Perception of sound waves. Perception of sound by the human ear. The effect of noise on humans

The human auditory analyzer is a specialized system for the perception of sound vibrations, the formation of auditory sensations and the recognition of sound images. The auxiliary apparatus of the peripheral part of the analyzer is the ear (Figure 15).

There is an external ear, which includes the auricle, external auditory canal and eardrum; the middle ear, consisting of a system of interconnected auditory ossicles - the hammer, incus and stapes, and the inner ear, which includes the cochlea, where the receptors that perceive sound vibrations are located, as well as the vestibule and semicircular canals. The semicircular canals represent the peripheral receptor part of the vestibular analyzer, which will be discussed separately.

The outer ear is designed in such a way that it supplies sound energy to the eardrum. With the help of the auricles, a relatively small concentration of this energy occurs, and the external auditory canal ensures the maintenance of constant temperature and humidity as factors determining the stability of the sound transmitting apparatus.

The eardrum is a thin membrane, about 0.1 millimeters thick, made up of fibers running in different directions. The function of the eardrum is well reflected in its name - it begins to vibrate when sound vibrations of air from the external auditory canal fall on it. At the same time, its structure allows it to transmit almost without distortion all frequencies of the audio range. The auditory ossicle system ensures the transmission of vibrations from the eardrum to the cochlea.

The receptors that provide the perception of sound vibrations are located in the inner ear - in the cochlea (Figure 16). This name is associated with the spiral shape of this formation, consisting of 2.5 turns.

In the middle canal of the cochlea, on the main membrane, there is the organ of Corti (named after the Italian anatomist Corti, 1822-1888). The receptor apparatus of the auditory analyzer is located in this organ (Figure 17).

How does the sensation of sound form? A question that still attracts close attention from researchers. For the first time (1863), a very convincing interpretation of the processes in the inner ear was presented by the German physiologist Hermann Ludwig Ferdinand Helmholtz, who developed the so-called resonance theory. He noticed that the main membrane of the cochlea is formed by fibers running in the transverse direction. The length of such fibers increases towards the apex of the cochlea. This makes clear the analogy between the work of this organ and a harp, in which different tonality is achieved by different lengths of strings. According to Helmholtz, when exposed to sound vibrations, a specific fiber responsible for the perception of a given frequency comes into resonance. A theory very captivating in its simplicity and completeness, but which, alas, had to be abandoned, since it turned out that there were too few strings - fibers - in the main membrane to reproduce all frequencies audible to humans, these strings were stretched too loosely, and besides, they were isolated fluctuations are not possible. These difficulties for the resonance theory turned out to be insurmountable, but they served as an impetus for subsequent research.

According to modern concepts, the transmission and reproduction of sound vibrations are determined by the frequency-resonant properties of all media of the cochlea. With the help of very ingenious experiments, it was discovered that at low oscillation frequencies (100-150 hertz, maybe slightly higher, but not more than 1000 hertz), the wave process covers the entire main membrane, all receptors of the organ of Corti located on this membrane are excited. As the frequency of sound waves increases, only part of the main membrane is involved in the oscillatory process, and the less, the higher the sound. In this case, the resonance maximum shifts towards the base of the cochlea.

However, we have not yet considered the question of how the energy of mechanical vibrations is transformed into the process of nervous excitation. The receptor apparatus of the auditory analyzer is represented by peculiar hair cells, which are typical mechanoreceptors, that is, for which mechanical energy, in this case oscillatory movements, serves as an adequate stimulus. A specific feature of hair cells is the presence of hairs at their top, which are in direct contact with the integumentary membrane. In the organ of Corti, there are one row (3.5 thousand) of internal and 3 rows (12 thousand) of external hair cells, which differ in the level of sensitivity. More energy is required to excite internal cells, and this is one of the mechanisms of the hearing organ to perceive sound stimuli in a wide range of intensities.

When an oscillatory process occurs in the cochlea as a result of movements of the main membrane, and with it the organ of Corti, deformation of the hairs abutting the integumentary membrane occurs. This deformation serves as the starting point in the chain of phenomena leading to the excitation of receptor cells. In a special experiment, it was discovered that if, during the presentation of a sound signal, biocurrents are diverted from the surface of the hair cells and then, amplifying them, brought to a loudspeaker, we will find a fairly accurate reproduction of the sound signal. This reproduction applies to all frequencies, including the human voice. Isn't that a pretty close analogy with a microphone? This is where the name comes from - microphone potential. It has been proven that this bioelectric phenomenon represents a receptor potential. It follows that the hair receptor cell quite accurately (up to a certain intensity limit) through the parameters of the receptor potential reflects the parameters of sound exposure - frequency, amplitude and shape.

During an electrophysiological study of auditory nerve fibers that directly approach the structures of the organ of Corti, nerve impulses are recorded. It is noteworthy that the frequency of such impulses depends on the frequency of the acting sound vibrations. At the same time, up to 1000 hertz, they practically coincide. Although higher frequencies are not recorded in the nerve, a certain quantitative relationship between the frequencies of the sound stimulus and afferent impulses remains.

So, we have become familiar with the properties of the human ear and the mechanisms of functioning of the receptors of the auditory analyzer when exposed to sound vibrations in the air. But transmission is possible not only through the air, but through so-called bone conduction. In the latter case, vibrations (for example, a tuning fork) are transmitted by the bones of the skull and then, bypassing the middle ear, enter directly into the cochlea. Although in this case the method of supplying acoustic energy is different, the mechanism of its interaction with receptor cells remains the same. True, the quantitative relationships are also somewhat different. But in both cases, the excitation that initially arose in the receptor and carries certain information is transmitted along the nervous structures to the higher auditory centers.

