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 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?