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Home / News > Ears for the principle of sound recognition


Ears for the principle of sound recognition

It is often said beats earphones that people hear the sound, can identify the voice from which direction to spread over, and the sound spread in different environments and not the same, this is the role of the direction of the sound of the human ear The

Sound source orientation, is the auditory organ to the sound of the pitch, sound intensity, sound, sound sense of feeling another sense of the elements, it involves complex physiological psychology problems. At the same time, the sound source orientation is also the theoretical basis of stereo technology.

First, the time difference, phase difference and sound level difference, sound color difference

Binaural effect to locate the principle of time difference, phase difference, sound level difference, sound color difference.

(A) time difference and phase difference

Time difference mainly refers to the sound just arrived in the ears of the moment differences. The velocity of the sound waves propagating at room temperature is 344m / s. When the sound source deviates from the front axis of the listener, the distance between the ear A and the ear B is the difference between the sound source and the ear The time difference between.

Time difference as the sound source positioning mechanism, the positive and both sides of the sound source positioning accuracy is high, from the back of the sound source positioning error is greater. The reason is not yet clear. May be because the sound from the back side, because the left ear or right ear ear mask effect, making the sound due to diffraction and time difference has changed.

Because the human ear is adaptive to the sound, when the sound reaches the basement membrane of the moment, hair cells are excited and sensitive. When the sound continues to stimulate, hair cell response is relatively slow. So the sound and transient sound of the sound source positioning accuracy is higher.

A rapid flow of sound, will attract the attention of the hearing. Therefore, the direction of the ever-changing voice, the ear of its position to identify the smaller error. This is the reason for the acoustic shift in modern stereo programs.

A continuous sound, although there is a time difference between reaching the ears, but because the followers of the same ear cover the front of the sound, so that the time difference becomes not obvious.

The high frequency sound is consistent with the low frequency sound propagation velocity, so the time difference is independent of the frequency of the same sound source. But the phase difference is related to the frequency of the same source. When a sound reaches the ears, there is a time difference between the ears and cheap beats the phase difference. In a certain frequency range, the phase difference is one of the information of the source orientation.

The phase difference localization mechanism is more effective when the frequency is lower. For example, the wavelength of the 20 Hz sound at room temperature is 17 m, and the 200 Hz is 1.7 m, and the phase difference formed by the time difference can be sensed. And when the sound source is in the high frequency region, for example, 10 pulses of wavelength 85 px, 20 kHz is 42.5 px, the time difference caused by the phase difference even more than 360 锟斤拷, equal to the beginning of another wavelength. The phase difference at this time has no effect as the positioning information, since it has been impossible to distinguish the phase from lag or advance. Thus the high frequency sound belongs to the "chaotic phase difference" information.

(B) sound level difference and sound color difference

Sound level refers to the sound waves reach the ears of different sound intensity. The main reason for the formation of sound level difference is the shielding effect. If the sound waves in the forward direction are obstructed by a geometric size equal to or greater than the acoustic wavelength, a shadowing effect may occur. The principle is: high frequency sound in the face of obstacles encountered in the transmission, because they can not cross the obstacles, behind the obstacles in the formation of sound shadow area; low frequency sound waves longer than the obstacles in the obstacles behind the formation of acoustic diffraction area. The sound of the sound level plays an important role in the high frequency sound, because the high frequency sound waves can not bypass the head of the listener, so the sound in the shadow area of ??the ear than to hear the direct sound of the ear, sound intensity level differences. The higher the frequency, the sound source deviates from the positive axis, the greater the sound level difference.

From the perspective of diffraction effects, low-frequency sound of course, will form a sound level difference. But because the head diameter of 500px or so, low-frequency sound diffraction occurs, the distance is limited, due to diffraction and loss of energy is very small, and thus deviate from the middle axis of the low-frequency sound, to reach the ears of the sound level difference near zero Sound source positioning effect is Beats Headphones Cheap not obvious.

Shading effect on the sound level difference at the same time, it must also play a role in the sound color. We know that the main component of the composition of the tone is the basis of the sound and the top of the harmonic components. For example, a fundamental wave source with a fundamental frequency of 200 Hz and an incident angle of 45 锟斤拷, then its fundamental and low harmonics encounter diffraction effects after head obstruction, and the higher harmonics are head Department of shading and the emergence of high frequency sound shadow area. At this time, the sound reaching the side of the beats earbuds ear is the direct sound (the original sound), and the sound of the other side of the ear changes the sound due to the high frequency loss. The cerebral cortex is based on the tone difference of the ears to identify the sound source orientation. It can be seen that the sound difference is another reflection of the high frequency signal sound level difference.