How is information about such parameters of sound vibrations as frequency and amplitude encoded? First, about frequency. You obviously paid attention to a peculiar bioelectric phenomenon - the microphonic potential of the cochlea. After all, it essentially indicates that over a significant range, fluctuations in the receptor potential (and they reflect the work of the receptor both in perception and subsequent transmission) almost exactly correspond in frequency to sound vibrations. However, as already noted, in the fibers of the auditory nerve, that is, in those fibers that perceive information from receptors, the frequency of nerve impulses does not exceed 1000 vibrations per second. And this is significantly less than the frequencies of perceived sounds in real conditions. How is this problem solved in the auditory system? Earlier, when we looked at the work of the organ of Corti, we noted that at low frequencies of sound exposure, the entire main membrane vibrates. Consequently, all receptors are excited, and the vibration frequency is transmitted unchanged to the fibers of the auditory nerve. At high frequencies, only part of the main membrane and, consequently, only part of the receptors are involved in the oscillatory process. They transmit excitation to the corresponding part of the nerve fibers, but with a transformation of the rhythm. In this case, a certain part of the fibers corresponds to a certain frequency. This principle is referred to as a spatial coding method. Thus, frequency information is provided by frequency-spatial coding.

However, it is well known that the vast majority of real sounds that we perceive, including speech signals, are not regular sinusoidal oscillations, but processes that have a much more complex form. How, in this case, is the transfer of information ensured? At the beginning of the 19th century, the outstanding French mathematician Jean Baptiste Fourier developed an original mathematical method that allows any periodic function to be represented as the sum of a number of sinusoidal components (Fourier series). It is proven by rigorous mathematical methods that these components have periods equal to T, T/2, T/3 and so on, or, in other words, have frequencies that are multiples of the fundamental frequency. And the German physicist Georg Simon Ohm (whom everyone knows very well from his law in electrical engineering) in 1847 put forward the idea that just such a decomposition occurs in the organ of Corti. This is how another Ohm’s law appeared, which reflects a very important mechanism of sound perception. Thanks to its resonant properties, the main membrane decomposes complex sound into its components, each of which is perceived by the corresponding neuroreceptor apparatus. Thus, the spatial pattern of excitation carries information about the frequency spectrum of a complex sound vibration.

To transmit information about the intensity of sound, that is, the amplitude of vibrations, the auditory analyzer has a mechanism that is also different from the way other afferent systems operate. Most often, information about intensity is transmitted by the frequency of nerve impulses. However, in the auditory system, as follows from the processes just discussed, this method is impossible. It turns out that in this case the principle of spatial coding is used. As already noted, inner hair cells have lower sensitivity than outer hair cells. Thus, different sound intensities correspond to different combinations of excited receptors of these two types, that is, a specific form of spatial pattern of excitation.

In the auditory analyzer, the question of specific detectors (as is well expressed in the visual system) still remains open, however, here too there are mechanisms that make it possible to isolate more and more complex features, which ultimately culminates in the formation of such an excitation pattern that corresponds to a certain subjective image, identified by the corresponding “standard”.

The auditory analyzer perceives air vibrations and transforms the mechanical energy of these vibrations into impulses, which are perceived in the cerebral cortex as sound sensations.

The perceptive part of the auditory analyzer includes the outer, middle and inner ear (Fig. 11.8.). The outer ear is represented by the auricle (sound collector) and the external auditory canal, the length of which is 21-27 mm and the diameter is 6-8 mm. The outer and middle ears are separated by the eardrum - a membrane that is poorly pliable and weakly stretchable.

The middle ear consists of a chain of interconnected bones: the malleus, the incus and the stapes. The handle of the malleus is attached to the tympanic membrane, the base of the stapes is attached to the oval window. This is a kind of amplifier that amplifies vibrations 20 times. The middle ear also has two small muscles that attach to the bones. Contraction of these muscles leads to a decrease in vibrations. The pressure in the middle ear is equalized by the Eustachian tube, which opens into the oral cavity.

The inner ear is connected to the middle ear by the oval window, to which the stapes is attached. In the inner ear there is a receptor apparatus of two analyzers - perceptive and auditory (Fig. 11.9.). The hearing receptor apparatus is represented by the cochlea. The cochlea, 35 mm long and having 2.5 whorls, consists of a bony and membranous part. The bone part is divided by two membranes: the main and vestibular (Reisner) into three canals (upper - vestibular, lower - tympanic, middle - tympanic). The middle part is called the cochlear passage (membranous). At the apex, the upper and lower canals are connected by a helicotrema. The upper and lower canals of the cochlea are filled with perilymph, the middle ones with endolymph. Perilymph resembles plasma in ionic composition, endolymph resembles intracellular fluid (100 times more K ions and 10 times more Na ions).

The main membrane consists of weakly stretched elastic fibers, so it can vibrate. On the main membrane - in the middle channel - there are sound-perceiving receptors - the organ of Corti (4 rows of hair cells - 1 internal (3.5 thousand cells) and 3 external - 25-30 thousand cells). Above is the tectoreal membrane.

Mechanisms of sound vibrations. Sound waves passing through the external auditory canal vibrate the eardrum, which causes the bones and membrane of the oval window to move. The perilymph oscillates and the oscillations fade towards the apex. Vibrations of the perilymph are transmitted to the vestibular membrane, and the latter begins to vibrate the endolymph and the main membrane.

The following is recorded in the cochlea: 1) Total potential (between the organ of Corti and the middle canal - 150 mV). It is not associated with the conduction of sound vibrations. It is due to the level of redox processes. 2) Action potential of the auditory nerve. In physiology, a third - microphone - effect is also known, which consists of the following: if electrodes are inserted into the cochlea and connected to a microphone, having previously amplified it, and various words are pronounced in the cat’s ear, the microphone reproduces the same words. The microphonic effect is generated by the surface of the hair cells, since deformation of the hairs leads to the appearance of a potential difference. However, this effect exceeds the energy of the sound vibrations that caused it. Hence, the microphone potential is a complex transformation of mechanical energy into electrical energy, and is associated with metabolic processes in hair cells. The location of the microphonic potential is the region of the hair roots of the hair cells. Sound vibrations acting on the inner ear impose a microphonic effect on the endocochlear potential.

