Stereo decryption for home theater

No matter where the audience is in the concert hall, the direct sound is always heard first, and the position of the sonar is judged by the direct sound. One person can distinguish the sound of a certain sound body (sound source) and tone. The sound is strong, but it is difficult to accurately distinguish the specific position of the sound body; when the person listens with two ears, the specific position of the starting sound body can be accurately distinguished, thereby generating a sense of direction of the sound. Since the human ears have a spacing of about t5-18 cm, the sound travels in the air at a speed of 340 cm/. Therefore, the maximum time difference between the direct sound from the same sound source reaching the two ears is Δt=binaural distance/sound speed=0.44-0.5 ms. At the same time, the sound of the direct sound reaching the ears has a certain sound intensity difference and phase difference. Although the difference is very small, the sensitive person's ear can be reflected, and thus the direction of the sound is determined to determine the position of the sound source.

The reflected sound has little effect on the sense of direction of the sound. Physiological acoustic studies have shown that as long as the time difference between the near-resonant sound and the direct sound is less than 50 ms, even if its intensity is many times larger than the direct sound, the direction of the sound is still direct, which is discovered by the German scholar Haas Hass. Therefore, it is called the Haas effect. However, the reflected sound has an important influence on the size of the sound around the auditory judgment. Whether it is the recent near-reverberation or the late reverberation, the reflected sound always reaches the audience from different directions. Although people's hearing can't determine these directions separately, they can get a general impression, so that the audience has the feeling of being surrounded by sound. This is the spatial sense of sound.

The sound localization mechanism of the human ear is related to the frequency of the sound. When the frequency of sound from different positions is low, the corresponding length is longer and can be diffracted from the head, but there is a certain phase difference when reaching the ears. When the frequency of the sound is high, the head is opposite. The blockage of the spread is not negligible, the high-frequency sound is difficult to circulate, and the intensity of the sound reaching the two ears is larger. Therefore, judging the orientation of the low-frequency sound source mainly depends on the time difference and phase difference generated by the sound wave in both ears, and judging the orientation of the high-frequency sound source mainly depends on the intensity difference generated by the sound in both ears. In addition, since the pitch of the human ear is approximately equal to half of the sound wavelength of 800-1 000 H±, it is lower than E100-1. The OO Hz bass signal has a small time difference and phase difference when it reaches both ears, and there is no obvious directional feeling when listening.
The spatial orientation of the human ear includes three directions of horizontal and vertical phases. The horizontal positioning mainly depends on the ears, and the vertical positioning mainly depends on the elliptical ear shell. Since the human ear is one on each side, the horizontal positioning ability of the human ear is far superior to the vertical positioning ability, and of course the front and rear positioning ability is weaker.

According to the above physiological characteristics of the human ear. We can artificially make the sounds reaching the ears have a certain difference of H, phase difference and intensity difference, so that people can form a corresponding sound source illusion in a certain direction. This subjectively perceived sound source illusion is usually It is called a sound image. The effect of modern stereo playback is thus invented. For example, two-channel stereo is based on the difference between the left and right channels to simulate the sound image orientation. The multi-channel surround sound system simulates the orientation of the sound image based on the difference in sound reproduction. And surrounded by feelings. Practice has proved that when the acoustic state produced by the human ear is exactly the same as that of the actual sound source at both ears, the sound image perceived by the human being will be as real and natural as the actual sound source.

The sounds of nature are full of three-dimensionality. In order to truly reflect the characteristics of the original sound field, it is necessary to perfectly reproduce the three-dimensionality of the sound. This is the main reason why modern audio systems use stereo systems. Compared to mono, stereo has four important features:

(1) The sound image has a sense of distribution. In stereo playback, the sound is no longer emitted from a ten-point "point" like a mono, but distributed over a wide range.

(2) High definition. Stereo makes people feel that the sound sources come from different directions, so it sounds like the masking effect between the sound sources is weaker than the mono, which improves the sharpness.

(3) The balance of the voice is good. Due to the distribution characteristics of the stereo reproduction sound image, when the stereo program is produced, it is easier to handle the volume balance of each sound part than the mono sound, and the effect is better, so that the solo, solo, lead vocal, and the like need to be highlighted, and Keep the entire ten program in a more natural balance.

(4) The background noise is low. The monophonic sound signal and the background noise are emitted by the same ten points, and the noise images reproduced in the stereo are distributed to the ten directions. The scattered background noise is naturally lower than the noise of the concentrated Liu.

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