Binaural Audio

3D audio for headphone reproduction.

Principle

Binaural audio recreates the acoustic cues that reach each ear, enabling 3D perception through headphones:

Virtual    HRTF      Left Ear
Source  ──►Filter──►  Signal
   │
   └──►Filter──► Right Ear
                  Signal

HRTF - Head-Related Transfer Function

What is HRTF?

The HRTF describes how sound is filtered by the head, ears, and torso before reaching the eardrums. It varies with:

• Sound source direction (azimuth, elevation)
• Frequency
• Individual morphology

HRTF Components

Cue	Description	Frequency Range
ITD	Time difference between ears	< 1.5 kHz
ILD	Level difference between ears	> 1.5 kHz
Spectral	Pinna filtering	3-10 kHz

Generic vs Individual

• Generic HRTF: Works for most people, easier to implement
• Individual HRTF: Measured or estimated for specific person, more accurate

Recording Techniques

Dummy Head (Binaural Recording)

Recording with a mannequin head containing microphones in ear positions:

• Neumann KU 100
• 3Dio Free Space
• DIY solutions

Captures natural binaural cues of the recording space.

Binaural Synthesis

Creating binaural signals from mono/multichannel sources:

• Apply HRTF filters to each source
• Sum contributions at each ear
• More flexible than recording

Challenges

Front-Back Confusion

Without head movement, front and back can be confused:

• Same ITD and ILD
• Spectral cues help but aren't perfect

Solutions: Head tracking, visual cues, training

Externalization

Sound may seem "inside the head" rather than external:

• Missing room cues
• Generic HRTF mismatch

Solutions: Add room simulation, use individual HRTF

Coloration

Generic HRTFs can color the sound:

• Timbral changes
• Unnatural quality

Solutions: Individual measurement, HRTF personalization

Applications

Virtual Reality

Essential for VR audio:

• Real-time rendering
• Head tracking integration
• 360° soundscapes

Gaming

3D audio in games:

• Enemy positioning
• Environmental awareness
• Immersive experience

Music Production

Monitoring and creation:

• Check spatial mixes on headphones
• Create binaural releases
• Mix verification

Assistive Technology

Spatial audio for accessibility:

• Navigation cues for visually impaired
• Spatial alerts
• Enhanced communication

Software & Plugins

Binaural Plugins

Plugin	Use
dearVR	Music mixing, VR
Waves Nx	Head-tracked monitoring
Sennheiser AMBEO	Mixing, monitoring
Facebook 360	VR content creation

Renderers

Platform	Technology
Apple	Spatial Audio (AirPods)
Sony	360 Reality Audio
Dolby	Atmos for Headphones
Steam	Steam Audio

Head Tracking

Adding head tracking dramatically improves binaural:

• Resolves front-back confusion
• Improves externalization
• More natural experience

Implementation

Head orientation ──► Update HRTF ──► Render audio
      ↑
  IMU sensor

Binaural and Spacelite

Spacelite doesn't directly output binaural, but its outputs can feed binaural renderers:

Spacelite (multichannel) ──► Binaural Renderer ──► Headphones

Use cases:

• Preview multichannel mixes on headphones
• Create binaural versions of spatial content
• Personal monitoring in shared spaces

The HSR spatial distribution can be captured and binauralized for immersive headphone listening.