The total potential differs from the microphone potential in that it reflects not the shape of the sound wave, but its envelope and occurs when high-frequency sounds act on the ear (Fig. 11.10.).

The action potential of the auditory nerve is generated as a result of electrical excitation occurring in the hair cells in the form of a microphone effect and a sum potential.

There are synapses between hair cells and nerve endings, and both chemical and electrical transmission mechanisms take place.

Mechanism for transmitting sound of different frequencies. For a long time, the resonator system dominated in physiology. Helmholtz theory: strings of different lengths are stretched on the main membrane; like a harp, they have different vibration frequencies. When exposed to sound, that part of the membrane that is tuned to resonance at a given frequency begins to vibrate. Vibrations of the tensioned threads irritate the corresponding receptors. However, this theory is criticized because the strings are not tensioned and their vibrations include too many membrane fibers at any given moment.

Deserves attention Bekes theory. There is a resonance phenomenon in the cochlea, however, the resonating substrate is not the fibers of the main membrane, but a column of liquid of a certain length. According to Bekeshe, the higher the frequency of sound, the shorter the length of the oscillating column of liquid. Under the influence of low-frequency sounds, the length of the oscillating column of liquid increases, capturing most of the main membrane, and not individual fibers vibrate, but a significant part of them. Each pitch corresponds to a certain number of receptors.

Currently, the most common theory of perception of sound of different frequencies is “theory of place”, according to which the participation of perceiving cells in the analysis of auditory signals is not excluded. It is assumed that hair cells located in different parts of the main membrane have different lability, which affects sound perception, i.e. we are talking about tuning hair cells to sounds of different frequencies.

Damage in various parts of the main membrane leads to a weakening of electrical phenomena that occur when irritated by sounds of different frequencies.

According to the resonance theory, different parts of the main plate respond by vibrating their fibers to sounds of different pitches. The strength of sound depends on the magnitude of the vibrations of sound waves that are perceived by the eardrum. The stronger the sound, the greater the vibration of the sound waves and, accordingly, the eardrum. The pitch of the sound depends on the frequency of vibration of the sound waves. The frequency of vibrations per unit time will be greater. perceived by the organ of hearing in the form of higher tones (fine, high-pitched sounds of the voice) Lower frequency vibrations of sound waves are perceived by the organ of hearing in the form of low tones (bass, rough sounds and voices).

Perception of pitch, sound intensity, and sound source location begins when sound waves enter the outer ear, where they vibrate the eardrum. Vibrations of the tympanic membrane through the system of auditory ossicles of the middle ear are transmitted to the membrane of the oval window, which causes vibrations of the perilymph of the vestibular (upper) scala. These vibrations are transmitted through the helicotrema to the perilymph of the scala tympani (lower) and reach the round window, displacing its membrane towards the cavity of the middle ear. Vibrations of the perilymph are also transmitted to the endolymph of the membranous (middle) canal, which causes the main membrane, consisting of individual fibers stretched like piano strings, to vibrate. When exposed to sound, the membrane fibers begin to vibrate along with the receptor cells of the organ of Corti located on them. In this case, the hairs of the receptor cells come into contact with the tectorial membrane, and the cilia of the hair cells are deformed. First, a receptor potential appears, and then an action potential (nerve impulse), which is then carried along the auditory nerve and transmitted to other parts of the auditory analyzer.

Modern psychology considers all perception as an action, emphasizing its active nature. This entirely relates to the perception of speech, during which the listener does not simply record and process incoming information, but, showing counter activity, continuously predicts, models it, compares what is actually heard with the model, makes the necessary corrections and, finally, makes a final decision regarding the meaning. contained in the listened part of the message

In order to correctly navigate the world around you, it is important to perceive not only each individual object (table, flower, rainbow), but also the situation, a complex of some objects as a whole (game room, picture, sounding melody) Combine the individual properties of objects and create a holistic image perception helps - the process of a person’s reflection of objects and phenomena of the surrounding world with their direct impact on the senses. The perception of even a simple object is a very complex process that includes the work of sensory (sensitive), motor and speech mechanisms. Perception is based not only on sensations that allow you to feel the world around you every moment, but also on the previous experience of a growing person

A child is not born with a ready ability to perceive the world around him, but learns this. In early preschool age, images of perceived objects are very vague and indistinct. Thus, children of three or four years old do not recognize the teacher dressed in a fox costume at a matinee, although her face is open. If children come across an image of an unfamiliar object, they snatch some detail from the image and, relying on it, comprehend the entire depicted object. For example, when a child sees a computer monitor for the first time, he may perceive it as a TV.

Despite the fact that a child can see and hear sounds from birth, he must be systematically taught to look at, listen to and understand what he perceives. The perception mechanism is ready, but the child is still learning to use it

Auditory responses in infancy reflect the active process of realizing language ability and acquiring auditory experience, rather than passive reactions of the body to sound.

Already during the first month of life, the auditory system improves and the innate adaptability of a person’s hearing to speech perception is revealed. In the first months of life, the child reacts to the mother's voice, distinguishing it from other sounds and unfamiliar voices.

