diff --git a/PIPER_TTS_INTEGRATION.md b/PIPER_TTS_INTEGRATION.md
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+# Piper TTS Integration Summary
+
+## Overview
+
+Successfully integrated Piper TTS as an alternative text-to-speech engine alongside Kokoro TTS, giving users the ability to choose between two engines with different strengths.
+
+## What Was Added
+
+### Backend Components
+
+1. **PiperTTSService** (`backend/services/piper_tts_service.py`)
+   - Handles Piper TTS synthesis with pitch control
+   - Supports pitch shifting from -12 to +12 semitones per character
+   - Automatic voice model downloading
+   - Audio effects processing (pitch and speed)
+
+2. **UnifiedTTSService** (`backend/services/unified_tts_service.py`)
+   - Manages multiple TTS engines (Kokoro and Piper)
+   - Runtime engine switching
+   - Unified API for both engines
+   - Handles engine-specific features (pitch control for Piper)
+
+3. **New API Endpoints** (in `backend/main.py`)
+   - `GET /api/tts/engines` - List available engines and current selection
+   - `POST /api/tts/engines` - Switch active TTS engine
+   - `GET /api/tts/voices` - Get available voices for all engines
+   - Updated `POST /api/tts` to support `pitch_adjustments` parameter
+
+4. **Installation Script** (`backend/install_piper.sh`)
+   - Automated Piper TTS installation for macOS/Linux
+   - Detects OS and architecture
+   - Installs to `/usr/local/bin`
+
+### Frontend Components
+
+1. **API Client Functions** (`frontend/src/api/tts.ts`)
+   - `getEngines()` - Fetch available engines
+   - `setEngine(engine)` - Switch active engine
+   - `getVoices()` - Get voices for all engines
+   - TypeScript interfaces for engine data
+
+2. **UI Components** (`frontend/src/components/VoiceAssignmentSection.tsx`)
+   - Engine selector buttons (Kokoro vs Piper)
+   - Dynamic voice loading based on selected engine
+   - Visual feedback for active engine
+   - Pitch control capability notice for Piper
+
+### Documentation
+
+1. **Backend README** (`backend/README.md`)
+   - Multi-engine setup instructions
+   - Engine switching examples
+   - Pitch control documentation
+
+2. **Piper TTS Guide** (`backend/PIPER_TTS_GUIDE.md`)
+   - Comprehensive installation guide
+   - Available voices documentation
+   - Pitch adjustment guidelines
+   - Usage examples and best practices
+   - Troubleshooting section
+
+3. **Integration Summary** (this file)
+
+## Engine Comparison
+
+| Feature | Kokoro TTS | Piper TTS |
+|---------|------------|-----------|
+| **Quality** | High | Medium-High |
+| **Speed** | Medium | Fast |
+| **Voices** | 54 voices, 9 languages | 5+ English voices |
+| **Pitch Control** | ❌ No | ✅ Yes (-12 to +12 semitones) |
+| **Model Size** | ~500MB | ~10-50MB per voice |
+| **Memory Usage** | Higher | Lower |
+| **Languages** | 9 languages | English (more available) |
+
+## How to Use
+
+### Backend Setup
+
+1. **Install Piper TTS** (optional):
+   ```bash
+   cd backend
+   ./install_piper.sh
+   ```
+
+2. **Set default engine** (optional):
+   ```bash
+   # In backend/.env
+   TTS_ENGINE=piper  # or kokoro (default)
+   ```
+
+3. **Install Python dependencies**:
+   ```bash
+   pip install -r requirements.txt
+   ```
+
+### Frontend Usage
+
+1. **Select Engine**: In the Voice Assignment screen, click either "Kokoro TTS" or "Piper TTS" button
+2. **Choose Voices**: Voice dropdown updates automatically with engine-specific voices
+3. **Generate**: Audio is generated using the selected engine
+
+### API Usage
+
+**Switch Engine:**
+```bash
+curl -X POST http://localhost:8000/api/tts/engines \
+  -H "Content-Type: application/json" \
+  -d '{"engine": "piper"}'
+```
+
+**Generate with Pitch Control (Piper only):**
+```bash
+curl -X POST http://localhost:8000/api/tts \
+  -H "Content-Type: application/json" \
+  -d '{
+    "text": "Alice: Hello!\nBob: Hi there!",
+    "lang": "a",
+    "roles": [
+      {"id": "Alice", "voice": "en_US-amy-medium"},
+      {"id": "Bob", "voice": "en_US-lessac-medium"}
+    ],
+    "pitch_adjustments": [
+      {"id": "Alice", "pitch": 3},
+      {"id": "Bob", "pitch": -2}
+    ]
+  }' \
+  --output audiobook.wav
+```
+
+## Pitch Control Guidelines
+
+When using Piper TTS, you can adjust pitch per character:
+
+- **+12 semitones**: One octave higher (very high-pitched)
+- **+6 semitones**: Noticeably higher (child-like)
+- **+3 semitones**: Slightly higher (feminine adjustment)
+- **0 semitones**: Original voice (no change)
+- **-3 semitones**: Slightly lower (masculine adjustment)
