Web Audio API

Web Audio API Skill

1. Overview

This skill provides Web Audio API expertise for creating audio feedback, voice processing, and sound effects in the JARVIS AI Assistant.

Risk Level: LOW - Audio processing with minimal security surface

Primary Use Cases:

• HUD audio feedback (beeps, alerts)
• Voice input processing
• Spatial audio for 3D HUD elements
• Real-time audio visualization
• Text-to-speech integration

2. Core Responsibilities

2.1 Fundamental Principles

1. TDD First: Write tests before implementation for all audio components
2. Performance Aware: Optimize for 60fps with minimal audio latency
3. User Gesture Required: Audio context must be started after user interaction
4. Resource Cleanup: Close audio contexts and disconnect nodes on unmount
5. AudioWorklet for Processing: Use AudioWorklet for heavy DSP operations
6. Accessibility: Provide visual alternatives to audio feedback
7. Volume Control: Respect system and user volume preferences
8. Error Handling: Gracefully handle audio permission denials

3. Technology Stack & Versions

3.1 Browser Support

3.2 TypeScript Types

// types/audio.ts
interface AudioFeedbackOptions {
  frequency: number
  duration: number
  type: OscillatorType
  volume: number
}

interface SpatialAudioPosition {
  x: number
  y: number
  z: number
}

4. Implementation Patterns

4.1 Audio Context Management

// composables/useAudioContext.ts
export function useAudioContext() {
  const audioContext = ref<AudioContext | null>(null)
  const isInitialized = ref(false)

  async function initialize() {
    if (audioContext.value) return
    audioContext.value = new AudioContext()
    if (audioContext.value.state === 'suspended') await audioContext.value.resume()
    isInitialized.value = true
  }

  onUnmounted(() => {
    audioContext.value?.close()
    audioContext.value = null
  })

  return { audioContext: readonly(audioContext), isInitialized: readonly(isInitialized), initialize }
}

4.2 HUD Beep Feedback

// composables/useHUDSounds.ts
export function useHUDSounds() {
  const { audioContext, initialize } = useAudioContext()

  async function playBeep(options: Partial<AudioFeedbackOptions> = {}) {
    await initialize()
    const ctx = audioContext.value
    if (!ctx) return

    const { frequency = 440, duration = 0.1, type = 'sine', volume = 0.3 } = options
    const safeVolume = Math.max(0, Math.min(1, volume))

    const oscillator = ctx.createOscillator()
    const gainNode = ctx.createGain()
    oscillator.type = type
    oscillator.frequency.value = frequency
    gainNode.gain.value = safeVolume
    gainNode.gain.exponentialRampToValueAtTime(0.001, ctx.currentTime + duration)

    oscillator.connect(gainNode).connect(ctx.destination)
    oscillator.start()
    oscillator.stop(ctx.currentTime + duration)
  }

  const sounds = {
    confirm: () => playBeep({ frequency: 880, duration: 0.1, volume: 0.2 }),
    alert: () => playBeep({ frequency: 440, duration: 0.3, type: 'square', volume: 0.4 }),
    error: () => playBeep({ frequency: 220, duration: 0.5, type: 'sawtooth', volume: 0.3 }),
    click: () => playBeep({ frequency: 1000, duration: 0.05, volume: 0.1 })
  }
  return { playBeep, sounds }
}

4.3 Audio Visualization

// composables/useAudioVisualization.ts
export function useAudioVisualization() {
  const { audioContext, initialize } = useAudioContext()
  let analyser: AnalyserNode | null = null
  let dataArray: Uint8Array | null = null

  async function setupAnalyser(source: AudioNode) {
    await initialize()
    const ctx = audioContext.value
    if (!ctx) return
    analyser = ctx.createAnalyser()
    analyser.fftSize = 256
    dataArray = new Uint8Array(analyser.frequencyBinCount)
    source.connect(analyser)
  }

  function getFrequencyData(): Uint8Array | null {
    if (!analyser || !dataArray) return null
    analyser.getByteFrequencyData(dataArray)
    return dataArray
  }

  return { setupAnalyser, getFrequencyData }
}

4.4 Spatial Audio for 3D HUD

// composables/useSpatialAudio.ts
export function useSpatialAudio() {
  const { audioContext, initialize } = useAudioContext()
  let panner: PannerNode | null = null

  async function createSpatialSource(position: SpatialAudioPosition) {
    await initialize()
    const ctx = audioContext.value
    if (!ctx) return null
    panner = ctx.createPanner()
    panner.panningModel = 'HRTF'
    panner.distanceModel = 'inverse'
    setPosition(position)
    return panner
  }

