A Toolkit for Customizing the ambix Ambisonics-to- Binaural Renderer

Transcription

1 A Toolkit for Customizing the ambix Ambisonics-to- Binaural Renderer 143rd AES Convention Engineering Brief 403 Session EB06 - Spatial Audio October 21st, 2017 Joseph G. Tylka (presenter) and Edgar Y. Choueiri 3D Audio and Applied Acoustics (3D3A) Laboratory Princeton University 1

2 Ambisonics-to-Binaural Rendering SoundField Microphone HOA Signals Convolve Render as discrete sources Binaural signals HRTFs mh acoustics Eigenmike Sennheiser AMBEO VR Mic Xie (2013), Head-Related Transfer Function and Virtual Auditory Display, Fig

3 Outline Existing tools Structure of binaural rendering configuration The SOFA/AmbiX Binaural Rendering (SABRE) Toolkit Decoding ambisonics HRTF processing Using the toolkit Summary 3

4 Existing Tools Tool Author Platform Maximum Order Ambi Noise Head Makers Custom HRTF Support Free VST 1 Harpex-X Harpex Ltd. VST 1 O3A Decoding VST Blue Ripple Sound SPAT IRCAM JSAmbisonics Library ambix Plug-ins VST 3 Max, C++ Library No limit A. Politis and D. Poirier-Quinot JS Library No limit M. Kronlachner VST

5 Binaural Rendering Configuration Renders HOA to discrete speakers signals Decoder Matrix x 1 (t) x 2 (t). x Q (t) Generally frequency independent Requires a known speaker grid Various decoder types [4,5,6] = D a 0 (t) a 1 (t). a N 1 (t) HRTFs Spatialize discrete signals to binaural Stored as impulse responses with corresponding measurement grid Various storage formats; standardized one is SOFA [2] May require interpolation to decoder s speaker grid May require equalization for playback 5

6 The SOFA/AmbiX Binaural Rendering (SABRE) Toolkit 6

7 Toolkit Architecture EQ Type SOFA HRTFs Design EQ Filters Interpolation Settings Interpolate HRTFs Equalize HRTFs Speaker Grid Decoder Type Load/Design Decoder Matrix ambix Binaural Decoder 7

8 Decoding Ambisonics 8

9 Decoder Matrix Load an existing decoder Built-in ambix presets Ambisonics Decoder Toolbox (ADT) [4] Design basic decoder Pseudoinverse [5] D = Pseudoinverse decoder Y 0 (ˆv 1 ) Y 0 (ˆv 2 ) Y 0 (ˆv Q ) Y 1 (ˆv 1 ) Y 1 (ˆv 2 ) Y 1 (ˆv Q ) Y N 1 (ˆv 1 ) Y N 1 (ˆv 2 ) Y N 1 (ˆv Q ) Compact decoder + Quadrature [6] Compact decoder Pre-multiply HRTFs with decoder matrix [ ] h L,R 1 (t) h L,R 2 (t) h L,R Q (t) D }{{} h L,R Effective HRTFs = h L,R I (N N) }{{} D Effective decoder matrix 9

10 HRTF Processing 10

11 HRTF Interpolation Nearest neighbor Time domain: Time-align onsets Time domain interpolation Average responses & delays Reintroduce average delay Alternatively, frequency domain Weighting schemes: Linear, natural neighbor, spherical harmonic Interpolation threshold: Nearest neighbor if a close enough measurement exists remove delay interpolate introduce delay Otherwise, use specified method 11

12 HRTF Equalization Regularization parameter Equalization type: β None, frontal (free-field), diffuse, horizontal β 1 Regularized inverse filter β 0 f Z(f) = H (f) H (f)h(f)+β(f) [9, Eq. (4)] f L1 f L0 f H0 f H1 β 0 = 10 4, f L0 = 50 Hz, f H0 = 21 khz, β 1 = 10 2, f L1 = 20 Hz, f H1 = 22 khz. 12

13 Using the Toolkit 13

14 Running in MATLAB MATLAB code from examples.m distributed with the toolkit 1. Initialize the toolkit 2. Specify ambisonics order 3. Specify SOFA file and location 4. Specify output ambix filename 5. Generate the renderer! Can also specify optional settings see user manual for details. 14

15 The ambix Binaural Plug-in Click open to select binaural decoder 15

16 Summary Presented a MATLAB toolkit for customizing the ambix binaural decoder Converts any SOFA-formatted HRTFs into ambix rendering configuration Implemented basic ambisonic decoder functionality; compatible with established ambisonic decoder toolbox Implemented several methods of HRTF interpolation and equalization Source code is freely-available on GitHub: Acknowledgements Uses ambix plug-ins: Requires SOFA API: 16

17 References [1] Kronlachner, M., Ambisonics plug-in suite for production and performance usage, in Linux Audio Conference, [2] AES , AES : AES standard for file exchange - Spatial acoustic data file format, [3] Nachbar, C., Zotter, F., Deleflie, E., and Sontacchi, A., ambix - A Suggested Ambisonics Format, in Proceedings of the 3rd Ambisonics Symposium, [4] Heller, A. J., Benjamin, E. M., and Lee, R., A Toolkit for the Design of Ambisonic Decoders, in Linux Audio Conference, [5] Heller, A., Lee, R., and Benjamin, E., Is My Decoder Ambisonic? in Audio Engineering Society Convention 125, [6] Duraiswami, R., Zotkin, D. N., Li, Z., Grassi, E., Gumerov, N. A., and Davis, L. S., High Order Spatial Audio Capture and Its Binaural Head-Tracked Playback Over Headphones with HRTF Cues, in Audio Engineering Society Convention 119, [7] Rafaely, B. and Avni, A., Interaural cross correlation in a sound field represented by spherical harmonics, The Journal of the Acoustical Society of America, 127(2), pp , [8] Schärer, Z. and Lindau, A., Evaluation of Equalization Methods for Binaural Signals, in Audio Engineering Society Convention 126, [9] Farina, A., Advancements in Impulse Response Measurements by Sine Sweeps, in Audio Engineering Society Convention 122,