Computers Synthesize Sounds

Computer-generated imagery usually relies on recorded sound to complete the illusion. Recordings can, however, limit the range of sounds you can produce, especially in future virtual reality environments where you can't always know ahead of time what the action will be. Researchers developed computer algorithms to synthesize sound on-the-fly based on simulated physics models. Now they have devised methods for synthesizing more realistic sounds of hard objects colliding and the roar of fire. To synthesize collision sounds, the computer calculates the forces computer-generated objects would exert if they were real, how those forces would make the objects vibrate and how those vibrations transfer to the air to make sound. Previous efforts often assumed that the contacting objects were rigid, but in reality, there is no such thing as a rigid object, researchers say. Objects vibrate when they collide, which can produce further chattering and squeaking sounds.

Resolving all the frictional contact events between rapidly vibrating objects is computationally expensive. To speed things up, their algorithm simulates only the fraction of contacts and vibrations needed to synthesize the sound. Demonstrations include the sound of a ruler overhanging the edge of table and buzzing when plucked, pounding on a table to make dishes clatter and ring and the varied sounds of a Rube Goldberg machine that rolls marbles into a cup that moves a lever that pushes a bunny into a shopping cart that rolls downhill. Fire is animated by mimicking the chemical reactions and fluid-like flow of burning gases. But flame sounds come from things that happen very rapidly in the expanding gases, and computer animators do not need to model those costly details to get good-looking flames. They demonstrated with a fire-breathing dragon statue, a candle in the wind, a torch swinging through the air, a jet of flame injected into a small chamber and a burning brick. The last simulation was run with several variations of the sound-synthesis method, and the results compared with a high-speed video and sound recording of a real burning brick.

More information:

http://www.news.cornell.edu/stories/Aug11/FireContactSound.html