It is often heard that "how many decibels does this noise exceed", "how many decibels is this volume", etc., to indicate the volume of the sound, what is the difference between "decibels" in the sound system?
Because humans have a very large range of hearing about volume, the energy difference between them can reach millions of times; coupled with the fact that the perception of human volume will become less and less sensitive as the volume becomes louder. Through the conversion of "decibels", such a huge number can be converted into tens to hundreds of values, which is not only convenient to present, but also more intuitive in the description of volume.
ratio
The most basic concept of decibels is the ratio, which must have a numeric value as a reference value to make a comparison. Assuming a marble's height of 1 cm is a reference value, Bob's height is 170 cm, and the ratio is 170; if compared with the tower (500 meters), the ratio is 50000.
decibel
A large ratio can be converted into a simpler number by decibel conversion. Also with the height of the marble 1 centimeter as a reference value, Bob's height is +22.3 dB, and the height of the tower is +46.9 dB.
The value is the same as the reference value, and the decibel value is equal to 0.
The value is smaller than the reference value, and the decibel value is less than 0.
The value is larger than the reference value, and the decibel value is greater than 0.
How loud is this sound? - Sound Pressure Level (SPL)
Describe sounds as "loud?" in our daily lives. Or "How many decibels does this sound?" It is the standard that uses "sound pressure level". In the sound pressure level, the "minimum sound pressure" that humans can hear is taken as the reference value (this volume is 0 decibels), so the volume of other sounds is greater than 0. Because we humans can't hear a smaller voice than this.
The unit used by the sound system – dBu
In professional sound systems, the signal value of 0.775V is used as the reference value; if the sound signal is between 0 and 0.775V, the decibel value will be "less than 0", and the sound signal will be "greater than 0" if the decibel value is greater than 0.775V. In the design of the general sound system, the maximum volume decibel value is about +18 ~ +24dBu, and more than that will produce broken tone and distortion.
The standard for digital signaling – dBFS
In the digital signal, as long as the volume exceeds the range of the value can be recorded, there will be a broken sound distortion situation, so in the digital signal, the "maximum and no distortion volume" as the reference value (that is, 0 dBFS), all sounds greater than 0 dBFS must be broken distortion sound, and the sound without distortion must be less than the reference value, and the decibel value will be "less than 0".
dBFS vs. dBu
The scale used in digital devices is a dBFS table, and values such as +4dBu are not visible. Since each device is designed differently, the volume of the output of a typical digital device +4dBu will be around -18 ~ -24dBFS.
Volume quasi-correction
When we connect many devices, in order to ensure the unity of the signal volume, we will use the frequency 1kHz volume + 4dBu sine wave to calibrate the volume between the devices, through the gain knob to compensate for the volume attenuation caused by the wire connection, so that the volume range of each device is set to be consistent, so as not to cause some devices have been close to the broken volume, the sound is still not added to the situation.
From theduet-music