A brief discussion on auditory dimensions and surround sound

                 A brief discussion on auditory dimensions and surround sound

We live in a three-dimensional world, that is, a three-dimensional world consisting of three dimensions: width, height, and depth. We feel that everything in this world is three-dimensional. We mainly identify the orientation and distance of objects through vision and sound. . The human ear can distinguish sounds from all directions within a spherical range with the head as the origin.

How the human ear identifies the direction of sound

How do ordinary people, who only have two ears, discern spatial information with three dimensions? ——Refer to the description of the binaural effect: People rely on the volume difference, time difference and timbre difference between the two ears to determine the direction of the sound. When the sound intensity is different, you can feel the distance between the sound source and the listener.

1. The volume difference between the sound reaching the two ears

When a sound comes from our left side, the sound heard by the left ear is naturally louder, and we will feel that the sound is located to the left. This is how the Pan knob on the mixer works. When we turn the Pan knob, we actually change the volume ratio of the left and right channels. The volume difference here also includes the ratio of direct sound and reflected sound. Imagine that we are sitting in front of a pair of speakers in the room. When we turn our head 90 degrees to the right, the left ear can hear the direct sound of the speakers, and the right ear can hear the direct sound of the speakers. My ears can hardly hear the direct sound anymore. What my right ear hears is the sound from the speaker that has been reflected from the walls of the room. The ratio of direct sound and reflected sound received by the ear is also an important reference for the human ear to distinguish the direction of sound.

As shown in the picture: the sound comes from the right side, the right ear can hear the direct sound, and the left ear can only hear the reflected sound and diffraction sound from the environment because it is blocked by the head. Of course, there is a clear difference in the volume between the two. The direct sound will definitely be louder. The direction of the sound can be easily distinguished by the ratio of the volume reaching the left and right ears.

2. The time difference between the sound reaching the two ears

Similarly, when a sound is emitted from one side, the time it takes to reach the two ears is different. Although this time difference is very small, the nervous system can still capture it and use it to analyze the direction of the sound.

As shown in the figure: the sound is emitted from the front right, blue indicates the direct sound path to the right ear, and orange indicates the path to the left ear. It is obvious that the orange path is longer than the blue path. At the same speed of sound, longer propagation distance is required. longer. Obviously, the right ear hears the sound before the left ear.

3. Poor timbre

Our heads and bodies will block the sound to a certain extent, and these blocks will cause the frequency of the sound to change. Therefore, when a sound is in the direct sound range that can be heard by the ears, we will feel that the sound is very clear and direct, but when the sound comes from the top of the head, the soles of the feet, or the rear, we will feel that the sound is muffled. The human body and auricle partially block the sound, resulting in a change in timbre. This change in timbre is also a reference for the human ear to analyze the direction of the sound.

When the sound source comes from the right, the right ear can hear the direct sound, but the left ear cannot hear the direct sound due to the obstruction of the head. The obstruction of the head and the reflection of the environment will definitely cause some frequencies of the sound to be attenuated. The timbres heard by the ears are different.

When sound comes from directly in front and directly behind, the volume difference and time difference received by the two ears are almost the same. How do we distinguish whether the sound is from the front or the rear? At this time the shape of the ears plays a key role. When the sound comes from the rear, it is partially blocked by the ears, and the timbre of the sound is different from the sound coming from the front. We can distinguish the front and rear directions of the sound through the timbre difference.

Since our auricles are facing forward, when we receive sounds from directly in front and directly behind, due to the interference and obstruction of the ear shape, the timbre of the sounds directly in front and directly behind will be different. The difference in timbre is when the volume is different, When the time difference is close, it is an important basis for distinguishing the direction.

In addition, head rotation and visual aids are also ways to identify the location of sounds. When we cannot clearly distinguish the direction of the sound, we can easily identify the location of the sound by turning our head to change the direction of the sound to the ears. With the aid of vision, we can easily identify the location of the sound.

When we are in a place where it is difficult to distinguish the position of a sound, we turn our head to cause the two ears to deviate from the position of the sound. At this time, the originally very similar parameters begin to be clearly distinguished, and it is easy for us to distinguish the position of the sound.