In newborn children, even premature ones, in response to a loud voice or the sound of a rattle, various motor reactions appear: the child closes his eyes, wrinkles his forehead, he has a crying grimace, and his breathing quickens. Sometimes the reactions may be different: the child stretches out his arms, spreads his fingers, opens his mouth, and makes sucking movements. The reaction to a loud sound may also be accompanied by twitching of the eyeballs, constriction, and then dilation of the pupils. In the 2nd week of life, auditory concentration appears - a crying child becomes silent when there is a strong auditory stimulus and listens.

The development of perception in younger preschoolers is directly related to sensory education. Sensory education is aimed at teaching children a more complete, accurate and detailed perception of such properties of objects as color, shape and size. It is the early preschool age that is most favorable for improving the functioning of the child’s sense organs. Well-developed perception is the key to a child’s successful education at school, and is also necessary for many types of professional activities of an adult.

The success of a child’s sensory development largely depends on the competent implementation of special games and activities by adults. Without such activities, children's perceptions remain superficial and fragmentary for a long time, which, in turn, complicates the subsequent development of their thinking, memory, and imagination.

Perception is formed in connection with the development and complication of the activity of analyzers. Faced daily with certain people and with surrounding objects, the child constantly experiences visual, auditory, skin and other irritations. Gradually, the irritations caused by a given object are isolated from all the influences of surrounding objects and phenomena and are associated with each other, which leads to the emergence of a perception of the characteristics of a given object.

Reinforcement is of utmost importance for the formation of perception, as well as other mental processes.

Isolation of a complex of stimuli related to a given object and the formation of connections between them is successful if this object has acquired some important meaning for the child or, due to its unusualness, evokes an indicative-exploratory reflex.

In this case, the correct identification of a complex of stimuli and the formation of appropriate connections is reinforced by the achievement of the necessary result, as a result of which development and improvement of perception occurs

It is typical that the child begins to perceive first what has the greatest vital significance for him, what is associated with the satisfaction of his life needs. Thus, of all the surrounding people and objects, the baby first of all identifies and recognizes the mother who is caring for him. In the future, the circle of perceived objects and phenomena expands more and more.

Preschoolers achieve great success in perceiving words of their native language, as well as in distinguishing simple melodies.

At the same time, the naming of perceived objects and phenomena by an adult, and then by the child himself, attracts past experience associated with this word, which gives the perception a meaningful, conscious character.

Under the conditions of a properly organized pedagogical process, a preschooler gradually learns not to be satisfied with first impressions, but to more carefully and systematically explore, examine, feel the surrounding objects, and listen more carefully to what is said to him. As a result of this, the images of perception of the surrounding reality that appear in his head become more accurate and rich in content.

Simultaneously with visual perception, they also develop other types of perception, among which we should first of all note tactile and auditory ones.

The child is surrounded by many sounds: music, the chirping of birds, the rustling of grass, the sound of the wind, the murmur of water...

By listening to sounds, comparing their sound and trying to repeat them, the child begins not only to hear, but also to distinguish the sounds of his native nature

Hearing plays a leading role in the formation of sound speech. It functions from the first hours of a child’s life. Already from the first month, auditory conditioned reflexes are developed, and from five months this process occurs quite quickly. The baby begins to distinguish the mother's voice, music, etc. Without reinforcement, these reflexes soon fade away. This early involvement of the cortex in hearing development ensures the early development of auditory speech. But although hearing in its development is ahead of the development of movements of the speech organs, at first it is not sufficiently developed, which causes a number of speech imperfections.

The sounds and words of others are perceived undifferentiated (the difference between them is not realized), i.e. unclear, distorted. Therefore, children mix one sound with another and poorly understand speech.

During preschool age, under the influence of appropriate educational work, the role of sound signals in the organization of children's perception increases.

It should be noted that work aimed at developing auditory perception is very important in the overall development of the child’s psyche

The development of auditory perception is of great importance for preparing a preschooler for entering school.

Psychoacoustics, a field of science bordering between physics and psychology, studies data on a person’s auditory sensation when a physical stimulus—sound—is applied to the ear. A large amount of data has been accumulated on human reactions to auditory stimuli. Without this data, it is difficult to obtain a correct understanding of the operation of audio transmission systems. Let's consider the most important features of human perception of sound.
A person feels changes in sound pressure occurring at a frequency of 20-20,000 Hz. Sounds with frequencies below 40 Hz are relatively rare in music and do not exist in spoken language. At very high frequencies, the musical perception disappears and a certain vague sound sensation appears, depending on the individuality of the listener and his age. With age, a person's hearing sensitivity decreases, primarily in the upper frequencies of the sound range.
But it would be wrong to conclude on this basis that the transmission of a wide frequency band by a sound-reproducing installation is unimportant for older people. Experiments have shown that people, even if they can barely perceive signals above 12 kHz, very easily recognize the lack of high frequencies in a musical transmission.

Frequency characteristics of auditory sensations

The range of sounds audible to humans in the range of 20-20,000 Hz is limited in intensity by thresholds: below - audibility and above - pain.
The hearing threshold is estimated by the minimum pressure, or more precisely, the minimum increment of pressure relative to the boundary is sensitive to frequencies of 1000-5000 Hz - here the hearing threshold is the lowest (sound pressure about 2-10 Pa). Toward lower and higher sound frequencies, hearing sensitivity drops sharply.
The pain threshold determines the upper limit of the perception of sound energy and corresponds approximately to a sound intensity of 10 W/m or 130 dB (for a reference signal with a frequency of 1000 Hz).
As sound pressure increases, the intensity of the sound also increases, and the auditory sensation increases in leaps, called the intensity discrimination threshold. The number of these jumps at medium frequencies is approximately 250, at low and high frequencies it decreases and on average over the frequency range is about 150.

Since the range of intensity changes is 130 dB, the elementary jump in sensations on average over the amplitude range is 0.8 dB, which corresponds to a change in sound intensity by 1.2 times. At low hearing levels these jumps reach 2-3 dB, at high levels they decrease to 0.5 dB (1.1 times). An increase in the power of the amplification path by less than 1.44 times is practically not detected by the human ear. With a lower sound pressure developed by the loudspeaker, even doubling the power of the output stage may not produce a noticeable result.