It should be noted that the formation of the sound color is mainly those of the fundamental frequency of more than 60Hz complex sound source. Because the higher harmonics of the harmonics below 60Hz, the obstacle that encounters the head size (about 500px in diameter) does not produce a shading effect. For example, the fundamental frequency is 30Hz sound, the 16th harmonic is 480Hz, the wavelength is 0.716m, the wavelength is much larger than the head diameter, between the ears will not form a significant sound color difference, its 17,18,19 harmonic , The intensity is very weak, the tone is not meaningful. Therefore, the following 60Hz sound than the IF, high-frequency sound of the sound source azimuth accuracy is lower.

From the difference in intensity and the effect of tone on the binaural effect, it is conceivable that the pure tone is more difficult to locate than the composite tone because the pure tone is a sine wave (a single wave) and can not be constructed.

(C) the sense of sound depth

Sound source depth sense is the distance between the listening person and the sound source, so the sound source depth sense, also known as the sound source distance positioning.

The sense of sound depth is often associated with a digital pattern. When we hear a voice, we feel the general appearance of the sound in addition to the general direction of the sound, but also feel the approximate distance of the sound. To accurately feel the depth of the sound source, you must be familiar with the sound field environment, familiar with the sound source, or directly with the visual to measure the distance between the sound source and their own. This shows that the sense of sound depth is acquired, can be trained.

The depth of positioning is mainly determined by the degree of sound attenuation. Sound waves in the radiation process, the energy dissipation with the propagation distance, first of all higher harmonics in the first amplitude of the first attenuation, the formation of tone changes. The human ear to hear the sound signal, with the brain stored sound signal for comparison, to determine the sound signal sound source depth.

Another way to sense the depth is the sound source comparison method. When there are several different distance from the sound source (array source) exists, the human ear can be close to the point of the source to infer the depth of other sound sources. A plurality of different distances and angles of incidence of the sound source formed by the array of sound source, so that the sound sense of the sense of sound and surrounded by a sense of feeling. And then repeat the sentence: the sound depth of the sense of depth is usually parallel with the visual, by visual experience, relying on visual help to accurately locate.

(D) the combination of time difference and sound level difference

Binaural effects produced by the various differences in the sound source can be a separate sense of the role. When they are combined with each other, it produces a combined effect. If they act on the contrary (under normal circumstances rarely occur), it is not offset each other. Modern stereo technology has proved that the combination of time difference and sound level difference, the sound source azimuth effect is very obvious. Experiments show that under certain conditions, 1ms time difference is equivalent to 5 ~ 12dB sound level difference, the relationship between the interchangeable.

In a hall where the reverberation time exceeds the normal acoustics requirements, the sound of the sound source is reflected and the reverberation sound level is much higher than its direct sound. At this time, the human ear on the sound wave of the first wave of the most sensitive, if the reflection and reverberation for direct sound delay 40 60ms, the human ear may still grasp the sound source orientation. If the delay exceeds this range, the human ear can not tell the original sound to reach the ears of the time difference and sound level difference, it will produce a sense of separation direction, or chaotic sense of direction. This is why a loud echo of the hall, it is often not easy to grasp the sound source position, need to use the eyes of the reason.

Second, the sound source azimuth mechanism

Classical psychoacoustics that people feel mainly rely on the sound of the binaural hearing differences, known as the binaural effect. As the eyes of the scene to create a sense of perspective, three-dimensional sense of the same, through the binaural sound intensity difference between the feeling, you can judge the sound to, produce a sense of stereo. Until modern times, the binaural effect is still the main theoretical basis for the sense of sound source. But in recent years, experts found that single ear loss of hearing people, there are still sound source to determine the ability, so put forward the ear effect of this new theory, so that the sound source azimuth theory is more perfect.

The mechanism of the sound source is very complex. The principle of binaural effect that: because the binaural position in the head two, if the sound source in front of the people in front of the axis, the sound reaches the ears of time, sound intensity and phase is the same; if the sound source deviation Listening to the front of the central axis, the sound reaches the distance between the ears, so the sound will reach the ears of the time difference and phase difference. At the same time, because the side of the ears appear masking effect and thus between the ears sound level difference, sound difference.

Sound source orientation is inherent in the physiological function, but the sound source position of the width, depth and all the digital-related feeling, with a person acquired experience.

Third, the ear effect

As early as a hundred years ago, it was found that monkeys were deaf who still have the ability to identify the sound source, and put forward the idea of ??ear effect, but not for people to pay attention. Until the sixties of this century, when the stereo technology has developed by leaps and bounds, it is recognized that the binaural effect is difficult to explain for some of the sound source orientation, so the ear effect has been re-recognized.

