hearing aid

Sounds are perceived through the auditory apparatus that receives sound waves, which are converted into movements of the otic osteocytes and perceived in the inner ear, which in turn transmits them through the nervous system to the brain. You have this ability even before you are born.

human voice

The human voice is produced by the vibration of the vocal cords, which generates a sound wave that is a combination of several frequencies and their corresponding harmonics. The oral-nasal cavity serves to create quasi-stationary waves, which is why certain frequencies called formants appear. Each speech sound segment is characterized by a certain frequency spectrum or distribution of sound energy at different frequencies. The human ear is capable of identifying different formants of said sound and perceiving each sound with different formants as qualitatively different, which is what allows, for example, to distinguish two vowels. Typically the first, lowest frequency formant is related to the vowel opening which is ultimately related to the frequency of the standing waves vibrating vertically in the cavity. The second formant is related to vibration in the horizontal direction and is related to whether the vowel is front, central or back.

The male voice has a fundamental pitch between , while the female voice is higher, typically between . Children's voices are even higher pitched. Without the resonance filtering produced by the oral-nasal cavity, our sound emissions would not have the necessary clarity to be audible. This filtering process is precisely what allows us to generate the various formants of each segmental unit of speech.

speech sounds

Human languages ​​use recognizable homogeneous segments, a few tens of milliseconds long, that make up speech sounds, technically called phones. Linguistically, not all acoustic differences are relevant, for example, women and children generally have higher pitches, so all the sounds they produce have on average a higher and more intense fundamental frequency and harmonics.

Proficient speakers of a language learn to “classify” different qualitatively similar sounds into relevant feature equivalence classes. These equivalence classes recognized by speakers are the mental constructs we call phonemes. Most natural languages ​​have a few dozen distinctive phonemes, although the acoustic variations of phones and sounds are enormous.

El sonido, en combinación con el silencio "Silencio (sonido)"), es la materia prima de la música. En la música los sonidos se califican en categorías como: largos y cortos, fuertes y débiles, agudos y graves, agradables y desagradables. El sonido ha estado siempre presente en la vida cotidiana del hombre. A lo largo de la historia el ser humano ha inventado una serie de reglas para ordenarlo hasta construir algún tipo de lenguaje musical.

Properties

The four basic qualities of sound are pitch, duration, intensity, and timbre or color.

The pitch, or pitch, indicates whether the sound is low, high or medium, and is determined by the fundamental frequency of the sound waves, measured in cycles per second or hertz (Hz).

• - slow vibration = low frequency = low sound.

• - fast vibration = high frequency = high pitched sound.

For humans to be able to perceive a sound, it must be between the hearing range of 20 and 20,000 Hz. Below this range we have infrasound and above it we have ultrasound. This is called the audible frequency range. The older you are, the less this range reduces in both bass and treble.

In Western music, certain tones called notes were established, whose sequence of 12 (C, C#, D, D#, E, F, F#, G, G#, A, A#, B) is repeated forming octaves, in each of which the frequency is doubled. The difference between different notes is called the interval.

It is the time during which a sound is maintained. We can hear long, short, very short sounds, etc.

The only acoustic instruments that can maintain sounds for as long as they want are those with bowed strings, like the violin, and wind instruments (using circular or continuous breathing); But in general, wind instruments depend on lung capacity, and string instruments depend on the change in the bow produced by the player.

Sound takes between 12 and 15 hundredths of a second to reach the brain. If the duration is shorter, there is no time for the height to be recognized, producing a clicking sensation called click.

It is the amount of acoustic energy that a sound contains, that is, how loud or soft a sound is. Intensity is determined by power, which in turn is determined by amplitude "Amplitude (sound)") and allows us to distinguish whether the sound is strong or weak.

Sound intensity is divided into physical intensity and auditory intensity, the former being determined by the amount of energy that propagates, in unit time, through the unit area perpendicular to the direction in which the wave propagates. And the auditory intensity is based on the Weber-Fechner psychophysical law, which establishes a logarithmic relationship between the physical intensity of the sound that is captured and the minimum physical intensity audible to the human ear.

