🔊 Sound in Unreal

Audio in Unreal Engine

Unreal Engine provides a comprehensive audio system that handles everything from simple sound effects to complex, procedural audio compositions. Understanding the audio pipeline helps you create rich soundscapes that respond to gameplay.

The Audio Pipeline

Sound in Unreal follows a clear path from source to speaker:

1. Sound Wave: The raw audio file imported into Unreal
2. Sound Asset: Sound Cue, MetaSound, or direct Sound Wave reference
3. Audio Component: The component that plays the sound on an Actor
4. Sound Class: Categorization for volume control (Music, SFX, Voice)
5. Sound Mix: Master volume controls and effects
6. Output: Final audio sent to speakers/headphones

Figure: Audio flows from imported files through processing to final output.

Audio Engine Features

Unreal's audio engine provides powerful features:

Spatialization: 3D positioning of sounds in the game world. Sounds get louder as you approach, quieter as you move away, and pan left/right based on direction.

Attenuation: How sound volume decreases over distance. Configure falloff curves, maximum audible range, and occlusion (sounds muffled through walls).

Reverb: Environmental effects that simulate sound reflections in different spaces (cave echo, outdoor openness, small room).

Real-time Mixing: Adjust volumes, apply effects, and duck certain sounds based on gameplay state.

Procedural Audio: With MetaSounds, generate audio algorithmically rather than playing static files.

Audio Asset Types

Importing Audio Files

Before you can use sounds in Unreal, you need to import them. Understanding supported formats and import settings helps ensure your audio sounds great and performs well.

Supported Audio Formats

Unreal Engine supports several audio formats:

.WAV (Recommended):

• Uncompressed, highest quality
• Best for short sound effects
• Unreal compresses during cooking
• 16-bit or 24-bit, any sample rate (44.1kHz or 48kHz typical)

.OGG (Ogg Vorbis):

• Compressed, smaller file size
• Good for longer sounds (music, ambient loops)
• Slight quality loss vs WAV
• Streams well for large files

.FLAC:

• Lossless compression
• Smaller than WAV, same quality
• Good middle ground

Importing Sound Files

1. Prepare your audio file (WAV recommended, 44.1kHz or 48kHz)
2. In Content Browser, click Import or drag files directly
3. Navigate to your audio file(s) and select them
4. Choose destination folder in your project
5. Click Import

Unreal creates a Sound Wave asset for each imported file.

Sound Wave Properties

Double-click a Sound Wave to open its properties:

General:

• Duration: Length of the sound in seconds
• Sample Rate: Audio quality (44100 Hz typical)
• Channels: Mono (1) or Stereo (2)

Sound:

• Volume: Base volume multiplier (0.0 - 1.0+)
• Pitch: Playback speed/pitch multiplier
• Sound Class: Category assignment (SFX, Music, etc.)

Compression:

• Loading Behavior: How the sound loads into memory
• Compression Quality: Trade-off between size and quality

Figure: Sound Wave assets show waveform preview and configurable properties.

Loading Behavior Options

How a sound loads into memory affects both performance and memory usage:

Retain on Load: Sound stays in memory once loaded. Best for frequently used sounds (footsteps, gunshots).

Prime on Load: Loads async when level loads. Good for sounds needed soon after level start.

Load on Demand: Only loads when actually played. Saves memory but may cause slight delay on first play.

Stream: Streams from disk during playback. Essential for long sounds (music) to save memory. Small latency on start.

Mono vs Stereo

Mono (1 channel):

• Required for 3D spatialized sounds
• Engine can position in 3D space
• Use for: gunshots, footsteps, voice, most SFX

Stereo (2 channels):

• Fixed left/right channels
• Cannot be properly spatialized in 3D
• Use for: music, UI sounds, ambient beds

Most 3D sound effects should be mono. Unreal will spatialize mono sounds correctly. Stereo sounds played in 3D often sound wrong because the left/right channels don't move naturally.

Sound Cues vs MetaSounds

Unreal provides two systems for processing and enhancing audio beyond simple Sound Wave playback. Understanding when to use each helps you create better audio with less effort.

Sound Cues

Sound Cues are the traditional node-based sound processing system. They let you combine and modify Sound Waves visually.

