The most fundamental noise measuring tool is a sound level meter, commonly referred to as a noise meter. Although it is an electronic instrument, it is not the same as voltmeters or other more objective electronic instruments. It is possible to simulate the time characteristic of the human ear's response time to sound waves, the frequency characteristic with different sensitivity to high and low frequencies, and the intensity characteristic of changing the frequency characteristic at different loudnesses when an acoustic signal is converted into an electrical signal. As a result, the sound level meter is a flexible electrical device.
Signal-to-noise ratio: Also known as signal-to-noise ratio (Signal NoiseRatio), this term describes the proportion of useful signal power to unimportant noise power (the ratio of the maximum undistorted sound signal strength generated by the audio source and the noise strength emitted at the same time). The higher the signal-to-noise ratio, usually stated in "SNR" or "S/N" and normally measured in decibels (dB), the better.)
For instance, we are aware that when a radio or tape recorder plays music, other sounds are always present in the speakers in addition to the radio and music sounds. Some of these noises are interference produced by lightning, motors, electrical equipment, etc., while others are produced by the electrical equipment's own parts and mechanisms. We refer to all of these sounds as noise. The radio and music will sound clearer the less noise there is. The technical indicator "signal-to-noise ratio" is frequently used to assess the caliber of electro-acoustic apparatus. The useable signal power S to the noise power N ratio, abbreviated as S/N, is known as the signal-to-noise ratio.
Weighted (Weighted): Weighted is also called weighted or listening compensation. . Or it can be understood as: a correction coefficient added in the measurement to correctly reflect the measured object (this is also a standard set by the country for unifying noise measurement). For example, when measuring noise, since the human ear has the highest sensitivity to 1-5 kHz and is not sensitive to low-frequency components, when evaluating the size of noise auditorily, each part of the audio frequency spectrum must be weighted, that is, when measuring noise, it is necessary to make it Through a filter equivalent to the auditory frequency characteristics, to reflect the human ear's sharp sensitivity around 3000Hz and the poor sensitivity at 60Hz, this is weighting. Since the frequency response of the human ear varies with the loudness of the sound, different weighting curves are used for sounds of different loudness or sound pressure levels. Currently, a weighted curve A is commonly used, and dBA is used to represent this A-weighted measurement.
Frequency weighting (weighting network): In order to simulate the different sensitivities of human hearing at different frequencies, there is a network that can simulate the auditory characteristics of the human ear and correct the electrical signal to be similar to the hearing. It's called a weighted network. The sound pressure level measured by the weighting network is no longer the sound pressure level of the objective physical quantity (called the linear sound pressure level), but the sound pressure level corrected by the sense of hearing, which is called the weighted sound level or the noise level.
There are generally three types of weighted networks: A, B, and C. A-weighted sound level is to simulate the frequency characteristics of the human ear to low-intensity noise below 55 decibels; B-weighted sound level is to simulate the frequency characteristics of medium-intensity noise of 55 to 85 decibels; C-weighted sound level is to simulate high-intensity noise. characteristic. The difference between the three is the attenuation of the low-frequency components of the noise. A attenuates the most, B is the second, and C is the least. A-weighted sound level is the most widely used noise measurement in the world because its characteristic curve is close to the hearing characteristics of the human ear. B and C are gradually not used.
