Technical Details

Sound Design

How Pico communicates through sound

PICO Sound Bank Guide

Document Type: Technical Implementation Guide
Version: 1.0
Date: December 5, 2025
Status: Production-Ready
Purpose: Complete guide for creating and managing PICO's non-verbal sound communication system

Table of Contents

  1. Overview
  2. Sound Bank Structure
  3. Technical Specifications
  4. Sound Design Philosophy
  5. Creation Methods
  6. Required Sounds List
  7. Processing Workflow
  8. Testing & Quality Control
  9. Integration Guide
  10. Sound Mapping Configuration

Overview

PICO's personality is expressed entirely through non-verbal sounds. This guide provides comprehensive instructions for creating a complete sound library that makes PICO feel alive, expressive, and emotionally engaging.

Goal: Create 20-30 high-quality sound effects that convey emotion and personality without using human speech.

Design Philosophy: PICO is a non-verbal pet companion that communicates through pre-recorded sound effects (.wav files) like chirps, purrs, and whistles - similar to R2-D2, Wall-E, or Pokemon.

Sound Bank Structure

Complete Directory Structure

pico_robot/
├── assets/
│   └── sounds/
│       ├── README.md                    # Sound Bank documentation
│       ├── ATTRIBUTION.md               # Source credits for sounds
│       │
│       ├── emotional/                   # Emotional expression sounds
│       │   ├── happy_chirp_01.wav      # Primary happiness sound
│       │   ├── happy_chirp_02.wav      # Variation 1
│       │   ├── happy_chirp_03.wav      # Variation 2
│       │   ├── curious_hum_01.wav      # Questioning/investigation
│       │   ├── curious_hum_02.wav      # Variation
│       │   ├── sad_whimper_01.wav      # Disappointment
│       │   ├── excited_whistle_01.wav  # High energy
│       │   ├── excited_whistle_02.wav  # Variation
│       │   ├── loved_purr_01.wav       # Contentment (continuous)
│       │   ├── sleepy_yawn_01.wav      # Low energy/tired
│       │   ├── playful_giggle_01.wav   # During active play
│       │   ├── surprised_beep_01.wav   # Unexpected event
│       │   └── confused_warble_01.wav  # Didn't understand
│       │
│       ├── reactions/                   # System response sounds
│       │   ├── greeting_beep.wav       # Hello sound
│       │   ├── greeting_melody.wav     # Morning greeting variation
│       │   ├── acknowledgment_chirp.wav # "I heard you"
│       │   ├── success_ding.wav        # Command successful
│       │   ├── error_buzz.wav          # Something went wrong
│       │   ├── listening_bing.wav      # Wake word detected
│       │   ├── goodbye_chime.wav       # Farewell sound
│       │   ├── notification_ping.wav   # General alert
│       │   └── alert_urgent.wav        # Important notification
│       │
│       ├── ambient/                     # Background/continuous sounds
│       │   ├── startup_beep.wav        # Power-on sequence
│       │   ├── thinking_hum.wav        # Processing indicator
│       │   ├── idle_breathing.wav      # Subtle life presence
│       │   ├── working_hum.wav         # During long tasks
│       │   ├── night_lullaby.wav       # Bedtime sound
│       │   └── morning_chirp.wav       # Time-based greeting
│       │
│       └── test/                        # Test and calibration sounds
│           ├── test_tone_440hz.wav     # Calibration tone
│           ├── test_sweep.wav          # Frequency sweep test
│           └── volume_reference.wav    # Volume calibration

Naming Conventions

Pattern: emotion_type_variation.wav

Examples:

  • happy_chirp_01.wav - Happy emotion, chirp type, variation 1
  • curious_hum_01.wav - Curious emotion, hum type, variation 1
  • success_ding.wav - Success reaction, ding type (no variation number if only one)

Rules:

  • All lowercase
  • Underscore separated
  • No spaces or special characters
  • Variation numbers: 01, 02, 03 (zero-padded)
  • Descriptive type (chirp, hum, beep, ding, buzz, whistle, purr, etc.)