Creating a Sound Cue:

1. Right-click in Content Browser
2. Select Sounds → Sound Cue
3. Name it (e.g., SC_Footstep)
4. Double-click to open the Sound Cue Editor

Common Sound Cue Nodes:

Figure: Sound Cue with random selection and pitch modulation.

MetaSounds

MetaSounds is Unreal's modern procedural audio system, introduced in UE5. It's more powerful than Sound Cues, enabling complex, generative audio.

Creating a MetaSound:

1. Right-click in Content Browser
2. Select Sounds → MetaSound Source
3. Name it (e.g., MS_Laser)
4. Double-click to open the MetaSound Editor

MetaSound Capabilities:

• Full audio DSP (Digital Signal Processing)
• Synthesizers and oscillators
• Runtime parameter control from Blueprints
• Complex routing and modulation
• Create sounds from scratch without audio files

When to Use Each

flowchart TD
    A["Need to process audio?"] -->|Simple randomization| B["Sound Cue"]
    A -->|Layer a few sounds| B
    A -->|Basic looping| B
    A -->|Runtime parameter control| C["MetaSound"]
    A -->|Procedural/synthesized| C
    A -->|Complex reactive audio| C
    A -->|Just play a sound| D["Sound Wave directly"]
    
    style B fill:#4CAF50,color:#fff
    style C fill:#9C27B0,color:#fff
    style D fill:#667eea,color:#fff
                

Figure: Decision tree for choosing audio asset type.

2D vs 3D Audio

Understanding the difference between 2D and 3D audio is crucial for creating immersive soundscapes. The wrong choice can break immersion or waste resources.

2D Audio (Non-Spatialized)

2D audio plays at consistent volume regardless of listener position. It has no sense of direction or distance.

Characteristics:

• Same volume everywhere in the level
• No left/right panning based on position
• No distance-based attenuation
• Plays "in the player's head"

Use 2D audio for:

• Background music
• UI sounds (button clicks, menu navigation)
• Voice-over narration
• Global announcements
• Ambient beds (constant background)

3D Audio (Spatialized)

3D audio is positioned in the game world. Volume and panning change based on the listener's position relative to the sound source.

Characteristics:

• Volume decreases with distance
• Pans left/right based on direction
• Can be occluded by geometry
• Requires mono source for proper spatialization

Use 3D audio for:

• Footsteps
• Gunshots and weapon sounds
• Environmental sounds (waterfalls, machinery)
• Character voices in world
• Pickup and interaction sounds

Figure: 2D audio is uniform; 3D audio attenuates with distance and direction.

Sound Attenuation

Attenuation controls how 3D sounds behave over distance. Create a Sound Attenuation asset:

1. Right-click in Content Browser
2. Select Sounds → Sound Attenuation
3. Name it (e.g., SA_Footsteps)
4. Configure distance and falloff settings

Key Attenuation Settings:

Inner Radius: Distance at which sound is at full volume. Within this radius, no attenuation.

Falloff Distance: Distance over which sound fades from full to silent. Larger = sound audible from farther away.

Attenuation Function:

• Linear: Even fade from inner to outer radius
• Logarithmic: Quick initial fade, then gradual (most realistic)
• Inverse: 1/distance relationship
• Natural Sound: Physically accurate (recommended)

Spatialization: How the sound is positioned in stereo/surround. Options include stereo panning and binaural (HRTF) for headphones.

Sound Classes and Mixes

Sound Classes categorize sounds for volume control:

1. Create Sound Class asset (Sounds → Sound Class)
2. Common classes: Master, Music, SFX, Voice, Ambient
3. Assign sounds to classes via their Sound Class property
4. Adjust class volume in settings menu (player controls)

Sound Mixes apply volume adjustments to classes:

1. Create Sound Mix asset (Sounds → Sound Mix)
2. Add Sound Class adjustments (volume, pitch multipliers)
3. Push/Pop mixes at runtime for dynamic changes

Example Mix Uses:

• Pause menu: Duck gameplay audio, keep UI sounds
• Dialogue: Lower music when characters speak
• Slow motion: Pitch down SFX

Figure: Sound Classes organize audio for separate volume control.

Hands-On: Audio Setup and Sound Cue

Let's put theory into practice by importing audio, creating a Sound Cue with variation, setting up Sound Classes, and testing both 2D and 3D audio playback.

