interpretation now. Do not greet. Only translate the caller's speech for the other party.",
});
});
voiceAIClient.addEventListener(Gemini.LiveAPIEvents.ServerContent, (event) => {
const payload = event?.data?.payload || {};
if (payload.inputTranscription?.text) {
Logger.write(`===EN=== ${payload.inputTranscription.text}`);
}
if (payload.outputTranscription?.text) {
Logger.write(`===ES=== ${payload.outputTranscription.text}`);
}
if (payload.interrupted !== undefined) {
Logger.write("===BARGE-IN=== Gemini.LiveAPIEvents.ServerContent");
voiceAIClient.clearMediaBuffer();
}
});
[
Gemini.LiveAPIEvents.SetupComplete,
Gemini.LiveAPIEvents.ServerContent,
Gemini.LiveAPIEvents.ConnectorInformation,
Gemini.LiveAPIEvents.Unknown,
Gemini.Events.WebSocketMediaStarted,
Gemini.Events.WebSocketMediaEnded,
].forEach((eventName) => {
voiceAIClient.addEventListener(eventName, (event) => {
Logger.write(`===${event.name}===`);
if (event?.data) Logger.write(JSON.stringify(event.data));
});
});
} catch (error) {
Logger.write("===SOMETHING_WENT_WRONG===");
Logger.write(error);
terminate();
}
});
});
```