Subjective sound characteristics

The quality of sound transmission is assessed based on auditory perception. Therefore, it is possible to correctly determine the technical requirements for the sound transmission path or its individual links only by studying the patterns connecting the subjectively perceived sensation of sound and the objective characteristics of sound are height, volume and timbre.
The concept of pitch implies a subjective assessment of the perception of sound across the frequency range. Sound is usually characterized not by frequency, but by pitch.
A tone is a signal of a certain pitch that has a discrete spectrum (musical sounds, vowel sounds of speech). A signal that has a wide continuous spectrum, all frequency components of which have the same average power, is called white noise.

A gradual increase in the frequency of sound vibrations from 20 to 20,000 Hz is perceived as a gradual change in tone from the lowest (bass) to the highest.
The degree of accuracy with which a person determines the pitch of a sound by ear depends on the acuity, musicality and training of his ear. It should be noted that the pitch of a sound depends to some extent on the intensity of the sound (at high levels, sounds of greater intensity appear lower than weaker ones.
The human ear can clearly distinguish two tones that are close in pitch. For example, in the frequency range of approximately 2000 Hz, a person can distinguish between two tones that differ from each other in frequency by 3-6 Hz.
The subjective scale of sound perception in frequency is close to the logarithmic law. Therefore, doubling the vibration frequency (regardless of the initial frequency) is always perceived as the same change in pitch. The height interval corresponding to a 2-fold change in frequency is called an octave. The range of frequencies perceived by humans is 20-20,000 Hz, which covers approximately ten octaves.
An octave is a fairly large interval of change in pitch; a person distinguishes significantly smaller intervals. Thus, in ten octaves perceived by the ear, more than a thousand gradations of pitch can be distinguished. Music uses smaller intervals called semitones, which correspond to a change in frequency of approximately 1.054 times.
An octave is divided into half octaves and a third of an octave. For the latter, the following range of frequencies is standardized: 1; 1.25; 1.6; 2; 2.5; 3; 3.15; 4; 5; 6.3:8; 10, which are the boundaries of one-third octaves. If these frequencies are placed at equal distances along the frequency axis, you get a logarithmic scale. Based on this, all frequency characteristics of sound transmission devices are plotted on a logarithmic scale.
The loudness of the transmission depends not only on the intensity of the sound, but also on the spectral composition, the conditions of perception and the duration of exposure. Thus, two sounding tones of medium and low frequency, having the same intensity (or the same sound pressure), are not perceived by a person as equally loud. Therefore, the concept of loudness level in backgrounds was introduced to designate sounds of the same loudness. The sound volume level in the backgrounds is taken to be the sound pressure level in decibels of the same volume of a pure tone with a frequency of 1000 Hz, i.e. for a frequency of 1000 Hz the volume levels in backgrounds and decibels are the same. At other frequencies, sounds may appear louder or quieter at the same sound pressure.
The experience of sound engineers in recording and editing musical works shows that in order to better detect sound defects that may arise during work, the volume level during control listening should be maintained high, approximately corresponding to the volume level in the hall.
With prolonged exposure to intense sound, hearing sensitivity gradually decreases, and the more, the higher the sound volume. The detected decrease in sensitivity is associated with the reaction of hearing to overload, i.e. with its natural adaptation. After some break in listening, hearing sensitivity is restored. It should be added to this that the hearing aid, when perceiving high-level signals, introduces its own, so-called subjective, distortions (which indicates the nonlinearity of hearing). Thus, at a signal level of 100 dB, the first and second subjective harmonics reach levels of 85 and 70 dB.
A significant level of volume and the duration of its exposure cause irreversible phenomena in the auditory organ. It has been noted that young people's hearing thresholds have increased sharply in recent years. The reason for this was a passion for pop music, characterized by high sound volume levels.
The volume level is measured using an electroacoustic device - a sound level meter. The sound being measured is first converted into electrical vibrations by the microphone. After amplification by a special voltage amplifier, these oscillations are measured with a pointer instrument adjusted in decibels. In order for the device readings to correspond as accurately as possible to the subjective perception of loudness, the device is equipped with special filters that change its sensitivity to the perception of sound of different frequencies in accordance with the characteristics of hearing sensitivity.
An important characteristic of sound is timbre. The ability of hearing to distinguish it allows you to perceive signals with a wide variety of shades. The sound of each of the instruments and voices, thanks to their characteristic shades, becomes multicolored and well recognizable.
Timbre, being a subjective reflection of the complexity of the perceived sound, has no quantitative assessment and is characterized by qualitative terms (beautiful, soft, juicy, etc.). When transmitting a signal along an electroacoustic path, the resulting distortions primarily affect the timbre of the reproduced sound. The condition for the correct transmission of the timbre of musical sounds is the undistorted transmission of the signal spectrum. The signal spectrum is the collection of sinusoidal components of a complex sound.
The simplest spectrum is the so-called pure tone; it contains only one frequency. The sound of a musical instrument is more interesting: its spectrum consists of the frequency of the fundamental tone and several “impurity” frequencies called overtones (higher tones). Overtones are a multiple of the frequency of the fundamental tone and are usually smaller in amplitude.
The timbre of the sound depends on the distribution of intensity over overtones. The sounds of different musical instruments vary in timbre.
More complex is the spectrum of combinations of musical sounds called a chord. In such a spectrum there are several fundamental frequencies along with corresponding overtones
Differences in timbre are mainly due to the low-mid frequency components of the signal, therefore, a large variety of timbres is associated with signals lying in the lower part of the frequency range. Signals belonging to its upper part, as they increase, increasingly lose their timbre coloring, which is due to the gradual departure of their harmonic components beyond the limits of audible frequencies. This can be explained by the fact that up to 20 or more harmonics are actively involved in the formation of the timbre of low sounds, medium 8 - 10, high 2 - 3, since the rest are either weak or fall outside the range of audible frequencies. Therefore, high sounds, as a rule, are poorer in timbre.
Almost all natural sound sources, including sources of musical sounds, have a specific dependence of timbre on volume level. Hearing is also adapted to this dependence - it is natural for it to determine the intensity of a source by the color of the sound. Louder sounds are usually more harsh.

