Wave Field Synthesis

Transcription

1 Wave Field Synthesis Marije A.J. Baalman Institute for Audio Communication Technische Universität Berlin Wave Field Synthesis 10. Juli 2007 p. 1/26

2 Overview What is wave field synthesis? Possibilities and limitations The WFS system in H0104 WFS software swonder Assignment Wave Field Synthesis 10. Juli 2007 p. 2/26

3 What is Wave Field Synthesis? Huygens principle WFS Wave Field Synthesis 10. Juli 2007 p. 3/26

4 Fachgebiet Audiokommunikation Derivation wave field synthesis y integration line speakers source r0 y 0 r0 z x reference line Wave Field Synthesis 10. Juli 2007 p. 4/26

5 Derivation wave field synthesis Wave field synthesis operator (in the frequency domain): (1) jk Q(x,ω) = S(ω) 2π r0 cos(φ 0 ) e jkr0 r 0 + r 0 r0 x is the speaker coordinate k = ω c, the wave number S(ω) is the audio signal delay factor: r 0 c amplitude factor: 1 2π r0 r 0 +r 0 cos(φ 0 ) 1 r0 filtering factor: jk Wave Field Synthesis 10. Juli 2007 p. 5/26

6 Basic source types Wave Field Synthesis 10. Juli 2007 p. 6/26

7 Possibilities Synthesize sound sources on specific places, even in front of the loudspeakers Moving sound sources Simulate acoustics of a room, by synthesizing reflections No sweet spot, but a large listening area! Wave Field Synthesis 10. Juli 2007 p. 7/26

8 Limitations Frequency limitations High frequencies limited through spatial aliasing: the further apart the speakers, the lower the high frequency limit Low frequencies limited by size of speakers subwoofers! A lot of speakers are needed! Computation: for each speaker a signal needs to be calculated Wave Field Synthesis 10. Juli 2007 p. 8/26

9 Spatial aliasing (2) f c x(1 + sinα pw ) where α pw is the incidence angle with the normal on the speaker array of the plane wave. For frequencies above this aliasing frequency, there will be components present in the wavefield with incidence angles: (3) sinα pw,ηal = 2π x η al + ω c sinα pw ω c Wave Field Synthesis 10. Juli 2007 p. 9/26

10 Spatial aliasing freq: 10 khz, x = 15cm, incidence angle = 90 Wave Field Synthesis 10. Juli 2007 p. 10/26

11 Moving sources Change of location over time change of delay over time interpolation of samples Doppler effect Wave Field Synthesis 10. Juli 2007 p. 11/26

12 Room simulation Simulation of the spatial reflection pattern of a room: Early reflections (up to ca ms) Reverberation (from ca ms) Techniques: Recording a real space using array technology Synthesis by using mirror image sources and reverb via plane waves from different directions Effects: Better localisation of sound sources (perception!) Feeling of envelopment and presence Wave Field Synthesis 10. Juli 2007 p. 12/26

13 WFS in lecture hall H0104 Project part of renovation of the lecture halls, including the renewal of the media facilities Participants: Planning Christoph Moldrzyk Loudspeakers Anselm Görtz, Christoph Moldrzyk Software Marije Baalman control Simon Schampijer render Torben Hohn GUI Eddie Mond score Daniel Plewe cluster / offline render Thilo Koch Wave Field Synthesis 10. Juli 2007 p. 13/26

14 Some numbers 840-channel WFS system 2730 loudspeakers speaker distance 10 cm. ca. 100 meter total wall length ca. 700 seats Wave Field Synthesis 10. Juli 2007 p. 14/26

15 Hardware setup User interface Control PC ETHERNET Mixing desk MADI MADI bridge Microphone Stereo input DVD input ETHERNET cluster Render PC Render PC MADI MADI MADI MADI to ADAT MADI to ADAT ADAT ADAT speaker panel speaker panel speaker panel speaker panel speaker panel speaker panel Wave Field Synthesis 10. Juli 2007 p. 15/26

16 Loudspeaker panel 8 channel ADAT input 3 small speakers per channel (5.5 khz, 10 khz, 17kHz, distance 10cm) per 4 channels 1 larger speaker (<> 200 Hz, distance 40cm) Wave Field Synthesis 10. Juli 2007 p. 16/26

17 Software architecture User interface OSC OSC Score player Control unit OSC OSC OSC OSC Render unit Render unit Offline render unit Offline render unit N N Wave Field Synthesis 10. Juli 2007 p. 17/26

18 Rendering architecture sound input per source direct sound weighted delay lines (twonder) + output per speaker early reflections short convolution (fwonder) reverberation long convolution (fwonder) 8 plane wave delay lines (twonder) Wave Field Synthesis 10. Juli 2007 p. 18/26

19 Control unit The control unit is the communication center for the various components. The control unit reacts on messages from a user interface, parses these and gives subsequent commands to the renderer and offline renderer, and informs the user interface of the current status of the system. This is managed by various streams: render visual score timer Wave Field Synthesis 10. Juli 2007 p. 19/26

20 Current Tools Control unit (cwonder) Render units (twonder and fwonder) LADSPA plugin for single source control LADSPA plugin for source group control SuperCollider class 3D Visualiser (implemented in Fluxus) Wave Field Synthesis 10. Juli 2007 p. 20/26

21 In development User interface (xwonder) Score player VST plugins Wave Field Synthesis 10. Juli 2007 p. 21/26

22 OpenSoundControl Some examples of OSC commands: /WONDER/source/position /WONDER/source/type /WONDER/source/mute /WONDER/scene/select /WONDER/scene/set /WONDER/project/load /WONDER/project/save Wave Field Synthesis 10. Juli 2007 p. 22/26

23 Screenshots Wave Field Synthesis 10. Juli 2007 p. 23/26

24 WFS System in the small studio 24 speakers (FOSTEX personal monitor 6301B) PC with RME Hammerfall soundcard running Linux swonder - software Wave Field Synthesis 10. Juli 2007 p. 24/26

25 Assignment Construct a scene on the WFS system in the small studio, using Ardour and LADSPA plugins, where you show: putting several sources on different positions using movement of some sources adding reflections to specific sources by adding source positions (mirror image sources) and reverb (using one of the LADSPA plugins for reverb) as plane waves Write a short protocol on how you created the audio scene (concept) and a description of the result. Next week: play the scene! Wave Field Synthesis 10. Juli 2007 p. 25/26

26 More information Library of our institute (KW2) Google Wave Field Synthesis Contact: Wave Field Synthesis 10. Juli 2007 p. 26/26