The meaning of weighted weighting for noise level meters
Signal Noise Ratio (SNR)
It refers to the ratio of useful signal power to useless noise power. Usually measured by beta. Because power is a function of current and voltage, the signal-to-noise ratio can also be calculated using voltage values, which is the ratio of signal level to noise level. However, the calculation formula is slightly different. Calculate signal-to-noise ratio based on power ratio: S/N=10 log Calculate signal-to-noise ratio based on voltage: S/N=10 log Due to the logarithmic relationship between signal-to-noise ratio and power or voltage, to increase the signal-to-noise ratio, it is necessary to significantly increase the ratio of output value to noise value. For example, when the signal-to-noise ratio is 100dB, the output voltage is 10000 times the noise voltage. For electronic circuits, this is not an easy task.
If an amplifier has a high signal-to-noise ratio, it means a peaceful north view. Due to the low noise level, many weak sound details masked by noise will appear, increasing floating sound, enhancing air sense, and expanding dynamic range. There is no strict discrimination data to determine whether the signal-to-noise ratio of an amplifier is good or bad. Generally speaking, it is better to be around 85dB or above. If it is below the threshold, it is possible to hear obvious noise in music gaps under certain high volume listening situations. In addition to signal-to-noise ratio, the concept of noise level can also be used to measure the noise level of an amplifier. This is actually a signal-to-noise ratio value calculated using voltage, but the denominator is a fixed number: 0.775V, and the numerator is the noise voltage. Therefore, the noise level and signal-to-noise ratio are: the former is an absolute number, and the latter is a relative number.
After the specification sheet data in the product manual, there is often an A word, which means A-weight, that is, A-weighting. Weighting refers to modifying a certain value according to certain rules. Due to the sensitivity of the human ear to intermediate frequency objects, if the signal-to-noise ratio in the intermediate frequency band of an amplifier is large enough, even if the signal-to-noise ratio is slightly lower than that in the low and high frequency bands, it is not easy for the human ear to detect. It can be seen that if the weighting method is used to measure the signal-to-noise ratio, its value will definitely be higher than if the weighting method is not used. In terms of A weighting, its value is relatively high without considering the weight.
In addition, in order to simulate the different sensitivities of human auditory perception at different frequencies, a network is installed in the sound level meter that can simulate the auditory characteristics of the human ear and correct electrical signals to approximate the auditory sensation. This network is called a weighted network. The sound pressure level measured through a weighted network is no longer an objective physical quantity sound pressure level (called linear sound pressure level), but a sound pressure level corrected by auditory perception, called weighted sound level or noise level.
There are generally three types of weighting networks: A, B, and C. A-weighted sound level simulates the frequency characteristics of low intensity noise below 55dB in the human ear, B-weighted sound level simulates the frequency characteristics of medium intensity noise from 55dB to 85dB, and C-weighted sound level simulates the frequency characteristics of high-intensity noise. The main difference among the three is the degree of attenuation of the low-frequency components of noise, with A having the most attenuation, followed by B, and C having the least. Due to its characteristic curve close to the auditory properties of the human ear, A-weighted sound level is currently the most widely used type of noise measurement in the world, with B and C gradually being discontinued.