Part 1: Prepare Audio Files

For this exercise, you'll need some sound files. You can:

• Use sounds from the Starter Content (if included in project)
• Download free sounds from Freesound.org or OpenGameArt.org
• Use the sounds included with Unreal's templates

Recommended sounds to gather:

• 3 footstep variations (WAV, mono, short ~0.2s each)
• 1 ambient loop (WAV or OGG, stereo, ~30s+)
• 1 UI click sound (WAV, mono or stereo, short)

Part 2: Import Sound Files

Step 1: Create Audio Folder

1. In Content Browser, create folder: Audio
2. Inside Audio, create subfolders:
   • Audio/SFX — Sound effects
   • Audio/Music — Background music
   • Audio/Ambient — Environmental sounds
   • Audio/UI — Interface sounds

Step 2: Import Footstep Sounds

1. Navigate to Audio/SFX
2. Click Import or drag files into the folder
3. Select your 3 footstep WAV files
4. Click Import
5. Rename them: SW_Footstep_01, SW_Footstep_02, SW_Footstep_03

Step 3: Verify Import Settings

1. Double-click one of the footstep Sound Waves
2. Verify it's Mono (for 3D spatialization)
3. Check the waveform preview looks correct
4. Click the Play button to preview the sound

Step 4: Import Ambient and UI Sounds

1. Import ambient loop to Audio/Ambient
2. Name it SW_Ambient_Forest (or appropriate name)
3. Import UI click to Audio/UI
4. Name it SW_UI_Click

Figure: Organized audio folder structure with naming convention.

Part 3: Create Sound Classes

Step 5: Create Sound Class Assets

1. In Content Browser, navigate to Audio folder
2. Right-click → Sounds → Sound Class
3. Name it SC_Master
4. Create additional Sound Classes:
   • SC_SFX
   • SC_Music
   • SC_Ambient
   • SC_UI

Step 6: Set Up Class Hierarchy

1. Double-click SC_SFX to open it
2. In Details panel, find Parent Sound Class
3. Set it to SC_Master
4. Repeat for SC_Music, SC_Ambient, SC_UI — all should have SC_Master as parent

Step 7: Assign Sounds to Classes

1. Open SW_Footstep_01
2. In Details, find Sound Class
3. Set it to SC_SFX
4. Repeat for all footstep sounds → SC_SFX
5. Set SW_Ambient_Forest → SC_Ambient
6. Set SW_UI_Click → SC_UI

Part 4: Create a Randomized Footstep Sound Cue

Step 8: Create the Sound Cue

1. Navigate to Audio/SFX
2. Right-click → Sounds → Sound Cue
3. Name it SC_Footstep
4. Double-click to open the Sound Cue Editor

Step 9: Add Wave Players

1. In the Sound Cue Editor, right-click the graph
2. Search for "Wave Player" and add one
3. Select the Wave Player node
4. In Details, set Sound Wave to SW_Footstep_01
5. Add two more Wave Players for Footstep_02 and Footstep_03

Step 10: Add Random Node

1. Right-click graph → Search "Random" → Add Random node
2. Connect all three Wave Player outputs to the Random node inputs
   • Drag from Wave Player output pin to Random input
   • Random node will add more inputs as needed

Step 11: Add Modulator for Pitch Variation

1. Right-click → Search "Modulator" → Add Modulator node
2. Connect Random output to Modulator input
3. Select the Modulator node
4. In Details, set:
   • Pitch Min: 0.9
   • Pitch Max: 1.1
   • Volume Min: 0.9
   • Volume Max: 1.0

Step 12: Connect to Output

1. Connect Modulator output to the Output node (speaker icon)
2. The output node should already exist in the graph

Step 13: Test the Sound Cue

1. Click Play Cue button in the toolbar multiple times
2. You should hear different footstep variations each time
3. Pitch should vary slightly for natural sound
4. Save the Sound Cue

Figure: Complete Sound Cue with random selection and pitch/volume modulation.

