人机交互技术4—输出设备 Sound and Haptics.ppt

Output Devices(Sound and Haptics) Topics 3D sound Haptic feedback Tactile feedback devices (feeling the touch sensation) Force feedback (feeling the force and torque) * 1. 3D Sound The difference between stereo sound and 3D sound is that in 3D sound, the sound changes according to the location and orientation of the user’s head. Human Auditory System Sound waves are reflected by the pinna, which amplifies some frequencies and attenuates others. These changes provide added info. for the brain to determine the direction of sound. The ear canal amplifies sounds between 3-12kHz. The middle ear consists of delicate bones that magnifies the sound pressure from the eardrum. The sound pressure will then be converted into brain signals by the inner ears. 1.1 Azimuth（方位角） Cues The difference in the arrival time of the sound at the two ears is called the ITD, which is computed as a(θ+sinθ)/c, where c is the velocity of sound. Since sound has a fixed propagation velocity in air, it will reach the ear that is closer to the source first. Interaural Time Difference (ITD) As illustrated in the figure, the sound wave reaches the right ear last, since it has to travel an extra distance of a(θ+sinθ), where a is the radius of the head. Interaural Intensity Difference (IID) A second cue used by the brain to estimate the source orientation is the intensity of sound reaching the ears. The closer ear hears a sound with higher intensity than that of the distant ear. This phenomenon, called the head-shadow effect, is detectable for sounds with high frequencies. 2. Haptic Feedback Haptic interfaces convey important sensorial information to help users achieve tactile recognition of virtual objects. When added to the visual and 3D audio feedbacks, haptic feedback may greatly improve simulation realism. Touch feedback conveys real-time information on contact surface geometry, roughness and temperature. Force feedback provides real-time information on virtual object surface propertie