The sounds we perceive must exceed the hearing threshold (0 dB) and not reach the pain threshold (130 dB). We measure this quality with the sound level meter and the results are expressed in decibels (dB) in honor of the scientist and inventor Alexander Graham Bell.

Intensity also has to do with directionality, since it is directly related to distance.

In musical notation, intensity is usually indicated with the following traditional terms, from Italian:.

1. • fortissimo or very strong.

2. • strong or strong.

3. • mezzoforte or moderately strong.

4. • mezzopiano or moderately soft.

5. • piano "Piano (dynamics)") or soft.

6. • pianissimo or very soft.

Timbre is the quality of sound that allows the identification of its sound source.

The same note sounds different if it is played by a flute, a violin, a trumpet, etc. Each instrument has a timbre that identifies it or differentiates it from the others. The quality of the material used to emit the sound also influences the variation in timbre. The same thing happens with the voice. The sound emitted by a man, a woman, a child has a different timbre. The timbre allows you to distinguish whether the voice is rough, sweet, hoarse or velvety. Thus, the sound will be clear, dull, pleasant or annoying. Timbre is a characteristic of sound that allows us to differentiate two sounds that have the same pitch, the same duration and the same sound intensity depending on the sound source. Timbre is a component of a sound that is given by the quantity and intensity of the different harmonics that compose it, as well as the shape of the sound wave, and specifically the envelope "Envelope (waves)") of amplitude.

Sound is a type of longitudinal mechanical waves produced by pressure variations of the medium. These pressure variations (captured by the human ear) produce the perception of sound in the brain.

There are sounds generated by different sources in nature and their characteristics of frequency (height), intensity (strength), wave shape (timbre) and envelope (modulation) make them different and unmistakable. For example, the soft flow of water through a tap has the same characteristics in frequency, timbre and envelope as the deafening flow of water in the Iguazú Falls, with its approximately 100 meters of free fall height, but the intensity (always measured in decibels at a meter distance from the crash zone) is much greater.

Of the requirements noted, that of the envelope is the most significant, since it is "the variation of intensity during a time, generally the initial one, considered." The example of the difference in envelopes is the clear perception we have when some instrument with scraped strings (violin, cello) are played "normally" with the bow rubbing the strings or when they are plucked (pizzicato); While in the first case the sound has approximately the same intensity throughout its execution, in the second case the sound starts with a maximum intensity (the tense string released by the musician) quickly attenuating with the passage of time and in an exponential manner, so that the oscillation following the previous one follows a law of descending variation. Among the instruments that exhibit a constant envelope we have primarily the pipe organ (and its electronic copies), the saxophone (also air, like the organ) and those instruments that, not having a fixed envelope, can easily control this function, such as the flute (recorder and harmonica), the tuba, the clarinet and the trumpets, fife and whistles, transportation horns (warning instruments); Among the instruments of exponential declension we have all the percussion instruments that form the "drums": bass drums, cymbals, snare drums, tumbadoras (in this branch we must highlight the cymbals, with a long declination time that can be violently cut by the musician) using a pedal or even the hand.

Los humanos y otros animales percibimos el sonido a mediante el sentido "Sentido (percepción)") del oído, pero además podemos percibir sonidos de baja frecuencia a través de otras partes del cuerpo. Generalmente se considera que los sonidos audibles para el oído humano son los que tienen una frecuencia comprendida entre los 20 y los 20 000 Hz,[2]​ pero estos límites no están claramente definidos (por ejemplo, en la banda inferior hay quien considera valores inferiores como 12 Hz),[3]​ y es bien sabido que el límite superior disminuye con la edad. Por encima y por debajo de este rango están los ultrasonidos y los infrasonidos, respectivamente. Otras especies de animales pueden percibir otros rangos de frecuencias:[4]​ el gato doméstico 100-32 000 Hz; el elefante africano 16-12 000 Hz; el murciélago 1000-150 000 Hz o los roedores 70-150 000 Hz. Es muy conocido el ejemplo de los perros (40-46 000 Hz), que pueden escuchar sonidos a frecuencias por encima de los 20 000 Hz que son imperceptibles por los humanos (hay silbatos que emiten ultrasonidos que son utilizados tanto para adiestrar como para asustar los perros, pero hay quién piensa que también se puede utilizar para dispersar a grupos de jóvenes).