Musical sound sources

A number of factors characterizing the primary sound sources have a great influence on the sound quality of electroacoustic systems.
The acoustic parameters of musical sources depend on the composition of the performers (orchestra, ensemble, group, soloist and type of music: symphonic, folk, pop, etc.).

The origin and formation of sound on each musical instrument has its own specifics associated with the acoustic characteristics of sound production in a particular musical instrument.
An important element of musical sound is attack. This is a specific transition process during which stable sound characteristics are established: volume, timbre, pitch. Any musical sound goes through three stages - beginning, middle and end, and both the initial and final stages have a certain duration. The initial stage is called an attack. It lasts differently: for plucked instruments, percussion and some wind instruments it lasts 0-20 ms, for the bassoon it lasts 20-60 ms. An attack is not just an increase in the volume of a sound from zero to some steady value; it can be accompanied by the same change in the pitch of the sound and its timbre. Moreover, the attack characteristics of the instrument are not the same in different parts of its range with different playing styles: the violin is the most perfect instrument in terms of the wealth of possible expressive methods of attack.
One of the characteristics of any musical instrument is its frequency range. In addition to the fundamental frequencies, each instrument is characterized by additional high-quality components - overtones (or, as is customary in electroacoustics, higher harmonics), which determine its specific timbre.
It is known that sound energy is unevenly distributed across the entire spectrum of sound frequencies emitted by a source.
Most instruments are characterized by amplification of fundamental frequencies, as well as individual overtones, in certain (one or more) relatively narrow frequency bands (formants), different for each instrument. Resonant frequencies (in hertz) of the formant region are: for trumpet 100-200, horn 200-400, trombone 300-900, trumpet 800-1750, saxophone 350-900, oboe 800-1500, bassoon 300-900, clarinet 250-600 .
Another characteristic property of musical instruments is the strength of their sound, which is determined by the greater or lesser amplitude (span) of their sounding body or air column (a greater amplitude corresponds to a stronger sound and vice versa). The peak acoustic power values ​​(in watts) are: for large orchestra 70, bass drum 25, timpani 20, snare drum 12, trombone 6, piano 0.4, trumpet and saxophone 0.3, trumpet 0.2, double bass 0.( 6, small flute 0.08, clarinet, horn and triangle 0.05.
The ratio of the sound power extracted from an instrument when played “fortissimo” to the power of sound when played “pianissimo” is usually called the dynamic range of the sound of musical instruments.
The dynamic range of a musical sound source depends on the type of performing group and the nature of the performance.
Let's consider the dynamic range of individual sound sources. The dynamic range of individual musical instruments and ensembles (orchestras and choirs of various compositions), as well as voices, is understood as the ratio of the maximum sound pressure created by a given source to the minimum, expressed in decibels.
In practice, when determining the dynamic range of a sound source, one usually operates only on sound pressure levels, calculating or measuring their corresponding difference. For example, if the maximum sound level of an orchestra is 90 and the minimum is 50 dB, then the dynamic range is said to be 90 - 50 = 40 dB. In this case, 90 and 50 dB are sound pressure levels relative to zero acoustic level.
The dynamic range for a given sound source is not a constant value. It depends on the nature of the work being performed and on the acoustic conditions of the room in which the performance takes place. Reverberation expands the dynamic range, which typically reaches its maximum in rooms with large volumes and minimal sound absorption. Almost all instruments and human voices have an uneven dynamic range across sound registers. For example, the volume level of the lowest sound on a forte for a vocalist is equal to the level of the highest sound on a piano.

The dynamic range of a particular musical program is expressed in the same way as for individual sound sources, but the maximum sound pressure is noted with a dynamic ff (fortissimo) tone, and the minimum with a pp (pianissimo).

The highest volume, indicated in the notes fff (forte, fortissimo), corresponds to an acoustic sound pressure level of approximately 110 dB, and the lowest volume, indicated in the notes ppr (piano-pianissimo), approximately 40 dB.
It should be noted that the dynamic nuances of performance in music are relative and their relationship with the corresponding sound pressure levels is to some extent conditional. The dynamic range of a particular musical program depends on the nature of the composition. Thus, the dynamic range of classical works by Haydn, Mozart, Vivaldi rarely exceeds 30-35 dB. The dynamic range of pop music usually does not exceed 40 dB, while that of dance and jazz music is only about 20 dB. Most works for orchestra of Russian folk instruments also have a small dynamic range (25-30 dB). This is also true for a brass band. However, the maximum sound level of a brass band in a room can reach a fairly high level (up to 110 dB).

