Transcript 3-D Spatialization and Localization and Simulated Surround Sound with Headphones Lucas O’Neil

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
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Pro Logic
Delays
Filters
Sub
Autopanning
• Downmixing with HRTF
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.
• Shoulder/Torso reflection simulated by echo:
• Pinna reflections via a tapped delay line
• 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:
• 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
• HRIR = Head Related
Impulse Response
• Measured with
KEMAR dummy (MIT)
• Convolve audio with
impulse response
corresponding to
appropriate angle
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.
5.1 Surround Sound
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
• 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
• 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
• Pro Logic mode uses autopanning to
detect directionality and adjust 5 speaker
mix.
• Preserves RMS energy in signal.
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.
Dolby Pro Logic Decoder
Our Implementation of Upmixer
Downmixing with HRTF
• 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).
Questions?