Technical Specifications

Required Audio Format

All sounds MUST meet these specifications:

| Property | Value | Reason | |----------|-------|--------| | Format | WAV (uncompressed) | No decoding overhead, instant playback | | Sample Rate | 16kHz | Optimal for ESP32, good quality, low file size | | Bit Depth | 16-bit | Standard quality, efficient storage | | Channels | Mono | Single speaker, reduces file size by 50% | | Duration | 0.3 - 3.0 seconds | Quick responses, not too short/long | | Max File Size | ~100KB per sound | Memory constraints on ESP32 |

Why These Specs?

  • 16kHz: The ESP32-S3 can handle higher, but 16kHz is the sweet spot for:

    • Clear sound quality for beeps/chirps
    • Efficient memory usage (3 sec @ 16kHz = ~96KB)
    • Fast playback startup

  • Mono: PICO has one speaker, stereo is wasted

  • WAV format: No MP3 decoding lag, instant response

Sound Design Philosophy

What Makes a Good PICO Sound?

PICO sounds should be:

  1. Emotionally Clear: Listeners should immediately understand the emotion
  2. Non-Human: Should not sound like words or human vocalization
  3. Endearing: Cute, lovable, not annoying or harsh
  4. Distinctive: Each sound should be recognizable
  5. Varied: Multiple variations of common sounds prevent monotony

Inspiration Sources

  • R2-D2 (Star Wars): Electronic beeps with personality
  • Wall-E: Expressive robotic sounds with emotional range
  • Pokemon: Simple syllable-based communication
  • BB-8: Rolling beeps and excited chirps
  • Portal Turrets: Friendly mechanical sounds

Emotional Sound Characteristics

| Emotion | Pitch | Speed | Complexity | Example Pattern | |---------|-------|-------|------------|-----------------| | Happy | High, rising | Fast | Simple | ↗️ "bee-beep!" | | Sad | Low, falling | Slow | Simple | ↘️ "wooo-omp" | | Curious | Medium, wavering | Medium | Rising question | ↗️? "bee?-oop?" | | Excited | Very high | Very fast | Multiple notes | ↗️↗️↗️ "beepbeepbeep!" | | Confused | Wobbly, uncertain | Variable | Dissonant | ~~ "woo-blee-orp?" | | Loved/Content | Low, rumbling | Slow, steady | Warm, continuous | ~~~~ "purrrr" | | Sleepy | Low, fading | Very slow | Descending | ↘️... "yaaawwwn" |

Creation Methods

Method 1: Software Synthesis (Easiest)

Tools:

  • Bfxr (https://www.bfxr.net/) - Free, web-based, perfect for game sounds
  • ChipTone (https://sfbgames.itch.io/chiptone) - Retro chiptune generator
  • Audacity - Free audio editor with tone generator

Bfxr Workflow for Happy Chirp:

1. Open Bfxr in browser
2. Click "Pickup/Coin" preset
3. Adjust parameters:
   - Base Frequency: 800-1000 Hz
   - Slide: +0.3 (rising pitch)
   - Duration: 0.2-0.4 seconds
   - Wave Type: Square or Sawtooth
4. Preview until it sounds cheerful
5. Export as WAV
6. Post-process in Audacity (see Processing Workflow)

Audacity Tone Generator for Beeps:

1. Generate > Tone
2. Waveform: Sine (smooth) or Square (electronic)
3. Frequency: 440-880 Hz
4. Amplitude: 0.5
5. Duration: 0.3 seconds
6. Apply envelope (Attack: 0.01s, Decay: 0.02s)

Method 2: Voice Modulation (Most Expressive)

Tools:

  • Audacity with pitch shift
  • Adobe Audition (paid, but powerful)
  • Your voice + effects

Workflow:

1. Record yourself making sounds:
   - "Bee-boop!" (happy)
   - "Hmmmm?" (curious)
   - "Awwww" (sad)
   - "Wheeee!" (excited)

2. In Audacity:
   - Effect > Change Pitch: +800-1200% (makes it robotic/cute)
   - Effect > Change Speed: +25-50% (makes it snappier)
   - Effect > Equalization: Boost 800-2000Hz (electronic tone)
   - Effect > Reverb: Small room, 10% (adds space)

3. Trim to 0.5-1.5 seconds
4. Normalize to -3dB

This method creates the most "alive" sounds because they have natural human emotional inflection, just pitched up to sound robotic.

