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3-D Spatialization and Localization and Simulated Surround Sound with Headphones Lucas O’Neil Brendan Cassidy Overview 3D with headphones HRTF Model Convolution 360 + elevation Panning Upmixing Pro Logic Delays Filters Sub Autopanning Downmixing with HRTF Mathematical HRTF Model

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3 d spatialization and localization and simulated surround sound with headphones

3-D Spatialization and Localizationand Simulated Surround Sound with Headphones

Lucas O’Neil

Brendan Cassidy

overview
Overview
  • 3D with headphones
    • HRTF Model
    • Convolution
    • 360 + elevation Panning
  • Upmixing
    • Pro Logic
    • Delays
    • Filters
    • Sub
    • Autopanning
  • Downmixing with HRTF
mathematical hrtf model
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.
slide4
Shoulder/Torso reflection simulated by echo:
  • Pinna reflections via a tapped delay line
slide5
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:
slide6
Input azimuth and elevation angle.
  • Delay by shoulder echo.
  • Add delay line due to pinna reflections.
  • Filter through Head Shadow and ITD filters.
  • spatialization~!
convolving with hrir
Convolving with HRIR
  • HRIR = Head Related Impulse Response
  • Measured with KEMAR dummy (MIT)
  • Convolve audio with impulse response corresponding to appropriate angle
360 corkscrew panning
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.
upmixing to 5 1 surround
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
slide12
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
subwoofer simulation
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
autopanning
Autopanning
  • Pro Logic mode uses autopanning to detect directionality and adjust 5 speaker mix.
  • Preserves RMS energy in signal.
sub band autopanning
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.
slide19
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).