Reprint: The concept of sound decibel, DBSPL.DBFS

transferred from: https://www.cnblogs.com/wangguchangqing/p/5947659.htmlDecibel decibel

Decibel (db) is a logarithmic unit (logarithmic unit), which is different from many common units such as "M", "SEC" or "kilogram", and it is not directly used to describe the size or amount of a physical quantity, it represents the ratio of two physical quantities of the same unit. Decibel is often used to describe sound, such as more than 50dB of noise will affect people's sleep and rest, but the decibel is not only used to describe the sound, it is also used to describe other fields such as electronics, such as the attenuation of signal strength, SNR and so on.
As mentioned in the preceding decibel is the ratio of two physical quantities, the amount of the denominator is usually a standard reference value (reference value), the decibel is described as the physical amount of the molecule relative to the reference value of the size, the decibel calculation formula is as follows:

DB=10XLog(value/valueref)

which v a l u E r e f ">v< Span id= "mathjax-span-38" class= "Mi" >al u Eref V is the reference value. It is important to use decibels to represent the baseline value of the physical quantity, and the reference value is expressed in decibels as 0dB.

Describe the decibel of the sound

Decibel can describe a lot of physical quantities, this article mainly introduces the decibel to describe the sound of the signal strength.
There are many physical quantities used to describe the intensity of sound: sound pressure, power, the voltage that produces a sound signal, and the amount of different physical quantities used to represent the intensity of the sound, and the decibel they get is different.

DB (DBSPL)

The sound is essentially a wave that travels through the air and transmits the vibrations of the tympanic membrane to the human ear. So, the size of the sound is actually a reflection of the intensity of the vibration. As the vibration of the air will cause a strong change in atmospheric pressure, you can use the degree of pressure changes to describe the size of the sound, this is the "sound pressure (spl,sound pressure levels)" concept, the unit is PA. For example: The sound of a rifle firing 1 meters away is about 7000pa;10 meters away from the car, about 0.2Pa.
The use of sound pressure as a measure of the decibel is DBSPL, usually used to indicate the size of the DB multi-point refers to the DBSPL. The relationship between sound pressure and sound size can be expressed using the following formula

I = P 2 x03c1; " > I=p^2/ρ

v a l u e R e f " >
where I is the intensity of the sound; P is the sound pressure; & #x03C1; " > ρ ρ is air resistance, usually at room temperature, the air resistance is about 400. The
decibel calculation also requires a to select a specific sound pressure value as the "standard value" (0 db), which is fixed. The has this base value descendant into the formula above:

Wherein, p is the sound pressure measurement value;PReF is the standard value (0dBSPL). The standard value of the sound pressure chosen here is2x10^? 5Pa, (μPa) is the smallest sound the human ear can hear at the 1KHz frequency, roughly equivalent to the sound of a mosquito flying 3 meters away. To put the standard values in the above style:

DBFS

In the digital age more audio decibel representations are DBFS. The DBFS is called the decibels full scale, and the full decibel is the representation of the decibel value of the value audio.

The DBFS benchmark is not the smallest or the middle of a certain value, is the largest value! That is, 0dBFS is the maximum value a digital device can achieve, except the maximum value is negative.
As an example of a digital audio sample for 16-bit unsigned, the 16-bit unsigned maximum value is 65536, so the DBFS formula:

DBFS=20 Xlog 10 (sample/ 65536) DBFS

In this way, the smallest DBFS =20xlog (1/ 65536) = 96d bf s . This means that 16-bit unsigned audio has a dynamic range of 0 ~ -96dbfs.

Reprint: The concept of sound decibel, DBSPL.DBFS