Method 3: Sampling & Editing (Professional)

Sources:

  • Freesound.org - Huge library of Creative Commons sounds
  • Zapsplat.com - Free sound effects
  • BBC Sound Effects - Public domain library
  • Field recording - Record real objects

Search terms:

  • "robot beep"
  • "electronic chirp"
  • "game pickup"
  • "toy sound"
  • "notification"

Workflow:

1. Download promising sounds
2. Import to Audacity
3. Cut to best 1-2 seconds
4. Remove background noise (Effect > Noise Reduction)
5. Adjust pitch/speed to fit PICO's character
6. Apply filters:
   - High-pass filter @ 200Hz (remove rumble)
   - Boost 1-2kHz (clarity)
7. Normalize to -3dB
8. Export as WAV

Method 4: Hybrid Approach (Recommended)

Combine methods for best results:

Base Sound (Bfxr) + Voice Expression (Audacity) + Polish (Effects)

Example - Creating "Loved Purr":
1. Generate low sine wave in Bfxr (100-200Hz)
2. Record yourself making "prrrr" sound
3. Layer them in Audacity (50% each)
4. Add slight vibrato (Effect > Wahwah, Frequency: 4Hz)
5. Result: Warm, mechanical purr with organic feel

Required Sounds List

Priority 1: Essential Sounds (Must Have)

Emotional Expressions:

1. happy_chirp_01.wav       - Primary happiness sound
2. happy_chirp_02.wav       - Variation to avoid repetition
3. curious_hum_01.wav       - Questioning/investigation
4. sad_whimper_01.wav       - Disappointment/sadness
5. excited_whistle_01.wav   - High energy excitement
6. loved_purr_01.wav        - Contentment when petted

System Responses:

7. listening_bing.wav       - Wake word detected
8. acknowledgment_chirp.wav - "I heard you"
9. success_ding.wav         - Command executed successfully
10. error_buzz.wav          - Something went wrong

Ambient:

11. startup_beep.wav        - Power on sequence
12. thinking_hum.wav        - Processing indicator

Priority 2: Enhanced Personality (Recommended)

More Emotions:

13. sleepy_yawn_01.wav      - Low battery/idle too long
14. confused_warble.wav     - Didn't understand
15. surprised_beep.wav      - Unexpected face detected
16. greeting_melody.wav     - Morning greeting

Interactions:

17. playful_giggle.wav      - During active interaction
18. goodbye_chime.wav       - User leaving
19. notification_ping.wav   - Alert sound
20. alert_urgent.wav        - Important notification

Priority 3: Advanced Features (Optional)

Contextual:

21. morning_chirp.wav       - Time-based greeting
22. night_lullaby.wav       - Bedtime sound
23. working_hum.wav         - During long tasks
24. idle_breathing.wav      - Subtle life presence

Processing Workflow

Universal Processing Pipeline

Every sound should go through these steps in Audacity:

Step 1: Import & Trim

1. File > Import > Audio
2. Select the best 0.5-3 second segment
3. Edit > Remove Audio or Trim Audio

Step 2: Noise Reduction (if recorded)

1. Select silent part (if any)
2. Effect > Noise Reduction > Get Noise Profile
3. Select all (Ctrl+A)
4. Effect > Noise Reduction > OK (Reduction: 12dB)

Step 3: EQ (Frequency Shaping)

Effect > Filter Curve EQ:
- High-pass at 200Hz (remove rumble)
- Gentle boost at 800-2000Hz (clarity and presence)
- Roll-off above 8kHz (we're at 16kHz sample rate, focus on mids)

Presets:
- Happy sounds: Boost 1-2kHz (bright)
- Sad sounds: Boost 200-400Hz (warm, low)
- Electronic sounds: Notch at 1kHz, boost 2-4kHz (metallic)

Step 4: Dynamics

Effect > Compressor:
- Threshold: -12dB
- Ratio: 3:1
- Attack: 0.01s
- Release: 0.2s

This makes quiet parts louder and prevents clipping.