+- **-6 semitones**: Noticeably lower (deep voice)
+- **-12 semitones**: One octave lower (very deep)
+
+**Recommended ranges:**
+- Female characters: +2 to +5
+- Male characters: -2 to -5
+- Children: +5 to +8
+- Elderly/deep voices: -4 to -8
+
+## Testing
+
+Run the engine selection test:
+```bash
+cd backend
+python test_engine_selection.py
+```
+
+## Files Modified/Created
+
+### Backend
+- ✅ `backend/services/piper_tts_service.py` (new)
+- ✅ `backend/services/unified_tts_service.py` (new)
+- ✅ `backend/main.py` (modified - added endpoints)
+- ✅ `backend/requirements.txt` (modified - added piper-tts, pydub)
+- ✅ `backend/.env.example` (modified - added TTS_ENGINE)
+- ✅ `backend/README.md` (modified - added multi-engine docs)
+- ✅ `backend/PIPER_TTS_GUIDE.md` (new)
+- ✅ `backend/install_piper.sh` (new)
+- ✅ `backend/test_engine_selection.py` (new)
+
+### Frontend
+- ✅ `frontend/src/api/tts.ts` (modified - added engine functions)
+- ✅ `frontend/src/components/VoiceAssignmentSection.tsx` (modified - added engine selector)
+
+### Documentation
+- ✅ `.kiro/specs/text-to-audiobook/tasks.md` (modified - added task 26)
+- ✅ `PIPER_TTS_INTEGRATION.md` (new - this file)
+
+## Git Commits
+
+1. **feat: Add Piper TTS integration with pitch control support** (bfdcc94)
+   - Backend services and API endpoints
+   - Installation script and documentation
+
+2. **feat: Add TTS engine selector UI in frontend** (c310f11)
+   - Frontend UI components
+   - API client functions
+
+## Next Steps (Optional Enhancements)
+
+1. **Pitch Control UI**: Add pitch sliders in the frontend for Piper engine
+2. **Voice Previews**: Update preview functionality to work with Piper voices
+3. **More Piper Voices**: Add support for additional Piper voice models
+4. **Coqui TTS**: Integrate Coqui XTTS as a third engine option
+5. **Voice Cloning**: Add voice cloning capabilities with Piper/Coqui
+
+## Notes
+
+- Piper TTS requires separate installation (not included in Python packages)
+- Voice models are downloaded automatically on first use
+- Kokoro remains the default engine for backward compatibility
+- Both engines can coexist and be switched at runtime
+- Pitch control is only available with Piper TTS
+
+## Support
+
+For issues or questions:
+- See `backend/PIPER_TTS_GUIDE.md` for detailed Piper documentation
+- See `backend/README.md` for general backend setup
+- Check troubleshooting sections in both guides
diff --git a/backend/test_engine_selection.py b/backend/test_engine_selection.py
new file mode 100644
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+++ b/backend/test_engine_selection.py
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+"""
+Test script for TTS engine selection functionality.
+"""
+import asyncio
+import sys
+from services.unified_tts_service import UnifiedTTSService
+
+
+async def test_engine_selection():
+    """Test switching between TTS engines."""
+    print("Testing TTS Engine Selection\n" + "="*50)
+    
+    # Initialize service
+    print("\n1. Initializing UnifiedTTSService...")
+    tts = UnifiedTTSService()
+    print(f"   Default engine: {tts.engine_name}")
+    
+    # Get available engines
+    print("\n2. Getting available engines...")
+    engines = tts.get_available_engines()
+    print(f"   Available: {engines}")
+    
+    # Get available voices
+    print("\n3. Getting available voices...")
+    voices = tts.get_available_voices()
+    for engine, voice_list in voices.items():
+        print(f"   {engine}: {len(voice_list)} voices")
+        if voice_list:
+            print(f"      Examples: {voice_list[:3]}")
+    
+    # Test switching to Piper
+    print("\n4. Switching to Piper engine...")
+    try:
+        tts.set_engine('piper')
+        print(f"   Current engine: {tts.engine_name}")
+    except Exception as e:
+        print(f"   ⚠️  Error: {e}")
+        print("   Note: Piper may not be installed. Run ./install_piper.sh")
+    
+    # Switch back to Kokoro
+    print("\n5. Switching back to Kokoro engine...")
+    tts.set_engine('kokoro')
+    print(f"   Current engine: {tts.engine_name}")
+    
+    # Test invalid engine
+    print("\n6. Testing invalid engine...")
+    try:
+        tts.set_engine('invalid')
+        print("   ❌ Should have raised error!")
+    except ValueError as e:
+        print(f"   ✓ Correctly rejected: {e}")
+    
+    print("\n" + "="*50)
+    print("✓ Engine selection tests completed!")
+
+
+if __name__ == "__main__":
+    asyncio.run(test_engine_selection())