EdgeSpeech

Web developers can add listening, speaking, or both to a React Native app with EdgeSpeech, without writing any native audio code. Voice Activity Detection, Speech-to-Text, and Text-to-Speech all run on-device through the Switchboard SDK. Your JavaScript works entirely with text.

import { SwitchboardVoiceModule, initialize, listen, speak } from '@synervoz/edgespeech'

initialize('YOUR_APP_ID', 'YOUR_APP_SECRET')

SwitchboardVoiceModule.addListener('onTranscript', async ({ text, isFinal }) => {
  if (isFinal) {
    const response = await chat(text)
    await speak(response)
  }
})

await listen()

The example app shows the complete voice loop running end-to-end.

Cost Savings: 99% Cheaper Than Cloud Speech-to-Speech

The real advantage of on-device voice processing is cost.

The Math

Consider a voice AI assistant handling 1,000 conversations per day, each lasting 5 minutes.

OpenAI Realtime API (cloud speech-to-speech): | Component | Calculation | Cost | |-----------|-------------|------| | Audio input | 150 sec × 80 tokens/sec × $100/1M | $1.20 | | Audio output | 150 sec × 80 tokens/sec × $200/1M | $2.40 | | Per conversation | | $3.60 | | 1,000 conversations/day | | $3,600/day | | Monthly (30 days) | | $108,000 |

EdgeSpeech + ChatGPT API (text only): | Component | Calculation | Cost | |-----------|-------------|------| | Text input | ~750 tokens × $5/1M | $0.004 | | Text output | ~750 tokens × $20/1M | $0.015 | | Per conversation | | $0.02 | | 1,000 conversations/day | | $20/day | | Monthly (30 days) | | $600 |

Installation

npm install @synervoz/edgespeech

iOS Setup — Expo (managed or bare)

1. The Switchboard SDK frameworks are downloaded automatically when you run npm install. No separate setup command is needed.

2. Add microphone permission to your Info.plist (or via app.json infoPlist for Expo managed workflow):

<key>NSMicrophoneUsageDescription</key>
<string>This app needs microphone access for voice input</string>

3. Build your app:

npx expo run:ios

iOS Setup — Bare React Native (without Expo)

EdgeSpeech uses expo-modules-core as its native module bridge. You need this package even in a project that otherwise does not use Expo.

1. Install expo-modules-core:

npm install expo-modules-core

2. Run npm install @synervoz/edgespeech. The Switchboard SDK frameworks download automatically — no separate setup script is needed.

3. Add the Expo autolinking require to the top of ios/Podfile, before any target blocks:

require File.join(
  File.dirname(`node --print "require.resolve('expo-modules-core/package.json')"`),
  "scripts/autolinking"
)

4. Inside your main app target, call use_expo_modules!:

target 'YourApp' do
  use_expo_modules!
  # ... your other pods
end

use_expo_modules! discovers all installed packages that include an expo-module.config.json (including EdgeSpeech) and links them automatically.

5. Install pods:

cd ios && pod install

6. Add microphone permission to ios/YourApp/Info.plist:

<key>NSMicrophoneUsageDescription</key>
<string>This app needs microphone access for voice input</string>

7. Build your app:

npx react-native run-ios
# or open ios/YourApp.xcworkspace in Xcode

Quick Start

import {
  SwitchboardVoiceModule,
  initialize,
  configure,
  listen,
  speak,
  requestMicrophonePermission,
} from '@synervoz/edgespeech'

// 1. Initialize with your Switchboard credentials
initialize('YOUR_SWITCHBOARD_APP_ID', 'YOUR_SWITCHBOARD_APP_SECRET')

// 2. (Optional) tune settings
configure({ vadSensitivity: 0.5 })

// 3. Set up event listeners
SwitchboardVoiceModule.addListener('onTranscript', ({ text, isFinal }) => {
  console.log(isFinal ? 'Final:' : 'Interim:', text)
  if (isFinal) handleUserSpeech(text)
})

SwitchboardVoiceModule.addListener('onStateChange', ({ state }) => {
  console.log('State:', state) // 'idle' | 'listening' | 'speaking'
})

SwitchboardVoiceModule.addListener('onInterrupted', () => {
  console.log('User interrupted playback')
})

SwitchboardVoiceModule.addListener('onError', ({ code, message }) => {
  console.error('Voice error:', code, message)
})

// 4. Request permission and start
const granted = await requestMicrophonePermission()
if (granted) {
  await listen()
}

// 5. Speak responses
await speak('Hello! How can I help you today?')