Para muchos animales el sentido del oído es capital para su supervivencia, ya que utilizan los sonidos para detectar peligros, a la depredación detectando las presas o para comunicación. La mayoría de fenómenos que se producen en la Tierra tienen asociados sonidos característicos: la lluvia, las olas"), el fuego, el viento, etc. Muchas especies, tanto mamíferos, anfibios como la rana o los pájaros, han desarrollado órganos "Órgano (anatomía)") especiales para la producción de sonidos, que en el caso de algunos pájaros ha evolucionado hasta el canto o hasta el habla humana. Los humanos incluso hemos desarrollado una cultura y una tecnología basada en la generación y la transmisión de sonidos (cultura de transmisión oral, teléfono, radio "Radio (medio de comunicación)"), fonógrafo, disco compacto, etc.).

Para la medida del sonido se utiliza una escala logarítmica,[5]​ que permite representar magnitudes muy grandes y muy pequeñas con números relativamente pequeños, y que es una cifra adimensional porque es una relación entre dos magnitudes con las mismas dimensiones, la presión sonora respecto de una presión sonora arbitraria de referencia que, por convenio internacional, son los 2 micropascales. Se trata de la escala de decibelios, que expresa la magnitud del sonido en decibelios, décima parte del belio, una unidad raramente utilizada. El origen de la escala, el valor 0, corresponde al umbral auditivo humano (2 μPa), de forma que los valores negativos corresponderían a sonidos imperceptibles por el hombre. El decibelio no es una unidad incluida en el Sistema Internacional de Unidades (hay científicos que no la consideran una unidad),[6]​ aun así es aceptado para utilizarse junto con las unidades del SI.[7]​.

sound pressure level

The sound pressure level or sound level is a logarithmic measure of the effective sound pressure of a mechanical wave with respect to a reference source. It is measured in decibels:

where p is the reference sound pressure (in air it is customary to consider µPa, and p is the value of the effective pressure that we want to measure.

If the propagation medium is air, the sound pressure level (SPL) is almost always expressed in decibels with respect to the reference pressure of 20 μPa, generally considered the threshold of audibility for human beings (approximately equivalent to the sound pressure produced by a mosquito flying three meters away). Measurements of audio equipment are almost always made in reference to this value. However, in other media, such as water, a reference pressure equal to μPa is often used.[8] In general, it is necessary to know the reference level when comparing SPL measurements and the fact that the unit dB (*SPL) is often abbreviated as dB can be misleading, since it is a relative measurement.

Considering the range of human perception (from 20 µPa to 20,000 Pa) on the decibel scale, perceptible sounds are between 0 and 180 decibels (dB) - The following table shows some examples:.

Sound intensity level

The sound intensity level or acoustic intensity level (L) is a logarithmic measurement of the sound intensity (measured in W/m²) compared to a reference value (10 W/m²). The relationship is defined as:[9]​.

where I is the sound intensity in W/m², and I is the reference value, which corresponds to the lowest sound intensity audible to the human ear at a frequency of 1000 Hz. The sound intensity level is a dimensionless value and is expressed in decibels (dB).

On the other hand, if instead of taking the threshold intensity at 1000 Hz, we take the real threshold intensity for each frequency, then we would talk about loudness and it would be expressed in phons,[9]​ the unit of measurement of the intensity of the sound sensation for the human ear.

The sensation that a sound produces in us is subjective and depends on the observer. There is no proportional relationship between the physical intensity of a sound and the sound sensation or loudness that it produces in us; the sound sensation approximately follows the Weber-Fechner law, which tells us that the sound sensation follows an arithmetic progression while the sound stimulus follows a geometric progression.[10]​.

Noise pollution or noise pollution is the excess of sound that alters the normal conditions of the environment in a certain area. Although noise does not accumulate, move or last over time like other pollution, it can also cause great damage to people's quality of life if it is not controlled well or adequately.

