Cartesia

Cartesia implementation for @micdrop/server.

This package provides high-quality real-time text-to-speech implementation using Cartesia’s streaming API. Before you pick a voice engine, you can compare Cartesia and ElevenLabs for a voice agent on latency, voices, price and concurrency.

Installation

npm install @micdrop/cartesia

Cartesia TTS (Text-to-Speech)

Usage with MicdropServer

import { CartesiaTTS } from '@micdrop/cartesia'
import { MicdropServer } from '@micdrop/server'

const tts = new CartesiaTTS({
  apiKey: process.env.CARTESIA_API_KEY || '',
  modelId: 'sonic-3.6', // Cartesia model ID
  voiceId: 'a0e99841-438c-4a64-b679-ae501e7d6091', // Voice ID
  language: 'en', // Optional: specify language
  generationConfig: { speed: 1.1 }, // Optional: speed, volume and emotion
})

// Use with MicdropServer
new MicdropServer(socket, {
  tts,
  // ... other options
})

Usage without MicdropServer

import { CartesiaTTS } from '@micdrop/cartesia'
import { Readable } from 'stream'

const tts = new CartesiaTTS({
  apiKey: process.env.CARTESIA_API_KEY || '',
  modelId: 'sonic-3.6',
  voiceId: 'a0e99841-438c-4a64-b679-ae501e7d6091',
})

// Audio is raw PCM, 16 bits, 16 kHz, mono
tts.on('Audio', (chunk) => console.log('Audio:', chunk.length, 'bytes'))
tts.on('Failed', (texts) => console.error('Failed:', texts))

tts.speak(Readable.from(['Hello! ', 'What can I do for you?']))

Events

Event	Payload	Description
`Audio`	`Buffer`	A chunk of audio, PCM 16 bits, 16 kHz, mono, ready to be played.
`Failed`	`string[]`	Synthesis gave up after its retries, with the text that stayed unspoken.

See the TTS interface for the full contract.

Options

Option	Type	Default	Description
`apiKey`	`string`	Required	Your Cartesia API key
`modelId`	`string`	Required	Cartesia model ID to use, such as `sonic-3.6`
`voiceId`	`string`	Required	Voice ID for speech synthesis
`language`	`CartesiaLanguage`	Optional	Language code for speech
`generationConfig`	`CartesiaGenerationConfig`	Optional	Speed, volume and emotion of the voice, see below
`speed`	`'fast' \| 'normal' \| 'slow'`	Optional	Deprecated, Sonic 3 models read `generationConfig.speed`
`connectionTimeout`	`number`	`5000`	Timeout in milliseconds for WebSocket connection
`retryDelay`	`number`	`1000`	Delay in milliseconds between reconnection attempts
`maxRetry`	`number`	`3`	Maximum number of reconnection attempts before failing

Models

Use sonic-3.6, the current Sonic model, or pin its snapshot sonic-3.6-2026-08-27 in production. Cartesia stops serving sonic-turbo and sonic-2 after October 20, 2026, so an agent configured with one of them has to switch its modelId before that date. The Cartesia model list gives every snapshot and its sunset date.

Speed, volume and emotion

generationConfig applies to every sentence the agent speaks. Cartesia treats its values as guidance and keeps the pacing natural.

Field	Type	Range	Description
`speed`	`number`	0.6 to 1.5	Speech speed, `1` by default
`volume`	`number`	0.5 to 2.0	Volume, `1` by default
`emotion`	`CartesiaEmotion`		Emotion the voice leans toward, such as `calm` or `content`, English only

const tts = new CartesiaTTS({
  apiKey: process.env.CARTESIA_API_KEY || '',
  modelId: 'sonic-3.6',
  voiceId: 'a0e99841-438c-4a64-b679-ae501e7d6091',
  generationConfig: { speed: 0.9, volume: 1.2, emotion: 'calm' },
})

To change the tone sentence by sentence, the LLM can write Cartesia’s emotion and speed tags into its answer, such as <emotion value="calm"/>.

Supported Languages

Sonic 3.6 speaks 44 languages:

Code	Language	Code	Language	Code	Language
`en`	English	`fr`	French	`de`	German
`es`	Spanish	`pt`	Portuguese	`zh`	Chinese
`ja`	Japanese	`hi`	Hindi	`it`	Italian
`ko`	Korean	`nl`	Dutch	`pl`	Polish
`ru`	Russian	`sv`	Swedish	`tr`	Turkish
`tl`	Tagalog	`bg`	Bulgarian	`ro`	Romanian
`ar`	Arabic	`cs`	Czech	`el`	Greek
`fi`	Finnish	`hr`	Croatian	`ms`	Malay
`sk`	Slovak	`da`	Danish	`ta`	Tamil
`uk`	Ukrainian	`hu`	Hungarian	`no`	Norwegian
`vi`	Vietnamese	`bn`	Bengali	`th`	Thai
`he`	Hebrew	`ka`	Georgian	`id`	Indonesian
`te`	Telugu	`gu`	Gujarati	`kn`	Kannada
`ml`	Malayalam	`mr`	Marathi	`pa`	Punjabi
`or`	Odia	`ur`	Urdu

Getting Started

Sign up for a Cartesia account and get your API key
Choose a model ID and voice ID from the Cartesia dashboard
Install the package and configure with your credentials

import { CartesiaTTS } from '@micdrop/cartesia'

const tts = new CartesiaTTS({
  apiKey: 'your-cartesia-api-key',
  modelId: 'sonic-3.6',
  voiceId: 'your-preferred-voice-id',
  language: 'en',
})

// Use with MicdropServer
new MicdropServer(socket, {
  tts,
  // ... other options
})