Masking effect

The subjective assessment of loudness depends on the conditions in which the sound is perceived by the listener. In real conditions, an acoustic signal does not exist in absolute silence. At the same time, extraneous noise affects the hearing, complicating sound perception, masking to a certain extent the main signal. The effect of masking a pure sine wave by extraneous noise is measured by the value indicating. by how many decibels the threshold of audibility of the masked signal increases above the threshold of its perception in silence.
Experiments to determine the degree of masking of one sound signal by another show that a tone of any frequency is masked by lower tones much more effectively than by higher ones. For example, if two tuning forks (1200 and 440 Hz) emit sounds with the same intensity, then we stop hearing the first tone, it is masked by the second (by extinguishing the vibration of the second tuning fork, we will hear the first again).
If two complex sound signals consisting of certain sound frequency spectra exist simultaneously, then a mutual masking effect occurs. Moreover, if the main energy of both signals lies in the same region of the audio frequency range, then the masking effect will be the strongest. Thus, when transmitting an orchestral piece, due to masking by the accompaniment, the soloist’s part may become poorly intelligible and inaudible.
Achieving clarity or, as they say, “transparency” of sound in the sound transmission of orchestras or pop ensembles becomes very difficult if an instrument or individual groups of orchestra instruments play in one or similar registers at the same time.
The director, when recording an orchestra, must take into account the features of camouflage. At rehearsals, with the help of the conductor, he establishes a balance between the sound strength of the instruments of one group, as well as between the groups of the entire orchestra. The clarity of the main melodic lines and individual musical parts is achieved in these cases by the close placement of microphones to the performers, the deliberate selection by the sound engineer of the most important instruments in a given place of the work, and other special sound engineering techniques.
The phenomenon of masking is opposed by the psychophysiological ability of the hearing organs to single out from the general mass of sounds one or more that carry the most important information. For example, when an orchestra is playing, the conductor notices the slightest inaccuracies in the performance of a part on any instrument.
Masking can significantly affect the quality of signal transmission. A clear perception of the received sound is possible if its intensity significantly exceeds the level of interference components located in the same band as the received sound. With uniform interference, the signal excess should be 10-15 dB. This feature of auditory perception finds practical application, for example, in assessing the electroacoustic characteristics of media. So, if the signal-to-noise ratio of an analog record is 60 dB, then the dynamic range of the recorded program can be no more than 45-48 dB.

Temporal characteristics of auditory perception

The hearing aid, like any other oscillatory system, is inertial. When the sound disappears, the auditory sensation does not disappear immediately, but gradually, decreasing to zero. The time during which the noise level decreases by 8-10 backgrounds is called the hearing time constant. This constant depends on a number of circumstances, as well as on the parameters of the perceived sound. If two short sound pulses arrive to the listener, identical in frequency composition and level, but one of them is delayed, then they will be perceived together with a delay not exceeding 50 ms. At large delay intervals, both impulses are perceived separately, and an echo occurs.
This feature of hearing is taken into account when designing some signal processing devices, for example, electronic delay lines, reverberates, etc.
It should be noted that, due to the special property of hearing, the sensation of the volume of a short-term sound pulse depends not only on its level, but also on the duration of the pulse’s impact on the ear. Thus, a short-term sound, lasting only 10-12 ms, is perceived by the ear quieter than a sound of the same level, but affecting the hearing for, for example, 150-400 ms. Therefore, when listening to a broadcast, loudness is the result of averaging the energy of the sound wave over a certain interval. In addition, human hearing has inertia, in particular, when perceiving nonlinear distortions, it does not feel them if the duration of the sound pulse is less than 10-20 ms. That is why in level indicators of sound recording household radio-electronic equipment, the instantaneous signal values ​​are averaged over a period selected in accordance with the temporal characteristics of the hearing organs.

Spatial representation of sound

One of the important human abilities is the ability to determine the direction of a sound source. This ability is called the binaural effect and is explained by the fact that a person has two ears. Experimental data shows where the sound comes from: one for high-frequency tones, one for low-frequency tones.

The sound travels a shorter distance to the ear facing the source than to the other ear. As a result, the pressure of sound waves in the ear canals varies in phase and amplitude. The amplitude differences are significant only at high frequencies, when the sound wavelength becomes comparable to the size of the head. When the difference in amplitude exceeds a threshold value of 1 dB, the sound source appears to be on the side where the amplitude is greater. The angle of deviation of the sound source from the center line (line of symmetry) is approximately proportional to the logarithm of the amplitude ratio.
To determine the direction of a sound source with frequencies below 1500-2000 Hz, phase differences are significant. It seems to a person that the sound comes from the side from which the wave, which is ahead in phase, reaches the ear. The angle of deviation of sound from the midline is proportional to the difference in the time of arrival of sound waves to both ears. A trained person can notice a phase difference with a time difference of 100 ms.
The ability to determine the direction of sound in the vertical plane is much less developed (about 10 times). This physiological feature is associated with the orientation of the hearing organs in the horizontal plane.
A specific feature of spatial perception of sound by a person is manifested in the fact that the hearing organs are able to sense the total, integral localization created with the help of artificial means of influence. For example, in a room, two speakers are installed along the front at a distance of 2-3 m from each other. The listener is located at the same distance from the axis of the connecting system, strictly in the center. In a room, two sounds of equal phase, frequency and intensity are emitted through the speakers. As a result of the identity of the sounds passing into the organ of hearing, a person cannot separate them; his sensations give ideas about a single, apparent (virtual) sound source, which is located strictly in the center on the axis of symmetry.
If we now reduce the volume of one speaker, the apparent source will move towards the louder speaker. The illusion of a sound source moving can be obtained not only by changing the signal level, but also by artificially delaying one sound relative to another; in this case, the apparent source will shift towards the speaker emitting the signal in advance.
To illustrate integral localization, we give an example. The distance between the speakers is 2 m, the distance from the front line to the listener is 2 m; in order for the source to move 40 cm to the left or right, it is necessary to submit two signals with a difference in intensity level of 5 dB or with a time delay of 0.3 ms. With a level difference of 10 dB or a time delay of 0.6 ms, the source will “move” 70 cm from the center.
Thus, if you change the sound pressure created by the speaker, the illusion of moving the sound source arises. This phenomenon is called summary localization. To create summary localization, a two-channel stereophonic sound transmission system is used.
Two microphones are installed in the primary room, each of which works on its own channel. The secondary has two loudspeakers. The microphones are located at a certain distance from each other along a line parallel to the placement of the sound emitter. When moving the sound emitter, different sound pressure will act on the microphone and the time of arrival of the sound wave will be different due to the unequal distance between the sound emitter and the microphones. This difference creates a total localization effect in the secondary room, as a result of which the apparent source is localized at a certain point in space located between two loudspeakers.
It should be said about the binaural sound transmission system. With this system, called an artificial head system, two separate microphones are placed in the primary room, spaced at a distance from each other equal to the distance between a person's ears. Each of the microphones has an independent sound transmission channel, the output of which in the secondary room includes telephones for the left and right ears. If the sound transmission channels are identical, such a system accurately conveys the binaural effect created near the ears of the “artificial head” in the primary room. Having headphones and having to use them for a long time is a disadvantage.
The organ of hearing determines the distance to the sound source using a number of indirect signs and with some errors. Depending on whether the distance to the signal source is small or large, its subjective assessment changes under the influence of various factors. It was found that if the determined distances are small (up to 3 m), then their subjective assessment is almost linearly related to the change in the volume of the sound source moving along the depth. An additional factor for a complex signal is its timbre, which becomes increasingly “heavier” as the source approaches the listener. This is due to the increasing amplification of low overtones compared to high overtones, caused by the resulting increase in volume level.
For average distances of 3-10 m, moving the source away from the listener will be accompanied by a proportional decrease in volume, and this change will apply equally to the fundamental frequency and harmonic components. As a result, there is a relative strengthening of the high-frequency part of the spectrum and the timbre becomes brighter.
As the distance increases, energy losses in the air will increase in proportion to the square of the frequency. Increased loss of high register overtones will result in decreased timbral brightness. Thus, the subjective assessment of distances is associated with changes in its volume and timbre.
In a closed room, the signals of the first reflections, delayed relative to the direct reflection by 20-40 ms, are perceived by the hearing organ as coming from different directions. At the same time, their increasing delay creates the impression of a significant distance from the points from which these reflections occur. Thus, by the delay time one can judge the relative distance of secondary sources or, what is the same, the size of the room.

