Perception of Sound Positions
In the real world, the perception of a sound's position in space is influenced by several factors. Not all of these factors are acoustical; one of the most important is sight. Clues from the sounds themselves include the following:
- Overall loudness. As a sound source moves away from the listener, its perceived volume decreases at a fixed rate. This phenomenon is known as rolloff.
- Interaural intensity difference. For example, a sound coming from the listener's right sounds louder in the right ear than in the left.
- Interaural time difference. For example, a sound coming from the listener's right arrives at the right ear slightly before it arrives at the left ear. The difference is approximately a millisecond.
- Muffling. The shape and orientation of the ears ensures that sounds coming from behind the listener are slightly muffled compared with sounds coming from the front. In addition, if a sound is coming from the right, the sound reaching the left ear will be muffled by the mass of the listener's head as well as by the orientation of the left ear.
- Effect of the pinnae. The ridges of the earlobes alter the pitch and timing of sounds arriving from different directions, giving subtle clues to the brain about the location of the sound source. The mathematics behind this effect are known as the head-related transfer function (HRTF).
Microsoft DirectSound creates virtual 3-D effects on two speakers or headphones, or on multichannel systems with Microsoft Windows Driver Model (WDM) drivers if the user has chosen a surround sound speaker configuration in Control Panel. For more information, see BufferDescription.