API Reference

Configuration

await EdgeSpeech.configure({
  appId: string,           // Required: Switchboard app ID
  appSecret: string,       // Required: Switchboard app secret
  sttModel?: string,       // Optional: STT model (default: 'whisper-base-en')
  ttsVoice?: string,       // Optional: TTS voice (default: 'en_GB')
  vadSensitivity?: number, // Optional: VAD sensitivity 0.0-1.0 (default: 0.5)
});

Methods

| Method | Description | | ------------------------------- | ---------------------------------------- | | configure(config) | Initialize with credentials and settings | | listen() | Start listening for voice input | | stopListening() | Stop listening | | speak(text) | Speak text using TTS | | stopSpeaking() | Stop current TTS playback | | requestMicrophonePermission() | Request microphone access |

Events

Listen via SwitchboardVoiceModule.addListener(eventName, handler).

| Event | Payload | Description | | --------------- | ------------------------------------ | ----------------------------------------------- | | onTranscript | { text: string, isFinal: boolean } | Speech recognized | | onStateChange | { state: string } | State changed (idle, listening, speaking) | | onSpeechStart | {} | VAD detected voice activity | | onSpeechEnd | {} | VAD detected end of speech | | onTTSComplete | {} | TTS finished playing | | onInterrupted | {} | TTS interrupted by user speech | | onError | { code: string, message: string } | Error occurred |

States

idle -> listening -> processing -> idle
                 \              /
                   -> speaking -

Example App

The example/ directory contains a minimal demo showing the complete voice loop:

cd example
npm install
npx expo run:ios

Architecture

flowchart TB
    mic["🎤 Microphone"]
    spk["🔊 Speaker"]

    subgraph Engines["EdgeSpeech"]
        subgraph JS["JavaScript API"]
            subgraph Controls["Controls"]
                listen["listen()"]
                stopListening["stopListening()"]
                stopSpeaking["stopSpeaking()"]
            end
            speak["speak(text)"]
            onTranscript["onTranscript"]
            onInterrupted["onInterrupted"]
        end
        subgraph ListenGraph["Listening Graph"]
            direction LR
            MCtoMono["MultiChannelToMono"] --> Split["BusSplitter"]
            Split --> VAD["SileroVAD"]
            Split --> STT["Whisper STT"]
            VAD -.-> STT
        end

        subgraph SpeakingGraph["Speaking Graph"]
            TTS["Sherpa TTS"]
        end
    end

    SDK["Switchboard SDK (Runtime)"]

    mic --> ListenGraph
    SpeakingGraph --> spk
    ListenGraph -- "executed by" --> SDK
    SpeakingGraph -- "executed by" --> SDK

    listen --> ListenGraph
    stopListening --> ListenGraph
    speak --> SpeakingGraph
    stopSpeaking --> SpeakingGraph

    STT -.-> onTranscript
    ListenGraph -.-> onInterrupted
    onInterrupted --> stopSpeaking

    onTranscript --> LLM
    LLM --> speak

    LLM["🤖 Your LLM Pipeline"]:::external

    classDef external fill:#f5f5f5,stroke:#999,stroke-dasharray: 5 5

    style ListenGraph fill:#fff,stroke:#999,stroke-dasharray: 5 5
    style SpeakingGraph fill:#fff,stroke:#999,stroke-dasharray: 5 5

Platform Support

| Platform | Status | | -------- | ----------- | | iOS | Supported | | Android | Coming soon |

Requirements

| Requirement | Minimum | Notes | |-------------|---------|-------| | React Native | 0.74+ | Declared in peerDependencies; not enforced at install time | | iOS | 13.4+ | Enforced by the podspec (s.platforms = { :ios => "13.4" }) | | Node.js | 20+ | Required for all tooling; engines field in package.json specifies >=22 | | expo-modules-core | 2.0.0+ | Required peer dependency; included automatically with Expo, must be installed explicitly for bare React Native |

Get Switchboard Credentials

1. Sign up at switchboard.audio
2. Create a new app in the dashboard
3. Copy your App ID and App Secret

Releasing

Releases are published to npm automatically when a version tag is pushed. Versions follow Semantic Versioning: MAJOR.MINOR.PATCH — increment MAJOR for breaking changes, MINOR for new features, PATCH for bug fixes.

1. Bump the version in package.json.
2. Commit: git commit -am "chore: release vX.Y.Z"
3. Tag and push:

git tag vX.Y.Z
git push origin main --tags

The release workflow builds the package and publishes to npm under the @synervoz scope using npm publish --access public. Requires an NPM_TOKEN secret configured in the repository settings.

Tests

Run unit tests with:

npm test

License

MIT

Links

• Switchboard SDK Documentation
• Example App
• GitHub Issues