In the realization of surround Audio, whether it is Dolby AC3 or DTS, there is a feature that multiple speakers are required for playback, but due to price and space reasons, some users, such as multimedia computer users, do not enough speakers. At this time, a technology is needed that can process multi-channel signals and play them back in two parallel speakers, and can make people feel the effect of surround Audio. This is the virtual surround Audio technology. The English of virtual surround Audio is Virtual Surround, also called Simulated Surround, people call this technology non-standard surround Audio technology. The non-standard surround Audio system is based on the two-channel stereo, without adding channels and speakers, and broadcasts the Audio field signal through the circuit processing, so that the listener feels that the Audio comes from multiple directions, producing a simulated stereo field. The value of virtual surround Audio The value of virtual surround technology lies in the use of two speakers to simulate the effect of surround Audio. Although it cannot be compared with a real home theater, the effect is ok in the best listening position. The Audio position requirements are high, so it is a good choice to apply this virtual surround technology to headphones. In recent years, people have begun to study the use of the fewest channels and the fewest speakers to create a three-dimensional Audio with a three-dimensional sense. This Audio effect is not as realistic as the mature surround Audio technology such as DOLBY. But because of its low price, this technology is more and more widely used in power amplifier, TV, car audio and AV multimedia. People call this technology non-standard surround Audio technology. The non-standard surround Audio system is based on the two-channel stereo, without adding channels and speakers, and broadcasts the Audio field signal through the circuit processing, so that the listener feels that the Audio comes from multiple directions, producing a simulated stereo field. Virtual Surround Audio Principle The key to the realization of virtual Dolby surround Audio is the virtualized processing of Audio. The surround channel is specially processed according to the principles of human physiological acoustics and psychoacoustics, so as to create a phantom feeling that the surround Audio source comes from the rear or side of the listener. Several effects of the principle of human hearing are applied. Binaural effect. British physicist Rayleigh found through experiments in 1896 that the two ears of a human have a time difference (0.44-0. 5 microseconds), Audio intensity difference and phase difference, and the hearing sensitivity of the human ear can accurately judge the direction of the Audio and determine the position of the Audio source according to these small differences, but it can only be limited to determine the Audio source in the horizontal direction in front, not Solve the localization of 3D empty Audio source. Auricle effect. The human auricle plays an important role in the reflection of Audio waves and the orientation of spatial Audio sources. With this effect, the three-dimensional position of the Audio source can be determined. The frequency filtering effect of the human ear. The Audio localization mechanism of the human ear is related to the Audio frequency. The bass of 20-200 Hz is located by the phase difference, the midrange of 300-4000 Hz is located by the Audio intensity difference, and the treble is located by the time difference. According to this principle, the differences in language and musical tones in the playback Audio can be analyzed, and the surround feeling can be increased through different processing. Head related transfer function. The human auditory system produces different frequency spectra for Audios in different directions, and this spectral characteristic can be described by the head-related transfer function (HRT). To sum up, the spatial positioning of the human ear includes three directions: horizontal, vertical, and front and rear. Horizontal positioning mainly relies on both ears, vertical positioning mainly depends on the ear shell, and front and rear positioning and the perception of the surround Audio field rely on the HRTF function. Based on these effects, virtual Dolby surround Audio artificially creates the same Audio wave state as the actual Audio source at the human ear, so that the human brain produces a corresponding Audio image in the corresponding spatial orientation.