The term "noise pollution" refers to noise (understood as excessive and annoying sound), caused by human activities (traffic, industries, leisure venues, airplanes, ships, among others) that produces negative effects on the hearing, physical and mental health of living beings.

This term is closely related to noise because this occurs when noise is considered a pollutant, that is, an annoying sound that can produce harmful physiological effects such as decreased hearing ability or deafness and psychological effects for a person or group of people.

The World Health Organization (WHO) considers 70 dB (A) as the desirable upper limit. Different countries have health standards on acceptable limits both in the social environment and in the work environment, as well as measures to reduce noise pollution.

• - Acoustics.

• - Digital audio.

• - High-end audio.

• - Noise pollution.

• - Surround sound.

• - Silence (sound) "Silence (sound)").

• - Volume (sound) "Volume (sound)").

• - Buzz.

• - M. Crocker (editor), 1994. Encyclopedia of Acoustics (Interscience).

• - Farina, Angelo; Tronchin, Lamberto (2004). Advanced techniques for measuring and reproducing spatial sound properties of auditing. Proc. of International Symposium on Room Acoustics Design and Science (RADS), 11–13 April 2004, Kyoto, Japan. Article.

• - L. E. Kinsler, A. R. Frey, A. B. Coppens, and J. V. Sanders, 1999. Fundamentals of Acoustics, fourth edition (Wiley).

• - Philip M. Morse and K. Uno Ingard, 1986. Theoretical Acoustics (Princeton University Press). ISBN 0-691-08425-4.

• - Allan D. Pierce, 1989. Acoustics: An Introduction to its Physical Principles and Applications (Acoustical Society of America). ISBN 0-88318-612-8.

• - D. R. Raichel, 2006. The Science and Applications of Acoustics, second edition (Springer). eISBN 0-387-30089-9.

• - E. Skudrzyk, 1971. The Foundations of Acoustics: Basic Mathematics and Basic Acoustics (Springer).

• - Wikimedia Commons hosts a multimedia category on Sound.

• - Wiktionary has definitions and other information about sound.

• - Sound as vibration.

• - The Dictionary of the Royal Spanish Academy has a definition for sound.

hearing aid

Sounds are perceived through the auditory apparatus that receives sound waves, which are converted into movements of the otic osteocytes and perceived in the inner ear, which in turn transmits them through the nervous system to the brain. You have this ability even before you are born.

human voice

The human voice is produced by the vibration of the vocal cords, which generates a sound wave that is a combination of several frequencies and their corresponding harmonics. The oral-nasal cavity serves to create quasi-stationary waves, which is why certain frequencies called formants appear. Each speech sound segment is characterized by a certain frequency spectrum or distribution of sound energy at different frequencies. The human ear is capable of identifying different formants of said sound and perceiving each sound with different formants as qualitatively different, which is what allows, for example, to distinguish two vowels. Typically the first, lowest frequency formant is related to the vowel opening which is ultimately related to the frequency of the standing waves vibrating vertically in the cavity. The second formant is related to vibration in the horizontal direction and is related to whether the vowel is front, central or back.

The male voice has a fundamental pitch between , while the female voice is higher, typically between . Children's voices are even higher pitched. Without the resonance filtering produced by the oral-nasal cavity, our sound emissions would not have the necessary clarity to be audible. This filtering process is precisely what allows us to generate the various formants of each segmental unit of speech.

speech sounds

Human languages ​​use recognizable homogeneous segments, a few tens of milliseconds long, that make up speech sounds, technically called phones. Linguistically, not all acoustic differences are relevant, for example, women and children generally have higher pitches, so all the sounds they produce have on average a higher and more intense fundamental frequency and harmonics.

Proficient speakers of a language learn to “classify” different qualitatively similar sounds into relevant feature equivalence classes. These equivalence classes recognized by speakers are the mental constructs we call phonemes. Most natural languages ​​have a few dozen distinctive phonemes, although the acoustic variations of phones and sounds are enormous.

El sonido, en combinación con el silencio "Silencio (sonido)"), es la materia prima de la música. En la música los sonidos se califican en categorías como: largos y cortos, fuertes y débiles, agudos y graves, agradables y desagradables. El sonido ha estado siempre presente en la vida cotidiana del hombre. A lo largo de la historia el ser humano ha inventado una serie de reglas para ordenarlo hasta construir algún tipo de lenguaje musical.

