Background noise, also known as “background noise”, generally refers to all interferences that have nothing to do with the presence or absence of signals in the generation, inspection, measurement or recording system. But in the measurement of industrial noise or environmental noise, it refers to the ambient noise outside the measured noise source.
Background noise. Generally, it refers to all interferences that have nothing to do with the presence or absence of signals in the occurrence, inspection, measurement or recording system. But in the measurement of industrial noise or environmental noise, it refers to the ambient noise outside the measured noise source. For example, if traffic noise is to be measured in the street near the factory, the factory noise is the background noise. If the purpose of the measurement is to measure the factory noise, the traffic noise becomes the background noise. In the process of noise measurement, attention must be paid to the interference degree of background noise.
Background noise can not affect people’s listening to the main voice, especially when it is necessary to be quiet. Music is not only a sound, but also a silent melody. At this time, it is important not to introduce a little noise, such as the rumble of electric fans and the noise of traffic. Noise evaluation curve (NC) is a common standard used to identify background noise.
However, it is not suitable for the evaluation of time-varying information only. When sound waves carry important information, such as a wonderful speech or a wonderful melody, there must be stricter standards.
In some cases, the quieter the better. If the background noise is reduced, other previously hidden noises may be highlighted. Background noise can be enhanced to the level of noise evaluation value without people’s awareness. This noise masking method is more economical than the noise control method.
It is necessary to establish special standards for venues where special events are held. For example, in the recording studio, the accuracy of the noise standard should reach the lowest noise level of the recording equipment, but it should be higher than the hearing threshold of the recorder. In this way, at the beginning of recording, the recorder can clearly distinguish the noise sources, and the noise will not be heard from the tape.
Influence of background noise
When the noise level of a noise source is measured at a certain site, the noise transmitted to the site by other noise sources (called background noise) is usually impossible to be excluded, but the overall measurement can only be carried out, which makes the sound level of the noise source to be measured produce a certain deviation. This is the effect of background noise.
If other noise sources can be excluded, the same problem does not exist, but for most occasions, the noise sources are not specific and there are many, so it is difficult to divide them.
然而，排除要测定的噪声源(所谓“象”噪声源)是比较容易的。首先停止对噪声源的发定，仅测定背景噪声的噪声级然后再测定对象噪声源和其他噪声源所构的复合噪声的声级。若背景噪声的强度比合噪声的强度低 10 分贝以上的话，那么由背景噪声所造成的影响将低于 1 分贝，即以视为无背景噪声的干扰。当两者之差小 10 分贝时，按对复合噪声的强度以修正后，可以求得对象噪声源的大概噪声级。
However, it is easy to exclude the noise source to be measured (so-called “image” noise source). Firstly, the determination of noise source is stopped, only the noise level of background noise is measured, and then the sound level of compound noise composed of object noise source and other noise sources is measured. If the intensity of the background noise is more than 10 dB lower than that of the combined noise, the influence caused by the background noise will be less than 1 dB, that is to say, it is regarded as the interference without background noise. When the difference between them is less than 10 dB, the approximate noise level of the object noise source can be obtained by correcting the intensity of the composite noise.