  function setPosition(pos: SpatialAudioPosition) {
    if (!panner) return
    panner.positionX.value = pos.x
    panner.positionY.value = pos.y
    panner.positionZ.value = pos.z
  }

  return { createSpatialSource, setPosition }
}

4.5 Microphone Input

// composables/useMicrophone.ts
export function useMicrophone() {
  const { audioContext, initialize } = useAudioContext()
  const stream = ref<MediaStream | null>(null)
  const isListening = ref(false)
  const error = ref<string | null>(null)

  async function startListening() {
    try {
      await initialize()
      stream.value = await navigator.mediaDevices.getUserMedia({
        audio: { echoCancellation: true, noiseSuppression: true, autoGainControl: true }
      })
      isListening.value = true
      return stream.value
    } catch (err) {
      error.value = err instanceof Error ? err.message : 'Microphone access denied'
      return null
    }
  }

  function stopListening() {
    stream.value?.getTracks().forEach(track => track.stop())
    stream.value = null
    isListening.value = false
  }

  onUnmounted(() => stopListening())

  return { stream: readonly(stream), isListening: readonly(isListening), error: readonly(error), startListening, stopListening }
}

5. Implementation Workflow (TDD)

Step 1: Write Failing Test First

// tests/composables/useHUDSounds.test.ts
import { describe, it, expect, vi, beforeEach } from 'vitest'
import { useHUDSounds } from '~/composables/useHUDSounds'

// Mock AudioContext nodes
const mockOscillator = { connect: vi.fn(), start: vi.fn(), stop: vi.fn(), frequency: { value: 440 } }
const mockGainNode = { connect: vi.fn(), gain: { value: 1, exponentialRampToValueAtTime: vi.fn() } }
const mockAudioContext = {
  state: 'running', currentTime: 0, destination: {},
  createOscillator: vi.fn(() => mockOscillator),
  createGain: vi.fn(() => mockGainNode),
  resume: vi.fn(), close: vi.fn()
}
vi.stubGlobal('AudioContext', vi.fn(() => mockAudioContext))

describe('useHUDSounds', () => {
  beforeEach(() => vi.clearAllMocks())

  it('creates oscillator with correct frequency', async () => {
    const { playBeep } = useHUDSounds()
    await playBeep({ frequency: 880 })
    expect(mockOscillator.frequency.value).toBe(880)
  })

  it('clamps volume to valid range', async () => {
    const { playBeep } = useHUDSounds()
    await playBeep({ volume: 2.5 })
    expect(mockGainNode.gain.value).toBeLessThanOrEqual(1)
  })

  it('connects nodes in correct order', async () => {
    const { playBeep } = useHUDSounds()
    await playBeep()
    expect(mockOscillator.connect).toHaveBeenCalledWith(mockGainNode)
    expect(mockGainNode.connect).toHaveBeenCalledWith(mockAudioContext.destination)
  })
})

Step 2: Implement Minimum to Pass

// composables/useHUDSounds.ts
export function useHUDSounds() {
  // Implementation from section 4.2
  // Only add features that tests require
}

Step 3: Refactor Following Patterns

After tests pass, refactor to:

• Extract shared audio context logic
• Add proper TypeScript types
• Implement cleanup on unmount

Step 4: Run Full Verification

# Run all audio-related tests
npm test -- --grep "audio|sound|HUD"

# Check types
npm run typecheck

# Verify no memory leaks in browser
npm run dev  # Test manually with DevTools Memory tab

6. Performance Patterns

6.1 AudioWorklet for Processing

// ✅ Good: Use AudioWorklet for DSP (runs on audio thread)
class NoiseGateProcessor extends AudioWorkletProcessor {
  process(inputs: Float32Array[][], outputs: Float32Array[][]) {
    for (let ch = 0; ch < inputs[0].length; ch++) {
      for (let i = 0; i < inputs[0][ch].length; i++) {
        outputs[0][ch][i] = Math.abs(inputs[0][ch][i]) > 0.01 ? inputs[0][ch][i] : 0
      }
    }
    return true
  }
}
registerProcessor('noise-gate', NoiseGateProcessor)

// ❌ Bad: ScriptProcessorNode (deprecated, blocks main thread)

6.2 Buffer Pooling

// ✅ Good: Reuse audio buffers
class AudioBufferPool {
  private pool: AudioBuffer[] = []
  constructor(ctx: AudioContext, size: number, length: number) {
    for (let i = 0; i < size; i++) {
      this.pool.push(ctx.createBuffer(2, length, ctx.sampleRate))
    }
  }
  acquire(): AudioBuffer | undefined { return this.pool.pop() }
  release(buffer: AudioBuffer) {
    for (let ch = 0; ch < buffer.numberOfChannels; ch++) {
      buffer.getChannelData(ch).fill(0)
    }
    this.pool.push(buffer)
  }
}