Properties

The four basic qualities of sound are pitch, duration, intensity, and timbre or color.

The pitch, or pitch, indicates whether the sound is low, high or medium, and is determined by the fundamental frequency of the sound waves, measured in cycles per second or hertz (Hz).

• - slow vibration = low frequency = low sound.

• - fast vibration = high frequency = high pitched sound.

For humans to be able to perceive a sound, it must be between the hearing range of 20 and 20,000 Hz. Below this range we have infrasound and above it we have ultrasound. This is called the audible frequency range. The older you are, the less this range reduces in both bass and treble.

In Western music, certain tones called notes were established, whose sequence of 12 (C, C#, D, D#, E, F, F#, G, G#, A, A#, B) is repeated forming octaves, in each of which the frequency is doubled. The difference between different notes is called the interval.

It is the time during which a sound is maintained. We can hear long, short, very short sounds, etc.

The only acoustic instruments that can maintain sounds for as long as they want are those with bowed strings, like the violin, and wind instruments (using circular or continuous breathing); But in general, wind instruments depend on lung capacity, and string instruments depend on the change in the bow produced by the player.

Sound takes between 12 and 15 hundredths of a second to reach the brain. If the duration is shorter, there is no time for the height to be recognized, producing a clicking sensation called click.

It is the amount of acoustic energy that a sound contains, that is, how loud or soft a sound is. Intensity is determined by power, which in turn is determined by amplitude "Amplitude (sound)") and allows us to distinguish whether the sound is strong or weak.

Sound intensity is divided into physical intensity and auditory intensity, the former being determined by the amount of energy that propagates, in unit time, through the unit area perpendicular to the direction in which the wave propagates. And the auditory intensity is based on the Weber-Fechner psychophysical law, which establishes a logarithmic relationship between the physical intensity of the sound that is captured and the minimum physical intensity audible to the human ear.

The sounds we perceive must exceed the hearing threshold (0 dB) and not reach the pain threshold (130 dB). We measure this quality with the sound level meter and the results are expressed in decibels (dB) in honor of the scientist and inventor Alexander Graham Bell.

Intensity also has to do with directionality, since it is directly related to distance.

In musical notation, intensity is usually indicated with the following traditional terms, from Italian:.

1. • fortissimo or very strong.

2. • strong or strong.

3. • mezzoforte or moderately strong.

4. • mezzopiano or moderately soft.

5. • piano "Piano (dynamics)") or soft.

6. • pianissimo or very soft.

Timbre is the quality of sound that allows the identification of its sound source.

The same note sounds different if it is played by a flute, a violin, a trumpet, etc. Each instrument has a timbre that identifies it or differentiates it from the others. The quality of the material used to emit the sound also influences the variation in timbre. The same thing happens with the voice. The sound emitted by a man, a woman, a child has a different timbre. The timbre allows you to distinguish whether the voice is rough, sweet, hoarse or velvety. Thus, the sound will be clear, dull, pleasant or annoying. Timbre is a characteristic of sound that allows us to differentiate two sounds that have the same pitch, the same duration and the same sound intensity depending on the sound source. Timbre is a component of a sound that is given by the quantity and intensity of the different harmonics that compose it, as well as the shape of the sound wave, and specifically the envelope "Envelope (waves)") of amplitude.

Sound is a type of longitudinal mechanical waves produced by pressure variations of the medium. These pressure variations (captured by the human ear) produce the perception of sound in the brain.

There are sounds generated by different sources in nature and their characteristics of frequency (height), intensity (strength), wave shape (timbre) and envelope (modulation) make them different and unmistakable. For example, the soft flow of water through a tap has the same characteristics in frequency, timbre and envelope as the deafening flow of water in the Iguazú Falls, with its approximately 100 meters of free fall height, but the intensity (always measured in decibels at a meter distance from the crash zone) is much greater.

