- Tabletop Ensemble: Touch-Enabled Virtual Percussion Instruments
Zhimin Ren, Ravish Mehra, Jason Coposky, Ming Lin
I3D 2012 (conditionally accepted)
We present an interactive virtual percussion instrument system, Tabletop Ensemble, that can be used by a group of collaborative users simultaneously to emulate playing music in real world while providing them with ?exibility of virtual simulations. An optical multi-touch tabletop serves as the input device. A novel touch handling algorithm for such devices is presented to translate users' interactions into percussive control signals appropriate for music playing. These signals activate the proposed sound simulation system for generating realistic user-controlled musical sounds. A fast physically-based sound synthesis technique, modal synthesis, is adopted to enable users to directly produce rich, varying musical tones, as they would with the real percussion instruments. In addition, we propose a simple coupling scheme for modulating the synthesized sounds by an accurate numerical acoustic simulator to create believable acoustic effects due to cavity in music instruments. This paradigm allows creating new virtual percussion instruments of various materials, shapes, and sizes with little overhead. We believe such an interactive, multi-modal system would offer capabilities for expressive music playing, rapid prototyping of virtual instruments, and active exploration of sound effects determined by various physical parameters in a classroom, museum, or other educational settings. Virtual xylophones and drums with various physics properties are shown in the presented system
Project | Paper(Low res, High res) | Slides | Video | ACM | Bibtex
Tabletop Ensemble - Multiple players performing music using our virtual percussion instruments.
- An Efficient GPU-based Time Domain Solver for the Acoustic Wave Equation
Ravish Mehra, Nikunj Raghuvanshi, Lauri Savioja, Ming Lin, Dinesh Manocha
Applied acoustics
An efficient algorithm for time-domain solution of the acoustic wave equation for the purpose of room acoustics is presented. It is based on adaptive rectangular decomposition of the scene and uses analytical solutions within the partitions that rely on spatially invariant speed of sound. This technique is suitable for auralizations and sound field visualizations, even on coarse meshes approaching the Nyquist limit. It is demonstrated that by carefully mapping all components of the algorithm to match the parallel processing capabilities of graphics processors (GPUs), significant improvement in performance is gained compared to the corresponding CPU-based solver, while maintaining the numerical accuracy. Substantial performance gain over a high-order finite-difference time-domain method is observed. Using this technique, a 1 second long simulation can be performed on scenes of air volume 7500 cu. m till 1650 Hz within 18 minutes compared to the corresponding CPU-based solver that takes around 5 hours and a high-order finite-difference time-domain solver that could take up to three weeks on a desktop computer. To the best of the authors' knowledge, this is the fastest time-domain solver for modeling the room acoustics of large, complex-shaped 3D scenes that generates accurate results for both auralization and visualization.
Project | Paper | Applied acoustics | Bibtex
- Precomputed Wave Simulation for Real-Time Sound Propagation
of Dynamic Sources in Complex Scenes
Nikunj Raghuvanshi, John Snyder, Ravish Mehra, Ming Lin, Naga Govindaraju
ACM SIGGRAPH 2010
We present a method for real-time sound propagation that captures all wave effects, including diffraction and reverberation, for multiple moving sources and a moving listener in a complex, static 3D scene. It performs an offline wave-based numerical simulation over the scene and extracts the perceptually-salient information. To obtain a compact representation, the scene’s acoustic response is broken into two phases: early reflections (ER), and late reverberation (LR), based on a threshold on the temporal density of arriving sound peaks. The LR’s representation is computed and stored once per room in the scene, while the ER’s accounts for more detailed spatial variation by recording multiple simulations over a uniform grid of source locations. ER data is then compactly stored at each source/receiver point pair as a set of peak delays/amplitudes and a residual frequency response sampled in octave bands. We then describe an efficient, real-time technique that uses this precomputed representation to perform binaural sound rendering based on frequency-domain convolutions. We also introduce a new technique to perform artifact-free spatial interpolation of the ER data. Our system demonstrates realistic, wave-based acoustic effects in real time, including diffraction low-passing behind obstructions, “hollow” reverberation in empty rooms, sound diffusion in fullyfurnished rooms, and realistic late reverberation.
Project | Paper(Low res, High res) | Slides | Video | ACM | Bibtex
Train station scene from Valve's SourceTM game engine SDK (http://source.valvesoftware.com).
- Visibility of noisy point cloud data
Ravish Mehra, Pushkar Tripathi, Alla Sheffer, Niloy J. Mitra
Shape Modeling International 2010 (Invited to special issue of Computers & Graphics - Elsevier)
We present a robust algorithm for estimating visibility from a given viewpoint for a point set containing concavities, non-uniformly spaced samples, and possibly corrupted with noise. Instead of performing an explicit surface reconstruction for the points set, visibility is computed based on a construction involving convex hull in a dual space, an idea inspired by the work of Katz et al. We derive theoretical bounds on the behavior of the method in the presence of noise and concavities, and use the derivations to develop a robust visibility estimation algorithm. In addition, computing visibility from a set of adaptively placed viewpoints allows us to generate locally consistent partial reconstructions. Using a graph based approximation algorithm we couple such reconstructions to extract globally consistent reconstructions. We test our method on a variety of 2D and 3D point sets of varying complexity and noise content.
Project | Paper(Low res, High res) | Computer & Graphics - Elsevier | Bibtex
- Abstraction of Man-Made Shapes
Ravish Mehra, Qingnan Zhou, Jeremy Long, Alla Sheffer, Amy Gooch, Niloy J. Mitra
ACM SIGGRAPH Asia 2009Man-made objects are ubiquitous in the real world and in virtual environments. While such objects can be very detailed, capturing every small feature, they are often identified and characterized by a small set of defining curves. Compact, abstracted shape descriptions based on such curves are often visually more appealing than the original models, which can appear to be visually cluttered. We introduce a novel algorithm for abstracting three-dimensional geometric models using characteristic curves or contours as building blocks for the abstraction. Our method robustly handles models with poor connectivity, including the extreme cases of polygon soups, common in models of man-made objects taken from online repositories. In our algorithm, we use a two-step procedure that first approximates the input model using a manifold, closed envelope surface and then extracts from it a hierarchical abstraction curve network along with suitable normal information. The constructed curve networks form a compact, yet powerful, representation for the input shapes, retaining their key shape characteristics while discarding minor details and irregularities.
Project | Paper(Low res, High res) | Slides | Video | ACM | Bibtex
- "Real-Time Rendering of Mesostructures", Ravish Mehra, Subodh Kumar, B.Tech Project Report, Department of Computer Science & Engineering, IIT Delhi, June-2008