Some features of the subjective perception of stereophonic broadcasts.

A stereophonic sound transmission system has a number of significant features compared to a conventional monophonic one.
The quality that distinguishes stereophonic sound, volume, i.e. natural acoustic perspective can be assessed using some additional indicators that do not make sense with a monophonic sound transmission technique. Such additional indicators include: hearing angle, i.e. the angle at which the listener perceives the stereophonic sound picture; stereo resolution, i.e. subjectively determined localization of individual elements of the sound image at certain points in space within the audibility angle; acoustic atmosphere, i.e. the effect of giving the listener a feeling of presence in the primary room where the transmitted sound event occurs.

On the role of room acoustics

Colorful sound is achieved not only with the help of sound reproduction equipment. Even with fairly good equipment, the sound quality may be poor if the listening room does not have certain properties. It is known that in a closed room a nasal sound phenomenon called reverberation occurs. By affecting the organs of hearing, reverberation (depending on its duration) can improve or worsen sound quality.

A person in a room perceives not only direct sound waves created directly by the sound source, but also waves reflected by the ceiling and walls of the room. Reflected waves are heard for some time after the sound source has stopped.
It is sometimes believed that reflected signals only play a negative role, interfering with the perception of the main signal. However, this idea is incorrect. A certain part of the energy of the initial reflected echo signals, reaching the human ears with short delays, amplifies the main signal and enriches its sound. In contrast, later reflected echoes. whose delay time exceeds a certain critical value, form a sound background that makes it difficult to perceive the main signal.
The listening room should not have a long reverberation time. Living rooms, as a rule, have little reverberation due to their limited size and the presence of sound-absorbing surfaces, upholstered furniture, carpets, curtains, etc.
Obstacles of different nature and properties are characterized by a sound absorption coefficient, which is the ratio of the absorbed energy to the total energy of the incident sound wave.

To increase the sound-absorbing properties of the carpet (and reduce noise in the living room), it is advisable to hang the carpet not close to the wall, but with a gap of 30-50 mm).

IN mechanism of sound perception Various structures take part: sound waves, which are vibrations of air molecules, propagate from the sound source, are captured by the external ear, amplified by the middle ear and transformed by the inner ear into nerve impulses entering the brain.

The movement of the perilymph causes the main membrane that makes up the surface of the helix, where the organ of Corti is located, to vibrate. When sensory cells are moved by vibration, small cilia on their surface brush against the membrane and produce metabolic changes that transform the mechanical stimuli into nerves, transmitted along the cochlear nerve and reaching the auditory nerve, from where they enter the brain, where they are recognized and perceived as sounds.

FUNCTIONS OF THE BONES OF THE MIDDLE EAR.

When the eardrum vibrates, the ossicles of the middle ear also move: each vibration causes the hammer to move, which moves the incus, which transmits the movement to the stapes, then the base of the stapes strikes the oval window and thus creates a wave in the fluid contained in the inner ear. Because the eardrum has a larger surface area than the oval window, sound is concentrated and amplified as it passes through the bones of the middle ear to compensate for energy losses during the transition of sound waves from air to liquid. Thanks to this mechanism, very faint sounds can be perceived.

The human ear can perceive sound waves that have certain characteristics of intensity and frequency. In terms of frequency, humans can detect sounds in the range of 16,000 to 20,000 hertz (vibrations per second), and human hearing is especially sensitive to the human voice, which ranges from 1,000 to 4,000 hertz. The intensity, which depends on the amplitude of the sound waves, must have a certain threshold, namely 10 decibels: sounds below this mark are not perceived by the ear.