Of the requirements noted, that of the envelope is the most significant, since it is "the variation of intensity during a time, generally the initial one, considered." The example of the difference in envelopes is the clear perception we have when some instrument with scraped strings (violin, cello) are played "normally" with the bow rubbing the strings or when they are plucked (pizzicato); While in the first case the sound has approximately the same intensity throughout its execution, in the second case the sound starts with a maximum intensity (the tense string released by the musician) quickly attenuating with the passage of time and in an exponential manner, so that the oscillation following the previous one follows a law of descending variation. Among the instruments that exhibit a constant envelope we have primarily the pipe organ (and its electronic copies), the saxophone (also air, like the organ) and those instruments that, not having a fixed envelope, can easily control this function, such as the flute (recorder and harmonica), the tuba, the clarinet and the trumpets, fife and whistles, transportation horns (warning instruments); Among the instruments of exponential declension we have all the percussion instruments that form the "drums": bass drums, cymbals, snare drums, tumbadoras (in this branch we must highlight the cymbals, with a long declination time that can be violently cut by the musician) using a pedal or even the hand.

Los humanos y otros animales percibimos el sonido a mediante el sentido "Sentido (percepción)") del oído, pero además podemos percibir sonidos de baja frecuencia a través de otras partes del cuerpo. Generalmente se considera que los sonidos audibles para el oído humano son los que tienen una frecuencia comprendida entre los 20 y los 20 000 Hz,[2]​ pero estos límites no están claramente definidos (por ejemplo, en la banda inferior hay quien considera valores inferiores como 12 Hz),[3]​ y es bien sabido que el límite superior disminuye con la edad. Por encima y por debajo de este rango están los ultrasonidos y los infrasonidos, respectivamente. Otras especies de animales pueden percibir otros rangos de frecuencias:[4]​ el gato doméstico 100-32 000 Hz; el elefante africano 16-12 000 Hz; el murciélago 1000-150 000 Hz o los roedores 70-150 000 Hz. Es muy conocido el ejemplo de los perros (40-46 000 Hz), que pueden escuchar sonidos a frecuencias por encima de los 20 000 Hz que son imperceptibles por los humanos (hay silbatos que emiten ultrasonidos que son utilizados tanto para adiestrar como para asustar los perros, pero hay quién piensa que también se puede utilizar para dispersar a grupos de jóvenes).

Para muchos animales el sentido del oído es capital para su supervivencia, ya que utilizan los sonidos para detectar peligros, a la depredación detectando las presas o para comunicación. La mayoría de fenómenos que se producen en la Tierra tienen asociados sonidos característicos: la lluvia, las olas"), el fuego, el viento, etc. Muchas especies, tanto mamíferos, anfibios como la rana o los pájaros, han desarrollado órganos "Órgano (anatomía)") especiales para la producción de sonidos, que en el caso de algunos pájaros ha evolucionado hasta el canto o hasta el habla humana. Los humanos incluso hemos desarrollado una cultura y una tecnología basada en la generación y la transmisión de sonidos (cultura de transmisión oral, teléfono, radio "Radio (medio de comunicación)"), fonógrafo, disco compacto, etc.).

Para la medida del sonido se utiliza una escala logarítmica,[5]​ que permite representar magnitudes muy grandes y muy pequeñas con números relativamente pequeños, y que es una cifra adimensional porque es una relación entre dos magnitudes con las mismas dimensiones, la presión sonora respecto de una presión sonora arbitraria de referencia que, por convenio internacional, son los 2 micropascales. Se trata de la escala de decibelios, que expresa la magnitud del sonido en decibelios, décima parte del belio, una unidad raramente utilizada. El origen de la escala, el valor 0, corresponde al umbral auditivo humano (2 μPa), de forma que los valores negativos corresponderían a sonidos imperceptibles por el hombre. El decibelio no es una unidad incluida en el Sistema Internacional de Unidades (hay científicos que no la consideran una unidad),[6]​ aun así es aceptado para utilizarse junto con las unidades del SI.[7]​.

sound pressure level

The sound pressure level or sound level is a logarithmic measure of the effective sound pressure of a mechanical wave with respect to a reference source. It is measured in decibels:

where p is the reference sound pressure (in air it is customary to consider µPa, and p is the value of the effective pressure that we want to measure.

