Recognizing sound
Why can’t astronauts hear each other even when they are face to face in space? Why can we tell who is speaking by their voice? How loud a sound can cause hearing damage? Is a hearing aid a loudspeaker? What is the “banana chart”? You will know after reading it.
What is sound?
Scientists have given the definition of sound: sound is the vibration of objects produced by sound waves, through the medium (air or solid, liquid) and can be perceived by the human or animal hearing organs fluctuations.
From the definition of sound, we know that there are three key points: the first is vibration to produce sound, for example, when beating a drum, if we do not want to continue to produce, we put our hands on the drum surface, not to let the drum surface continue to vibrate; the second is that there must be a propagation medium, such as space astronauts face to face also have to use the walkie-talkie is the reason that there is no air in space lack of medium; the third is perception, if the function of the perceptual organs have deficiency, you will not be able to hear the sound.
The three elements of sound.
To scientifically describe the appearance of a sound, three elements are needed: frequency, loudness, and timbre.
1. Frequency: Since sound is produced by vibration, it has a frequency, which is the number of vibrations in one second.
The unit of frequency is Hertz. Nature exists in the sound from 1 Hz, to hundreds of thousands of hertz, the range spans a huge range, but the human ear can hear is limited, from 20 Hz to 20,000 Hz. Within the range that the human ear can hear, the frequency level is sometimes commonly referred to as the pitch level, with high frequency being high, and soprano’s frequency can reach 1200 Hz.
And in the range of 20-20,000 Hz, it is divided into: the low frequency tone below 200 Hz, the middle frequency tone from 200-6000 Hz, and the high frequency tone above 6000 Hz. Among them, the middle frequency band is the most important frequency band in the natural sound, and is also the frequency band where the human ear is most sensitive to hearing, and we usually talk about hearing aid fitting, which is also the first thing to ensure that the hearing in the middle frequency band is well compensated.
2.Loudness: the strength of the sound.
Loudness is mainly dependent on the sound intensity, but also related to the frequency of the sound. People for the subjective feeling of strength is called loudness, the unit of measurement for decibels (Db), which is based on the sound pressure ratio of 1000Hz sound at different intensities, taking its common logarithmic value of 1 / 10 depending.
For 1000Hz sound signal, the human ear can feel the lowest sound pressure of 2x10E-5Pa, this sound pressure level as 0dB, when the sound pressure exceeds 130dB human ear will not be able to tolerate, so the dynamic range of human ear hearing 0 ~ 130dB.
The sound loudness of common occasions.
0 decibels: 10 feet (about 3 meters) outside a mosquito in flight
10 decibels: very quiet room
13 dB: the buzzing of a light bulb
20 dB: A country night
30 decibels: a night in the desert
40-60 decibels: the sound of a normal conversation
50-53 decibels: the sound of a working washing machine
60-80 db: A car passing 10 meters away
70 decibels: a vacuum cleaner at 10 feet (about 3 meters); the maximum noise that humans can tolerate (without hearing loss, sleep disorders, anxiety, learning disabilities, etc.) as determined by the U.S. Environmental Protection Agency
85 decibels: long-term effects can cause hearing damage
90 decibels: a bus or truck passing 10 feet (about 3 meters) away; a food mixer
100 decibels: the maximum volume of general household audio equipment
104-107 dB: sounds that begin to cause pain (at 2750 Hz)
110-140 decibels: jet aircraft engine at 100 meters away
116 decibels: sound that the human body begins to feel vibrations (at low frequencies)
120-130 dB: the front row of a rock concert
127 dB: sound that starts to cause ringing in the ears
128 decibels: the largest human scream measured from 8.2 feet (about 2.5 meters) away
140 decibels: even if the sound is very short, it can cause hearing damage
192.8-194.7 decibels: the maximum intensity of sound that can theoretically be transmitted by the Earth’s atmospheric pressure
The human ear’s perception of sound is not only related to sound pressure, but also to frequency. Sound pressure level is the same, the frequency of different sounds, sound loudness is also different. For example, an air compressor and a chainsaw, with the same sound pressure level of 100 decibels, will sound much louder than a chainsaw.
In our hearing test and hearing aid fitting process, the testers will choose a certain loudness of sound in the frequency band of 125, 250, 500, 1000, 2000, 4000, 8000, etc. and test how many decibels the patient can hear respectively. The hearing test is not exactly the same as the vision test. For the vision test, the tester will tell us how many degrees in the left eye, how many degrees in the right eye, and whether there is astigmatism. A hearing test, on the other hand, is how much loss of XX Hz, and the loss may be different for different frequencies. For example, the hearing loss in the frequency band of 1000 Hz is 50 decibels, meaning that the sound of 1000 Hz, loudness below 50 decibels he can not hear.
The normal hearing test will show that each frequency point is within a range, and this range is eventually reflected in the table, which is often called “banana chart”. If there is a hearing loss, some monitoring points will not be in the “banana chart”. Hearing aid fitting is to compensate for the loss in different frequencies, so that when the hearing aid is worn again, the monitoring points will be within the “banana chart”.
The subjective sound perception of the human ear is based on the sound pressure and frequency, and is called the loudness level in squares. The processor of a hearing aid or cochlear implant is programmed to analyze the user’s environment from this point of view, and if it is a noisy environment, there can be some noise reduction processing, etc. In the current hearing aids and cochlear implants, there are already applications of such programs.
3. Timbre: the characteristics of the sound.
Even at the same frequency and loudness, it can be distinguished as being from a different instrument or human voice. The difference in timbre depends on the different overtones. For each instrument, for different people, and for all objects that can make sound, there are many overtones of different frequencies that accompany the sound, in addition to a fundamental tone, and it is these overtones that determine its different timbre and allow the person to recognize that it is a different object or a different person that makes the sound. The different timbres give the sound a variety of charm.