Step 5: Normalization

Effect > Normalize:
- Normalize peak amplitude to: -3.0 dB
- ✅ Normalize stereo channels independently (if stereo)

This ensures consistent volume across all sounds.

Step 6: Convert to Mono

Tracks > Mix > Mix Stereo Down to Mono

Step 7: Resample to 16kHz

Tracks > Resample:
- New sample rate: 16000 Hz

Step 8: Export

File > Export > Export Audio:
- Format: WAV (Microsoft) signed 16-bit PCM
- Filename: descriptive_name.wav

Testing & Quality Control

Listening Tests

Before finalizing sounds, test them:

  1. Emotional Clarity Test

    • Play sound without context
    • Ask: "What emotion is this?"
    • Should be immediately obvious

  2. Volume Consistency Test

    • Play all sounds in sequence
    • All should be roughly same loudness
    • Use loudness meter (Audacity: Analyze > Contrast)

  3. Speaker Test

    • Test on small speaker (similar to PICO's)
    • Sounds that are too bass-heavy won't work
    • Laptop speakers are good reference

  4. Repetition Test

    • Play same sound 10 times
    • Does it get annoying? (if yes, redesign)
    • Is there variation if applicable?

  5. Context Test

    • Play in sequence: happy > sad > curious
    • Transitions should feel natural
    • Each should be distinct

Technical Verification

# verify_sounds.py
import soundfile as sf
import os

def verify_sound_files(sounds_dir='assets/sounds/'):
    """Verify all sound files meet specifications"""
    
    issues = []
    
    for root, dirs, files in os.walk(sounds_dir):
        for file in files:
            if file.endswith('.wav'):
                path = os.path.join(root, file)
                
                try:
                    data, samplerate = sf.read(path)
                    duration = len(data) / samplerate
                    channels = 1 if len(data.shape) == 1 else data.shape[1]
                    
                    # Check specifications
                    if samplerate != 16000:
                        issues.append(f"❌ {file}: Wrong sample rate ({samplerate}Hz, should be 16000Hz)")
                    
                    if channels != 1:
                        issues.append(f"❌ {file}: Not mono ({channels} channels)")
                    
                    if duration > 3.0:
                        issues.append(f"⚠️ {file}: Too long ({duration:.2f}s, max 3.0s)")
                    
                    if duration < 0.2:
                        issues.append(f"⚠️ {file}: Very short ({duration:.2f}s)")
                    
                    # Check for clipping
                    if abs(data).max() > 0.99:
                        issues.append(f"⚠️ {file}: Possible clipping detected")
                    
                    # Check for silence
                    if abs(data).max() < 0.01:
                        issues.append(f"❌ {file}: Too quiet or silent")
                    
                    if not issues:
                        print(f"✅ {file}: OK ({duration:.2f}s, {samplerate}Hz)")
                        
                except Exception as e:
                    issues.append(f"❌ {file}: Error reading file - {e}")
    
    if issues:
        print("\n⚠️ Issues Found:")
        for issue in issues:
            print(issue)
    else:
        print("\n✅ All sound files verified!")

Integration Guide

File Organization

Place all sound files in the appropriate category folders as shown in the Sound Bank Structure section above.

