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Early Beta — The Web SDK is in early beta. APIs may change between releases.

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Overview

The Web SDK supports multiple TTS voice models via Piper TTS (VITS architecture) compiled to WebAssembly through sherpa-onnx. This page covers available voices, switching voices, and managing multiple voice models.

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Available Voices

The Web SDK uses Piper TTS voice models in ONNX format. These are neural voices that produce natural-sounding speech.
VoiceLanguageQualitySizeSpeed
en_US-lessac-mediumEnglish (US)High~65MBFast
en_US-amy-mediumEnglish (US)High~65MBFast
en_GB-alba-mediumEnglish (UK)High~65MBFast
de_DE-thorsten-mediumGermanHigh~65MBFast
fr_FR-siwis-mediumFrenchHigh~65MBFast
es_ES-davefx-mediumSpanishHigh~65MBFast
Piper TTS has hundreds of voices in many languages. Browse the full catalog at Piper Samples.

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Loading a Voice

import { TTS } from '@runanywhere/web'

await TTS.loadVoice({
  voiceId: 'piper-en-lessac',
  modelPath: '/models/en_US-lessac-medium.onnx',
  tokensPath: '/models/tokens.txt',
  dataDir: '/models/espeak-ng-data',
})

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Switching Voices

Unload the current voice before loading a new one: 
// Unload current voice
await TTS.unloadVoice()

// Load a different voice
await TTS.loadVoice({
  voiceId: 'piper-de-thorsten',
  modelPath: '/models/de_DE-thorsten-medium.onnx',
  tokensPath: '/models/tokens.txt',
  dataDir: '/models/espeak-ng-data',
})

// Synthesize in German
const result = await TTS.synthesize('Hallo, willkommen bei RunAnywhere!')

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Voice Properties

Check the currently loaded voice: 
console.log('Voice loaded:', TTS.isVoiceLoaded)
console.log('Voice ID:', TTS.voiceId)
console.log('Sample rate:', TTS.sampleRate) // typically 22050
console.log('Number of speakers:', TTS.numSpeakers)

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Multi-Speaker Models

Some Piper voice models include multiple speakers. Select a speaker by ID: 
// Check available speakers
console.log('Speakers:', TTS.numSpeakers)

// Synthesize with different speakers
const speaker0 = await TTS.synthesize('Hello!', { speakerId: 0 })
const speaker1 = await TTS.synthesize('Hello!', { speakerId: 1 })

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Voice Configuration Options

interface TTSVoiceConfig {
  /** Unique voice identifier */
  voiceId: string

  /** Path to VITS/Piper ONNX model file */
  modelPath: string

  /** Path to tokens.txt file */
  tokensPath: string

  /** Path to espeak-ng-data directory */
  dataDir?: string

  /** Path to custom lexicon file */
  lexicon?: string

  /** Number of inference threads (default: 1) */
  numThreads?: number
}

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Clean Up

Release TTS resources when no longer needed: 
await TTS.unloadVoice()
TTS.cleanup()

Synthesize

Text-to-Speech synthesis

TTS Output

Working with audio output

Voice Agent

Full voice pipeline