> ## Documentation Index > Fetch the complete documentation index at: https://docs.nineninesix.ai/llms.txt > Use this file to discover all available pages before exploring further. # Create Speech > Generate audio from text using the Nineninesix TTS API. ## POST /tts/bytes Generates audio from the input transcript. The response body is the raw audio in the requested format, streamed as it's generated. ### Request Body | Parameter | Type | Required | Description | | --------------- | ------ | -------- | -------------------------------------------------------- | | `model_id` | string | Yes | The TTS model. Currently `gepard-1.0`. | | `transcript` | string | Yes | The text to synthesize. | | `voice` | object | Yes | Voice specifier: `{ "mode": "id", "id": "" }`. | | `output_format` | object | Yes | Output format (see below). | | `language` | string | No | Language code (e.g. `en`). | ### Output Format `output_format` has three fields, each validated against a fixed set. Anything outside these values returns `400` — the API does not silently fall back. | Field | Allowed values | | ------------- | ------------------------------------ | | `container` | `raw`, `wav` | | `encoding` | `pcm_s16le`, `pcm_mulaw`, `pcm_alaw` | | `sample_rate` | `8000`, `16000`, `22050` | * The model is natively **22050 Hz** — use it to skip resampling; `8000`/`16000` are resampled server-side. * **Container by endpoint:** `wav` is available **only on `/tts/bytes`**. Streaming endpoints (`/tts/sse`, `/tts/websocket`) are **`raw`-only** — there's no place to put a RIFF/WAV header in a chunked stream. * **`pcm_mulaw` / `pcm_alaw`** are 8-bit G.711 telephony codecs. Browsers can't play them directly; decode to linear PCM first (or hand them straight to your telephony stack). ```json theme={null} // WAV (PCM) — /tts/bytes only { "container": "wav", "encoding": "pcm_s16le", "sample_rate": 22050 } // Raw PCM — lowest latency for streaming pipelines { "container": "raw", "encoding": "pcm_s16le", "sample_rate": 22050 } ``` #### Telephony (G.711) For Twilio / SIP media streams, request 8 kHz μ-law or A-law raw: ```json theme={null} // μ-law @ 8 kHz (US/telephony) { "container": "raw", "encoding": "pcm_mulaw", "sample_rate": 8000 } // A-law @ 8 kHz (EU/telephony) { "container": "raw", "encoding": "pcm_alaw", "sample_rate": 8000 } ``` **Removed formats.** `mp3` (container) and `pcm_f32le` (encoding), plus sample rates `24000` / `44100` / `48000`, are **not supported** and now return `400`. Request `wav` + `pcm_s16le` and transcode client-side if you need another format. ### Models | Model | Description | | ------------ | --------------------------------------------------------------------------------- | | `gepard-1.0` | Dialogue-native model, tuned for conversational speech and low-latency streaming. | ### Billing 1 credit = 1 character of `transcript` (Unicode code points). The charge is taken before generation and refunded automatically on failure. ### Examples ```bash curl theme={null} curl -N https://api.nineninesix.ai/tts/bytes \ -H "Authorization: Bearer sk_996_your_api_key" \ -H "Content-Type: application/json" \ -d '{ "model_id": "gepard-1.0", "transcript": "Today is a wonderful day to build something people love!", "voice": { "mode": "id", "id": "" }, "output_format": { "container": "wav", "encoding": "pcm_s16le", "sample_rate": 22050 } }' --output speech.wav ``` ```python Python theme={null} from cartesia import Cartesia client = Cartesia(api_key="sk_996_your_api_key", base_url="https://api.nineninesix.ai") audio = client.tts.bytes( model_id="gepard-1.0", transcript="Today is a wonderful day to build something people love!", voice={"mode": "id", "id": ""}, output_format={"container": "wav", "encoding": "pcm_s16le", "sample_rate": 22050}, ) with open("speech.wav", "wb") as f: f.write(audio) ``` ```typescript Node.js theme={null} import { Cartesia } from "@cartesia/cartesia-js"; const client = new Cartesia({ apiKey: "sk_996_your_api_key", baseURL: "https://api.nineninesix.ai" }); const res = await client.tts.generate({ model_id: "gepard-1.0", transcript: "Today is a wonderful day to build something people love!", voice: { mode: "id", id: "" }, output_format: { container: "wav", encoding: "pcm_s16le", sample_rate: 22050 }, }); const buffer = Buffer.from(await res.arrayBuffer()); fs.writeFileSync("speech.wav", buffer); ``` ## POST /tts/sse Streams audio over Server-Sent Events for low time-to-first-audio without opening a WebSocket. The request body is identical to `/tts/bytes`, except the container must be `raw` (SSE can't wrap a WAV/RIFF header): ```json theme={null} { "container": "raw", "encoding": "pcm_s16le", "sample_rate": 22050 } ``` Each event's `data` is a JSON object. `chunk` events carry a base64-encoded slice of raw PCM; a final `done` event closes the stream: ``` data: {"type":"chunk","data":"","context_id":"..."} data: {"type":"chunk","data":"","context_id":"..."} data: {"type":"done","context_id":"..."} ``` Billing is identical to `/tts/bytes` — one pre-charge on the full transcript, confirmed when the stream completes. ```typescript Node.js theme={null} import { Cartesia } from "@cartesia/cartesia-js"; const client = new Cartesia({ apiKey: "sk_996_your_api_key", baseURL: "https://api.nineninesix.ai" }); const stream = await client.tts.generateSSE({ model_id: "gepard-1.0", transcript: "Streaming speech, chunk by chunk.", voice: { mode: "id", id: "" }, output_format: { container: "raw", encoding: "pcm_s16le", sample_rate: 22050 }, }); for await (const message of stream) { if (message.type === "chunk") { const pcm = Buffer.from(message.data, "base64"); // feed into your audio sink } } ``` ```python Python theme={null} import base64 from cartesia import Cartesia client = Cartesia(api_key="sk_996_your_api_key", base_url="https://api.nineninesix.ai") for message in client.tts.sse( model_id="gepard-1.0", transcript="Streaming speech, chunk by chunk.", voice={"mode": "id", "id": ""}, output_format={"container": "raw", "encoding": "pcm_s16le", "sample_rate": 22050}, ): if message.type == "chunk": pcm = base64.b64decode(message.data) # feed into your audio sink ``` ## WebSocket Streaming For real-time, low-latency generation over a persistent connection — `wss://api.nineninesix.ai/tts/websocket` — see the [WebSocket Streaming](/api-reference/tts/websocket) page, which includes the send/receive message schemas and an interactive **Connect** playground.