Interpretation of A/C Weighting in Sound Level Meter and Noise Meter
The sound level meter, also known as the noise meter, is the most basic noise measuring instrument. It is an electronic instrument, but it is different from objective electronic instruments such as voltmeters. When converting an acoustic signal into an electrical signal, it can simulate the time characteristics of the human ear's response speed to sound waves; the frequency characteristics of different sensitivities to high and low frequencies and the intensity characteristics of changing the frequency characteristics at different loudness. Therefore, the sound level meter is a subjective electronic instrument.
Signal-to-noise ratio: Signal-to-noise ratio (Signal NoiseRatio) is referred to as signal-to-noise ratio or signal-to-noise ratio. The ratio between them, usually expressed in "SNR" or "S/N", generally in decibels (dB), the higher the signal-to-noise ratio, the better.)
For example: We know that when the radio is listening to the radio or the tape recorder is playing music, the speakers always contain various noises in addition to the radio and music. Some of these noises are interference generated by lightning, motors, electrical equipment, etc.; some are generated by the components and devices of the electrical equipment itself. All these noises we call noise. With less noise, radio and music will sound clearer. In order to measure the quality of electro-acoustic equipment, the technical index of "signal-to-noise ratio" is commonly used. The so-called signal-to-noise ratio refers to the ratio of the useful signal power S to the noise power N, denoted as S/N.
Weighting (weighting): Weighting (Weighted) is also called weighting or hearing compensation, which has two meanings: one is to consider the different conditions of the equipment during normal use and measurement, and the artificial correction added to the measured value is called weighting . Or it can be understood as: a correction factor added to the measurement to correctly reflect the measured object (this is also a standard set by the country for the purpose of unifying noise measurement). For example, when measuring noise, since the human ear has the highest sensitivity to 1-5kHz and is not sensitive to low-frequency components, when evaluating the noise from the auditory sense, each part of the audio frequency spectrum must be weighted, that is, it needs to be used when measuring noise. Through a filter equivalent to the auditory frequency characteristics, to reflect the sharp sensitivity of the human ear 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 level. At present, the weighting curve A is commonly used, and dBA is used to express the measured value of this A weighting.
Frequency weighting (weighting network): In order to simulate the different sensitivities of human hearing at different frequencies, there is a built-in auditory characteristic that can simulate the human ear, and correct the electrical signal to a network similar to the hearing. called a weighted network. The sound pressure level measured through the weighting network is no longer the sound pressure level of the objective physical quantity (called linear sound pressure level), but the sound pressure level corrected by the sense of hearing, called the weighted sound level or noise level.
There are generally three types of weighting networks: A, B, and C. The A-weighted sound level is to simulate the frequency characteristics of the human ear to low-intensity noise below 55 decibels; the B-weighted sound level is to simulate the frequency characteristics of moderate-intensity noise between 55 and 85 decibels; the C-weighted sound level is to simulate the frequency characteristics of high-intensity noise characteristic. The difference between the three is the degree of attenuation of the low-frequency components of the noise. A attenuates the most, followed by B, and C the least. The A-weighted sound level is the most widely used in noise measurement in the world because its characteristic curve is close to the hearing characteristics of the human ear, and B and C are gradually used.
Time weighting (meter sensitivity): slow, fast, pulse or pulse hold, peak hold
