Time Weighting of Sound Level Meter
In real life, there are many types of noise, including steady-state noise, transient noise, and impulse noise, etc., and time weighting is introduced for different noise measurements. Time weighting is actually the time averaging of the measurement signal. Usually, the time averaging feature includes four modes, namely "Fast" (Fast) file, "Slow" (Slow) file, "Impulse" (Impulse) file and "Peak Hold" (Peak) file.
(1) For continuous sound signals, the "fast" and "slow" files are usually used for weighting. The weighting time constant of the "fast" gear is 125ms, which is generally used to measure unstable noise and traffic noise with large fluctuations. The fast gear is close to the human ear's response to sound. The weighting time constant of the "slow" gear is 1000ms, which is generally used to measure steady-state noise, and the measured value is an effective value. For steady-state continuous sound signals, there is no significant difference between the two weighting methods. However, if the measured sound fluctuates greatly, the result obtained by weighting with "slow gear" is more stable due to the different length of weighting time. However, due to the long averaging time, there will be errors in peak and valley measurements. Therefore, in order to accurately understand the real-time changes of the signal, it is appropriate to use "fast" weighting (fast gear is close to the human ear's response to sound, and fast gear and A weighting should be used when measuring the background noise of the soundproof room).
(2) The time constant of the "pulse" file is 35ms, which is used to measure the pulse noise with a long duration, such as punch press, hammer, etc. The measured value is the maximum effective value. The time constant of "Peak Hold" is less than 20ms, which is used to measure short-duration pulse sounds, such as guns, cannons and explosions, and the measured value is the peak value, that is, the maximum value.
Time weighting is usually used in sound level meter measurement, and the time weighting is used in conjunction with the previous frequency weighting to make the measurement results reflect the subjective perception characteristics of the human ear to a certain extent. In addition, the sound level meter can be connected with an external filter and recorder to perform spectrum analysis on the noise.
