Virtualized Surround Sound over Headphones

Conventional headphone playback does not provide the spatial cues that a listener would normally experience with playback over loudspeakers. The result is an unnaturally wide stereo image that forms a straight line between the user's ears. Left and right sounds appear to occur directly beside the listener, whereas center sounds appear to be within the listener's head.

Virtualized surround sound allows users who are wearing headphones to distinguish sound from front to back as well as from side to side. This is done by transmitting spatial cues that help the brain localize the sounds and integrate them into a sound field. This has the effect of making the sound feel like it transcends the headphones, creating an "outside-the-head" listening experience.

This effect is achieved by using a technology called Head Related Transfer Functions (HRTF). HRTF generates acoustic cues that are based on the shape of the human head. These cues not only help listeners to locate the direction and source of sound but it also enhances the type of acoustic environment that is surrounding the listener.

HRTF are measurable characteristics that account for the near-ear response, far-ear response, and interaural delay (the delay between the two ears in perceiving a sound). These characteristics are synthesized with digital signal processing and delivered to headphones. The brain then interprets the three-dimensional spatial cues to re-create an exceptional listening experience.