When we were in our childhood, we could have done some interesting tests, such as pulling our ears out into the ears, and we felt that the sound of the outside world suddenly became clear; if the ears were pressed back to the skull, Will find the sound weakened. As mentioned earlier, the ear shell has the function of reflecting and concentrating the sound. At the same time as the ear shell rugged, so the different parts of the ear shell produced by the reflection of sound, than the direct sound later into the ear drum, the formation of a short delay than the direct short-time the amount of repetitive sound, repeat the sound than the amount of direct delay Depending on the angle of incidence.

The ear effect is also effective in judging the sound behind the listener. When a sound comes from behind, the ear shell will block the sound of the high-frequency overtone, so that compared with the front of the sound source, there has been a significant sound color difference; the same time, due to the shadow of the ear shell, from behind the sound will Do not produce reloading. The auditory area of ??the brain compares this information with the signals that were in the past, resulting in the sound source coming from the back.

Four, single ear effect

Monaural effect refers to the binaural effect within the scope of the single ear listening positioning function. There is no doubt that a binaural hearing normal to listen to the ears to identify the sound source position. However, an interesting fact tells us that people are not using the ears to listen to the sound, while the focus on the use of the side of the ear.

For example, when a point source is present at a distance of 35 锟斤拷 from the left side of the listener, the listener sounds the sound and simultaneously detects the general direction of the sound source; if the listener is given the sound source The sound will be turned to the left 35 锟斤拷 to make their own axis at the sound source, so that with the ears (while using the eyes) to identify the exact location of the sound source; if the sound source is still not accurately measured When the attraction is further enhanced, the listener will turn the head to the right with the left ear toward the source and move closer to the sound source until the exact location of the sound source is found. This process, that is, judgment 锟斤拷 correction 锟斤拷 find the three steps, reflecting the auditory positioning of the body coordination mechanism, while the single ear to listen to the importance of positioning in the positioning.

Five, bone conduction mechanism

Binaural effect, monaural effect and ear effect, to provide the main basis for auditory positioning, it seems that the acoustic organism of the auditory organ has been fully answered. However, a detailed thought, found that some of the details of the mechanism of hearing positioning, has not yet been completely reasonable explanation. For example, from the sound source behind the listener, how the human ear is identified. In accordance with the binaural effect and ear effect principle, from the back of the sound recognition, mainly based on the ear shell shading effect, the formation of the sound behind the sound and positive sound difference, and this feeling of sound from the brain hearing on the past experience comparison The Tests show that three months of the baby will be able to determine the sound from behind, the same, an adult can determine a sound from behind and never heard. It can be seen that the positioning of the sound source behind the human ear can not only be attributed to the sound color difference.

Experts believe that there must be an auditory function, to assist the human ear to determine the source from behind the sound source. This function is the mechanism of bone conduction.

On the possibility of bone guide positioning, has always been controversial, the focus of controversy is not the skull can transmit sound waves, but how much external sound waves from the gas guide into bone mass. Some scholars believe that sound waves in the process of communication, from one medium into another medium, the boundaries of the two media will be reflected and incident, according to Newton's second law of motion, can be calculated in the skull of the incident and The sound of reflection. It is calculated that the acoustic intensity of the reflected wave is 99.89% dB and the incident wave is only 0.00003% dB, which indicates that the external acoustic energy is almost completely reflected, so it is determined that the bone conduction localization function is practically absent.

I believe that the key problem is that there is no incident wave, if the recognition of the existence of incidental waves, then the proportion of energy even if the trace, above the critical limit, the human ear can feel.

The hair cells on the basement membrane of the cochlea can be sensed as a slight amount of sound from the bone through the ability to sense the vibration of the displacement of 1/10 ? (1 angstrom equivalent to the diameter of the nitrogen atom).

We know that the ears are on both sides of the head about 114.99999999999999px deep, here and the distance between the various parts of the skull, the appearance of the head of the sound source into the cochlea between the sound waves formed between the bone conduction time difference between the ears There is also a bone conduction time difference. The velocity of the sonic wave in the skull is 3013m / s, the air conduction velocity is 344m / s, the distance between the parts of the head and the ear is about 4.6 ~ 385px. For this reason, there is a time difference between the direct sound of the bone conduction and the air Auditory area according to bone conduction time difference and bone conduction and air conduction between the time difference, quickly determine the sound source orientation.

In theory, the positioning function of bone conduction is omni-directional, therefore, bone conduction mechanism from the front, side, back and head above the sound waves have a role. However, bone conduction function is auxiliary, secondary, is the binaural effect and monaural effect, ear effect of the supplement.