Testing in Simulation

# test_sounds.py
from sound_bank import SoundBank
import time

def test_all_sounds():
    """Play all sounds for review"""
    sb = SoundBank('assets/sounds/')
    
    print("🎵 Testing PICO Sound Bank\n")
    
    categories = sb.get_available_sounds()
    
    for category, sounds in categories.items():
        print(f"\n=== {category.upper()} ===")
        for sound in sorted(sounds):
            print(f"\nPlaying: {sound}")
            input("Press Enter to play...")
            sb.play(sound)
            time.sleep(2)
    
    print("\n✅ Sound bank test complete!")

if __name__ == "__main__":
    test_all_sounds()

Adding New Sounds

  1. Create sound following this guide
  2. Save to appropriate category folder
  3. Restart robot or call sound_bank.load_all_sounds()
  4. Test in context
  5. Document in sound_bank.py mapping if needed

Sound Mapping Configuration

emotion_sound_map.json

{
  "emotions": {
    "happy": {
      "sounds": ["happy_chirp_01", "happy_chirp_02", "happy_chirp_03"],
      "selection": "random_variation",
      "category": "emotional"
    },
    "curious": {
      "sounds": ["curious_hum_01", "curious_hum_02"],
      "selection": "random_variation",
      "category": "emotional"
    },
    "sad": {
      "sounds": ["sad_whimper_01"],
      "selection": "single",
      "category": "emotional"
    },
    "excited": {
      "sounds": ["excited_whistle_01", "excited_whistle_02"],
      "selection": "random_variation",
      "category": "emotional"
    },
    "loved": {
      "sounds": ["loved_purr_01"],
      "selection": "continuous",
      "category": "emotional"
    },
    "sleepy": {
      "sounds": ["sleepy_yawn_01"],
      "selection": "single",
      "category": "emotional"
    }
  },
  "reactions": {
    "greeting": {
      "sounds": ["greeting_beep", "greeting_melody"],
      "selection": "context_based",
      "category": "reactions"
    },
    "acknowledgment": {
      "sounds": ["acknowledgment_chirp"],
      "selection": "single",
      "category": "reactions"
    },
    "success": {
      "sounds": ["success_ding"],
      "selection": "single",
      "category": "reactions"
    },
    "error": {
      "sounds": ["error_buzz"],
      "selection": "single",
      "category": "reactions"
    }
  },
  "ambient": {
    "startup": {
      "sounds": ["startup_beep"],
      "selection": "single",
      "category": "ambient"
    },
    "thinking": {
      "sounds": ["thinking_hum"],
      "selection": "looping",
      "category": "ambient"
    }
  }
}

Resources

Free Sound Creation Tools

  • Bfxr: https://www.bfxr.net/
  • ChipTone: https://sfbgames.itch.io/chiptone
  • Audacity: https://www.audacityteam.org/
  • LMMS: https://lmms.io/ (music production)

Free Sound Libraries

  • Freesound: https://freesound.org/
  • Zapsplat: https://www.zapsplat.com/
  • BBC Sound Effects: https://sound-effects.bbcrewind.co.uk/
  • Sonniss GDC: https://sonniss.com/gameaudiogdc (annual free pack)

Learning Resources

  • YouTube: "How to make robot sounds"
  • YouTube: "Chiptune sound design tutorial"
  • Game Audio 101: Tutorials on game sound design
  • r/AudioPost: Reddit community for audio questions

Quick Start Checklist

Ready to create PICO's voice? Follow this:

  • [ ] Install Audacity (or use Bfxr web app)
  • [ ] Create Priority 1 sounds (12 essential sounds)
  • [ ] Process all sounds through standard workflow
  • [ ] Verify with verification script
  • [ ] Test in simulation
  • [ ] Create variations of frequently used sounds
  • [ ] Add Priority 2 sounds for more personality
  • [ ] Document any custom sounds in sound_bank.py
  • [ ] Backup sound library

Conclusion

Creating PICO's sound bank is where its personality truly comes alive. Take your time with this - good sounds make the difference between a robot that feels mechanical and one that feels like a living companion.

Remember: PICO doesn't need to speak words to communicate. A well-crafted chirp can convey more emotion and personality than any sentence ever could.

Happy sound designing! 🎵🤖✨