After talking about how to identify the direction of sound, let’s talk about it again

Dimensions of sound

The listening devices we have access to today are probably headphones and speakers. Commonly used headphones are in-ear headphones and headphones. Almost all headphones have speakers that directly reach the ear canal, so usually headphones only have direct sound; in terms of quantity, speakers Common ones are 2.1, 5.1, 7.1, 9.1, 7.1.4, 9.1.4, etc. Since the speakers are played in a real room, the sound emitted from the speakers will be reflected multiple times by the table and walls of the room to form reverberation. We live in a world full of reverberation, so speakers give us a more realistic hearing experience than headphones.

Room reverberation indication: When we make sound in the room, not only the direct sound reaches other people's ears, but also the reverberation sound formed by the near reflection sound and far reflection sound from the wall, ceiling, and tabletop. Therefore, the big difference between the sound of speakers and headphones is that the sound coming out of speakers has room reverberation, while headphones only have direct sound.

From the perspective of the sound dimension, the sound brought by headphones is one-dimensional, and the sound position can only move along the left, middle and right lines connecting the two ears, which is the "mid-head effect". So when we put on headphones to listen to music, we will feel that the sound is in the left ear, or the right ear, or the middle of the connection between the left and right ears is inside the head, just like a band playing inside the head. This feeling is quite opposite. Human beings. Therefore, headphones cannot give us a correct sound field, which is one of the biggest shortcomings of headphones compared to speakers.

When we listen to music with headphones, the sound from the headphones is one-dimensional because the sound field has only one line without any depth.

The speakers from 2.1, 5.1, 7.1 to 9.1 are all two-dimensional, that is, a fan-shaped or circular plane surrounding the listener. 2.1 is the most basic configuration. 2.1 refers to left and right channel full-range speakers plus a subwoofer. 2.1 configurations are common in multimedia desktop speakers, monitor speakers, etc. The maximum sound phase range provided by 2.1 is limited to a span of 120° from the front left to the front right. According to the way the human ear locates sound, when listening to 2.1 speakers, the sound information received from the left and right sides is highly similar and sounds very similar to the sound coming from the front, so the brain will default to the sound coming from the front instead of the left and right. both sides. Panning width and depth are the most fundamental differences between speakers and headphones for listening to music.

The sound of 2.1 channel is usually in the range of 60-120° from left to right. When using 2.1 speakers, a virtual sound phase will be synthesized directly in front, and it feels like the sound is coming from the screen directly in front.

5.1-channel is common in home theaters. Compared with 2.1-channel, it adds three rear left and right surround speakers and a center speaker. In this way, the range of the sound phase is a circle surrounding the listener. The sound can be perceived from 60° to the left and right in front and 120° to the left and right in the rear. At this time, the listener will have the feeling of being surrounded by the sound, so starting from the 5.1 channel Enter the world of surround sound.

The 7.1 channel adds speakers on the left and right sides based on the 5.1 channel. In comparison, the positioning of the rear surround speakers will be clearer, while the 9.1 channel adds a set of front left and right speakers on the basis of the 7.1 channel. speakers, making the coverage angle of the speakers more complete. But even if it goes up to 9.1 channels, the sound is still a circular plane surrounding the listener, because all the speakers are at the same plane height and are still two-dimensional.

With a common 7.1-channel home theater configuration, you can experience a theater-like surround sound experience at home. The sound phase range is a flat circle surrounding the listener.

Panoramic sound is usually a 9.1.4 configuration, that is, 9 flat surround speakers, a subwoofer, and 4 sky channel speakers are hung in a group on the left and right sides above the front and back of the audience. At this time, we You can feel the sound surrounding you from the front, back, left, right and above, which can be said to be immersive. However, panoramic sound has not yet been popularized for civilian use. Not only is the construction cost high, but also the sound sources are very scarce, so usually we can only go to theaters to experience panoramic sound.

Cinema panoramic sound is usually equipped with a very large number of speakers for surround. In addition to a circle of surround speakers, cinema panoramic sound is also equipped with a considerable number of sky channels. Multiple speakers form a matrix network, allowing sound to be positioned randomly in the network. In this way, the sound can really come from all directions, which is true panoramic sound.

In addition to speaker configuration, cinema panoramic sound uses panoramic sound production software to position the sound during the sound source production stage. Based on a certain number of speaker matrices and the panoramic sound algorithm, the sound source can be positioned anywhere in the theater.

Although the surround sound system is very enjoyable to use, especially when watching movies and playing games at home, the high price of the surround sound system, which often costs tens of thousands, is prohibitive, and the surround sound system has relatively high requirements for the construction environment, so The current penetration rate is not very high.