Part 5: Create Sound Attenuation

Step 14: Create Attenuation Asset

1. Right-click in Audio/SFX → Sounds → Sound Attenuation
2. Name it SA_Footsteps
3. Double-click to open

Step 15: Configure Attenuation

1. In Details, find Attenuation (Volume) section
2. Enable Enable Volume Attenuation (should be on by default)
3. Set Attenuation Function: Natural Sound
4. Set Inner Radius: 100 (full volume within 1 meter)
5. Set Falloff Distance: 2000 (audible up to 20 meters)

Step 16: Configure Spatialization

1. Find Attenuation (Spatialization) section
2. Enable Spatialize
3. Set Spatialization Algorithm: Default (or Binaural for headphones)

Part 6: Test 2D vs 3D Audio

Step 17: Set Up Test Level

1. Open your test level (or create a simple one)
2. Make sure you have a playable character

Step 18: Add 3D Sound Source

1. In the level, create an empty Actor or use an existing mesh
2. Add an Audio Component to it
3. In Audio Component details:
   • Set Sound: SC_Footstep
   • Set Attenuation Settings: SA_Footsteps
   • Enable Auto Activate
   • Enable Is Looping (for testing)

Step 19: Test 3D Spatialization

1. Play the level (PIE)
2. Walk toward the sound source — volume should increase
3. Walk away — volume should decrease
4. Walk around it — sound should pan left/right
5. Move outside the falloff distance — sound should be silent

Step 20: Test 2D Audio

1. Create another Audio Component (or modify existing)
2. Set Sound to your UI click or ambient sound
3. In Details, find Attenuation section
4. Uncheck Override Attenuation or leave Attenuation Settings empty
5. The sound will play as 2D — same volume regardless of position

Troubleshooting

Bonus Challenges

1. Surface-Based Footsteps: Create separate Sound Cues for grass, stone, and wood, then switch based on surface type
2. MetaSound Experiment: Create a simple MetaSound that generates a tone procedurally
3. Reverb Zones: Add Audio Volume actors with different reverb settings for indoor/outdoor areas
4. Volume Options: Create a UI slider that adjusts the SC_Master Sound Class volume
5. Ambient Layers: Create an ambient Sound Cue that mixes wind, birds, and distant sounds

Summary

In this lesson, you've learned the fundamentals of audio in Unreal Engine. Understanding the audio pipeline, import workflows, and the difference between Sound Cues and MetaSounds prepares you to create rich, immersive soundscapes for your games.

Key Concepts

Audio Pipeline: Sound flows from imported Sound Waves through processing (Sound Cues/MetaSounds) to Audio Components, categorized by Sound Classes, mixed through Sound Mixes, and output to speakers. Understanding this flow helps you troubleshoot and optimize.

Supported Formats: Import as WAV for best quality—Unreal compresses during packaging. Use OGG for pre-compressed files. Mono for 3D spatialized sounds, Stereo for music and UI.

Sound Cues: Node-based sound processing for randomization, layering, and simple logic. Use Random nodes for variation, Modulator for pitch/volume randomization. Great for footsteps, gunshots, and varied sound effects.

MetaSounds: Advanced procedural audio system with full DSP capabilities. Use when you need runtime parameter control, synthesis, or complex reactive audio. Steeper learning curve but more powerful.

2D vs 3D Audio: 2D audio plays at constant volume (music, UI). 3D audio is spatialized in the world with distance attenuation and directional panning. Use mono sources for proper 3D spatialization.

Sound Attenuation: Controls how 3D sounds behave over distance. Configure inner radius (full volume zone), falloff distance (audible range), and attenuation function (linear, logarithmic, natural).

Sound Classes: Categorize sounds for separate volume control. Create hierarchy (Master → SFX/Music/Voice). Essential for implementing player volume preferences.

Audio Asset Quick Reference

Sound Cue Common Nodes

Best Practices

• Use mono for 3D sounds: Stereo files cannot be properly spatialized in 3D space
• Import as WAV: Let Unreal handle compression for maximum quality and flexibility
• Stream long audio: Enable streaming for music and long ambient sounds to save memory
• Organize with folders: Separate SFX, Music, Ambient, UI, and Voice audio
• Set up Sound Classes early: Assign all sounds to classes from the start for easy volume control
• Use variation: Random selection and pitch modulation prevent repetitive audio
• Configure attenuation thoughtfully: Match falloff to the sound's real-world behavior
• Test in-game: Audio that sounds good in the editor may need adjustment in actual gameplay

Figure: Audio flows from source files through processing and playback to final mix output.

What's Next?

Now that you understand audio fundamentals, the next lesson covers Playing Sounds. You'll learn how to trigger sounds from Blueprints using Play Sound 2D, Play Sound at Location, and Audio Components. You'll wire up sound effects to gameplay events like collisions, pickups, and player actions.

Knowledge Check