Use the API directly

Call the Text to Speech and Speech to Text APIs from your application. You do not need to build an agent first. The first HTTP example creates an audio file. The second returns a transcript. For streaming, see Stream in real time.

Before you begin

Set SLNG_API_KEY in your environment. If you need a key, follow Create your API key. If you already have one, see Store and use your key. The model requests below go to https://eu-west.slng.ai.ai and send your key as a bearer token.

Synthesize speech

Text to speech takes some text and a voice and returns audio. Pick the model in the request path and pass the text in the body. This example uses the Deepgram Aura model, where you choose the voice with the model parameter in the body. The endpoint returns binary audio, so write the response straight to a file.

curl
JavaScript
SDK
Python
CLI

curl https://eu-west.slng.ai.ai/v1/tts/slng/deepgram/aura:2-en \
  -H "Authorization: Bearer $SLNG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "aura-2-thalia-en",
    "text": "Hello from sunny Barcelona!"
  }' \
  --output hello.wav

const response = await fetch(
  "https://eu-west.slng.ai.ai/v1/tts/slng/deepgram/aura:2-en",
  {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.SLNG_API_KEY}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      model: "aura-2-thalia-en",
      text: "Hello from sunny Barcelona!",
    }),
  },
);

const audioData = await response.arrayBuffer();
// Play or save audioData

The voiceai-sdk client reads SLNG_API_KEY from the environment and handles the endpoint for you.

npm install voiceai-sdk

import { writeFile } from "node:fs/promises";
import Slng from "voiceai-sdk";

const client = new Slng();

const response = await client.textToSpeech.create("slng/deepgram/aura:2-en", {
  text: "Hello from sunny Barcelona!",
  voice: "aura-2-thalia-en",
});

await writeFile("hello.wav", Buffer.from(await response.arrayBuffer()));

import os
import requests

url = "https://eu-west.slng.ai.ai/v1/tts/slng/deepgram/aura:2-en"
headers = {
    "Authorization": f"Bearer {os.environ['SLNG_API_KEY']}",
    "Content-Type": "application/json",
}
data = {
    "model": "aura-2-thalia-en",
    "text": "Hello from sunny Barcelona!",
}

response = requests.post(url, headers=headers, json=data)
with open("hello.wav", "wb") as f:
    f.write(response.content)

The voiceai CLI wraps the same API. Run voiceai login once to store your key.

npm install -g voiceai-cli
voiceai login
voiceai tts "Hello from sunny Barcelona!" --out hello.wav

The call above produces this audio:

Transcribe audio

Speech to text takes an audio file and returns the transcript. Send the file as multipart form data and read the text from the first alternative. The examples below transcribe this sample:

curl
JavaScript
SDK
Python
CLI

curl https://eu-west.slng.ai.ai/v1/stt/slng/deepgram/nova:3-en \
  -H "Authorization: Bearer $SLNG_API_KEY" \
  -F "audio=@micro-machines.wav"

const formData = new FormData();
formData.append("audio", audioFile); // File from <input type="file">

const response = await fetch(
  "https://eu-west.slng.ai.ai/v1/stt/slng/deepgram/nova:3-en",
  {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.SLNG_API_KEY}`,
    },
    body: formData,
  },
);

const result = await response.json();
console.log(result.results.channels[0].alternatives[0].transcript);

The voiceai-sdk client takes a file stream and returns the transcript directly.

import fs from "node:fs";
import Slng from "voiceai-sdk";

const client = new Slng();

const transcript = await client.speechToText.create("slng/deepgram/nova:3-en", {
  audio: fs.createReadStream("micro-machines.wav"),
});

console.log(transcript.alternatives[0]?.transcript);

import os
import requests

url = "https://eu-west.slng.ai.ai/v1/stt/slng/deepgram/nova:3-en"
headers = {"Authorization": f"Bearer {os.environ['SLNG_API_KEY']}"}

with open("micro-machines.wav", "rb") as audio_file:
    response = requests.post(url, headers=headers, files={"audio": audio_file})

result = response.json()
print(result["results"]["channels"][0]["alternatives"][0]["transcript"])

voiceai stt micro-machines.wav

The transcript comes back under results.channels[0].alternatives[0].transcript.

Change the model or parameters

The model is part of the request path. Swap it to change the voice engine or the language, and keep the rest of the call the same. Prefer a variant under the slng/ prefix where one exists: those run on SLNG infrastructure in the region closest to you, so each call skips the hop to an outside provider. Each model has its own endpoint and its own parameters, so the field that picks the voice differs by provider. Deepgram Aura uses model, Rime Arcana uses speaker.

# Rime Arcana instead of Deepgram Aura
curl https://eu-west.slng.ai.ai/v1/tts/slng/fish/tts:s2.1-pro \
  -H "Authorization: Bearer $SLNG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "text": "Hello from sunny Barcelona!",
    "reference_id": "16cabdb7f8d240569aff36c9e480d783"
  }' \
  --output hello-arcana.wav

For speech to text, add optional fields to the form to tune the transcript:

language sets the recognition language.
diarize=true labels each speaker.
punctuate=true adds punctuation.

See WebSockets vs HTTP for request and response formats, and the Unified API guide for more details.

Stream in real time

For low-latency, turn-by-turn audio, connect over WebSocket at wss://eu-west.slng.ai.ai instead of posting a whole file.

Find other models and API details

Which models are available and the model catalog, including views by region and language.
Text to speech API and speech to text API.
Authentication, rate limits, and error codes.

Next steps

Ready to build a full voice agent instead? See create an agent.
Already run an agent elsewhere? See improve an existing agent.

Get started

Regions

Execution layer

Agent Builder

Models

Integrate

Before you begin

Synthesize speech

Transcribe audio

Change the model or parameters

Stream in real time

Find other models and API details

Next steps

​Before you begin

​Synthesize speech

​Transcribe audio

​Change the model or parameters

​Stream in real time

​Find other models and API details

​Next steps

Before you begin

Synthesize speech

Transcribe audio

Change the model or parameters

Stream in real time

Find other models and API details

Next steps