If the propagation medium is air, the sound pressure level (SPL) is almost always expressed in decibels with respect to the reference pressure of 20 μPa, generally considered the threshold of audibility for human beings (approximately equivalent to the sound pressure produced by a mosquito flying three meters away). Measurements of audio equipment are almost always made in reference to this value. However, in other media, such as water, a reference pressure equal to μPa is often used.[8] In general, it is necessary to know the reference level when comparing SPL measurements and the fact that the unit dB (*SPL) is often abbreviated as dB can be misleading, since it is a relative measurement.

Considering the range of human perception (from 20 µPa to 20,000 Pa) on the decibel scale, perceptible sounds are between 0 and 180 decibels (dB) - The following table shows some examples:.

Sound intensity level

The sound intensity level or acoustic intensity level (L) is a logarithmic measurement of the sound intensity (measured in W/m²) compared to a reference value (10 W/m²). The relationship is defined as:[9]​.

where I is the sound intensity in W/m², and I is the reference value, which corresponds to the lowest sound intensity audible to the human ear at a frequency of 1000 Hz. The sound intensity level is a dimensionless value and is expressed in decibels (dB).

On the other hand, if instead of taking the threshold intensity at 1000 Hz, we take the real threshold intensity for each frequency, then we would talk about loudness and it would be expressed in phons,[9]​ the unit of measurement of the intensity of the sound sensation for the human ear.

The sensation that a sound produces in us is subjective and depends on the observer. There is no proportional relationship between the physical intensity of a sound and the sound sensation or loudness that it produces in us; the sound sensation approximately follows the Weber-Fechner law, which tells us that the sound sensation follows an arithmetic progression while the sound stimulus follows a geometric progression.[10]​.

Noise pollution or noise pollution is the excess of sound that alters the normal conditions of the environment in a certain area. Although noise does not accumulate, move or last over time like other pollution, it can also cause great damage to people's quality of life if it is not controlled well or adequately.

The term "noise pollution" refers to noise (understood as excessive and annoying sound), caused by human activities (traffic, industries, leisure venues, airplanes, ships, among others) that produces negative effects on the hearing, physical and mental health of living beings.

This term is closely related to noise because this occurs when noise is considered a pollutant, that is, an annoying sound that can produce harmful physiological effects such as decreased hearing ability or deafness and psychological effects for a person or group of people.

The World Health Organization (WHO) considers 70 dB (A) as the desirable upper limit. Different countries have health standards on acceptable limits both in the social environment and in the work environment, as well as measures to reduce noise pollution.

• - Acoustics.

• - Digital audio.

• - High-end audio.

• - Noise pollution.

• - Surround sound.

• - Silence (sound) "Silence (sound)").

• - Volume (sound) "Volume (sound)").

• - Buzz.

• - M. Crocker (editor), 1994. Encyclopedia of Acoustics (Interscience).

• - Farina, Angelo; Tronchin, Lamberto (2004). Advanced techniques for measuring and reproducing spatial sound properties of auditing. Proc. of International Symposium on Room Acoustics Design and Science (RADS), 11–13 April 2004, Kyoto, Japan. Article.

• - L. E. Kinsler, A. R. Frey, A. B. Coppens, and J. V. Sanders, 1999. Fundamentals of Acoustics, fourth edition (Wiley).

• - Philip M. Morse and K. Uno Ingard, 1986. Theoretical Acoustics (Princeton University Press). ISBN 0-691-08425-4.

• - Allan D. Pierce, 1989. Acoustics: An Introduction to its Physical Principles and Applications (Acoustical Society of America). ISBN 0-88318-612-8.

• - D. R. Raichel, 2006. The Science and Applications of Acoustics, second edition (Springer). eISBN 0-387-30089-9.

• - E. Skudrzyk, 1971. The Foundations of Acoustics: Basic Mathematics and Basic Acoustics (Springer).

• - Wikimedia Commons hosts a multimedia category on Sound.

• - Wiktionary has definitions and other information about sound.

• - Sound as vibration.

• - The Dictionary of the Royal Spanish Academy has a definition for sound.