3-D Spatialization and Localization and Simulated Surround Sound with Headphones

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3-D Spatialization and Localizationand Simulated
Surround Sound with Headphones

• Lucas ONeil
• Brendan Cassidy

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Overview

• 3D with headphones
• HRTF Model
• Convolution
• 360 elevation Panning
• Upmixing
• Pro Logic
• Delays
• Filters
• Sub
• Autopanning
• Downmixing with HRTF

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Mathematical HRTF Model

• We tell 3D directionality through 3 cues other
  than just ITD and IID
• Pinna Reflections
• Shoulder and Torso Reflections
• Head Shadow and ITD
• Can model using filters/delays.

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• Shoulder/Torso reflection simulated by echo
• Pinna reflections via a tapped delay line

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• Head shadow diffracts the sound wave.
• Simulated in digital domain by 1st order IIR
  filter
• ITD due to separation obtained by allpass filter
  with group delay

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• Input azimuth and elevation angle.
• Delay by shoulder echo.
• Add delay line due to pinna reflections.
• Filter through Head Shadow and ITD filters.
• spatialization!

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Convolving with HRIR

• HRIR Head Related Impulse Response
• Measured with KEMAR dummy (MIT)
• Convolve audio with impulse response
  corresponding to appropriate angle

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360 Corkscrew Panning

• Demo to shown point source spatialization.
• Pick rotation frequency for azimuth and
  elevation.
• Breaks up signal into blocks and performs HRTF
  with different angles on each block to simulate
  360 rotation around head and elevation from -90
  to 90
• Done with both mathematical model and convolution
  techniques.

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5.1 Surround Sound
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Upmixing to 5.1 Surround

• Investigated Dolby Pro Logic decoder.
• Initially used gains/phase shift matrix to split
  up stereo signal
• Tweaked further adding delays to center and
  surround channels

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• Pro Logic II has 3 modes of operation
• Movie (not used in this project)
• Pro Logic
• Music
• Surround channel uses 7kHz LPF in Pro Logic mode
• Surround channel uses Shelving Filter in music
  mode
• Used 4kz cutoff for shelving.
• Surround channel has 20ms delay in Pro Logic
  mode, but not music mode

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Subwoofer Simulation

• 5 channel surround was losing some low frequency
  due to cross talk corellation and phase
  cancellation in surround channels.
• Solved by cloning low frequencies of signal
  (using 300Hz LPF), then mixing them back in the
  stereo channel after downmixing the 5 channels

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Autopanning

• Pro Logic mode uses autopanning to detect
  directionality and adjust 5 speaker mix.
• Preserves RMS energy in signal.

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Sub-band Autopanning

• Scope of project did not allow for implementation
• Surround upmixer breaks signals into bands and
  pans those bands to the appropriate location
• Can detect different instruments in music (like
  frequency keying in DAW software) and localize
  each instrument.

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Dolby Pro Logic Decoder
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Our Implementation of Upmixer
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Downmixing with HRTF
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• Resultant stereo sound file has convincing
  spatialization effects.
• Pro Logic mode autopanning implemented without
  sub-band separation tends to have vocals that
  jump back and forth across the left and right
  channels.
• Music mode sounded better (for music).

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Questions?