// ❌ Bad: Create new buffer each time
const buffer = ctx.createBuffer(2, 44100, 44100) // Allocates memory each call

6.3 Offline Rendering

// ✅ Good: Pre-render complex sounds
async function prerenderSound(): Promise<AudioBuffer> {
  const offlineCtx = new OfflineAudioContext(2, 44100, 44100)
  const osc = offlineCtx.createOscillator()
  const gain = offlineCtx.createGain()
  osc.connect(gain).connect(offlineCtx.destination)
  gain.gain.setValueAtTime(0, 0)
  gain.gain.linearRampToValueAtTime(1, 0.01)
  gain.gain.exponentialRampToValueAtTime(0.001, 1)
  osc.start(); osc.stop(1)
  return offlineCtx.startRendering()
}

// ❌ Bad: Generate complex sounds in real-time (multiple oscillators computed live)

6.4 Node Graph Optimization

// ✅ Good: Reuse master gain node
const masterGain = ctx.createGain()
masterGain.connect(ctx.destination)
function playSound(buffer: AudioBuffer) {
  const source = ctx.createBufferSource()
  source.buffer = buffer
  source.connect(masterGain)
  source.start()
}

// ❌ Bad: Create full chain for each sound (gain + compressor per play)

6.5 Memory Management

// ✅ Good: Disconnect and cleanup nodes
function playOneShot(buffer: AudioBuffer) {
  const source = ctx.createBufferSource()
  source.buffer = buffer
  source.connect(masterGain)
  source.onended = () => source.disconnect()
  source.start()
}

// ✅ Good: Limit concurrent sounds (max 8)
class SoundManager {
  private activeSources = new Set<AudioBufferSourceNode>()
  play(buffer: AudioBuffer) {
    if (this.activeSources.size >= 8) this.activeSources.values().next().value?.stop()
    const source = ctx.createBufferSource()
    source.buffer = buffer
    source.connect(masterGain)
    source.onended = () => { source.disconnect(); this.activeSources.delete(source) }
    this.activeSources.add(source)
    source.start()
  }
}

// ❌ Bad: Never cleanup - nodes stay in memory after playback
const source = ctx.createBufferSource()
source.connect(ctx.destination)
source.start()

7. Quality Standards

// ✅ Always require user gesture
button.addEventListener('click', async () => {
  await audioContext.resume()
  playSound()
})

// ✅ Respect user preferences
if (usePreferencesStore().preferences.soundEnabled) playBeep()

// ✅ Handle permission denial gracefully
try {
  await navigator.mediaDevices.getUserMedia({ audio: true })
} catch (err) {
  if (err.name === 'NotAllowedError') {
    showVisualFeedback('Microphone access required')
  }
}

8. Testing & Quality

describe('HUD Sounds', () => {
  it('validates volume bounds', async () => {
    const { playBeep } = useHUDSounds()
    await playBeep({ volume: 2 })  // Clamped to 1
    await playBeep({ volume: -1 }) // Clamped to 0
  })
})

9. Common Mistakes & Anti-Patterns

9.1 Critical Anti-Patterns

// ❌ Auto-play without user gesture - BLOCKED
onMounted(() => playSound())

// ✅ After user interaction
const handleClick = async () => { await audioContext.resume(); playSound() }

// ❌ Memory leak - no cleanup
const audioContext = new AudioContext()

// ✅ Proper cleanup
onUnmounted(() => audioContext.close())

// ❌ New context per sound - performance killer
function playSound() { const ctx = new AudioContext() }

// ✅ Reuse context
const ctx = new AudioContext()
function playSound() { /* reuse ctx */ }

10. Pre-Implementation Checklist

Phase 1: Before Writing Code

• Tests written for audio node creation and connections
• Tests written for volume clamping and validation
• Performance requirements identified (latency, concurrent sounds)
• AudioWorklet needed for DSP? Worklet file created
• Buffer pool size calculated for expected usage

Phase 2: During Implementation

• User gesture required for AudioContext initialization
• Audio context reused (not created per sound)
• Nodes disconnected in onended callbacks
• Volume bounds validated (0-1 range)
• Microphone permissions handled gracefully
• Error states provide visual feedback

Phase 3: Before Committing

• All audio tests pass: npm test -- --grep "audio"
• Type checking passes: npm run typecheck
• No memory leaks (tested in DevTools Memory tab)
• Audio context closed on component unmount
• Visual alternatives provided for accessibility
• Sound can be disabled via user preferences
• Volume respects system preferences

11. Summary

Web Audio API for JARVIS: Initialize after user gesture, cleanup on unmount, handle permission denials, provide visual alternatives. See references/advanced-patterns.md

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