What's the difference between noise and sound？

Release time：2022-05-04    Click：34

Sound :　

    Sound is the vibration of air molecules. The vibration of an object (which we call the "sound source") causes the corresponding vibration of air molecules, which is transmitted to the human ear and causes the eardrum to vibrate, which is then passed through a series of auditory organs, such as the middle ear and the inner ear, to make the human being hear the sound.

    Throw a stone into the calm water, will form a group of water waves spread around, this is what we can see the more intuitive "wave", the air molecules vibrate to form sound waves.

    Air molecules vibrate to form sound waves to be a little more complex, it is from the source of sound to the surrounding three-dimensional diffusion of a set of dense waves, air molecules are not from the source of the sound has been running to your ears, but in its original position vibration, which caused with its neighbouring air molecules vibrate with it, the sound is so very quickly from the source of the outward propagation of the sound, sound propagation speed in the air is 331 metres / second.

Frequency of sound 　　

    The number of vibrations of sound waves per second is called the frequency, the frequency of 20Hz ~ 20KHz is called sound waves; frequency greater than 20khz is called ultrasound;

    Frequency less than 20hz called infrasound. Ultrasound and infrasound can not be heard by the human ear, earthquake waves and tsunamis are infrasound. Some animals have much more sensitive ears than humans, for example, bats can "hear" ultrasound.

    The world rarely exists in a single frequency "pure sound", we hear the sound is mostly a variety of frequencies of the composite sound, such as musical instruments issued by a single tone is a periodic composite sound, speech is a non-periodic composite sound. 

    Let us have a more intuitive concept of the frequency of the sound: the drum "pong pong" sound frequency is very low, about 35Hz-7kHz; human voice frequency range is mainly in the 200 Hz to 4000 Hz between; gongs, bells, the frequency of about 2000 Hz to 3000 Hz or so; in the human voice, the female voice than the frequency of the male voice to be a little bit higher; children's voices than the frequency of the adult a little bit higher; The frequency of "ah-ah" sounds is lower, "ee-ee" sounds are slightly higher, and "snorting and hissing" sounds are the highest. This is useful to know and can often be used in practice to test the patient's

In practice, it can often be used to test a patient's response to sound frequencies before and after wearing a hearing aid.

   High and low frequencies are relative. In the speech range, the area above 1000 Hz is usually referred to as the high-frequency zone, the area between 500 Hz and 1000 Hz as the mid-frequency zone, and the area below 500 Hz as the low-frequency zone.

Noise :

　　1. From the point of view of subjective needs : All unwanted sounds can be called noise. For example, in the silence of the examination room, the music is also noise; when you watch TV, other people's conversation is noise; when you talk with others, the TV sound becomes noise. 

　　2. From the point of view of physical analysis: all irregular or random acoustic or electrical signals can be called noise.

   　 The size of the sound is the sound intensity or sound pressure, which is the sign of the size of the sound energy. In general, the sound pressure is large, we hear the sound is also loud. Shouting or speaking with force also makes the sound louder. In addition to the professional use of pressure and energy units to measure the size of the sound, usually use a relative value of decibels (dB) to mark. For example: the normal hearing of a young person is zero decibels (hearing level), the sound of the environment in the dead of night is about 20 decibels (sound pressure level of the same below), the sound of a normal conversation between two people is about 60 decibels, and the output of a high-powered hearing aid can reach up to 140 decibels.

　　The height of the sound is the frequency of the sound, with the number of vibrations per second to measure, the unit is Hertz (HZ). The human ear can hear a wide range of sounds from 20-20,000 Hz. It is customary to refer to sounds below 500 Hz as low-frequency sounds. For example, the sound of knocking on the door. 1000 to 2000 Hz sound is called the middle frequency sound, more than 2000 sound is called high frequency sound. 500, 1000, 2000 Hz is the main frequency of people's verbal communication, so it is called the language frequency. They are the most commonly used to determine the degree of hearing loss.

　　The characteristic of sound is timbre. In life, it is easy to tell the difference between the sound of a piano and the sound of a trumpet, even though they are sounding the same pitch at the same loudness. This is because the sounds in the environment are composite sounds (including speech sounds), and there are many peripheral sounds mixed around a major frequency tone, and the strengths and weaknesses of these components make up the different timbres.