14. Decibel as absolute unit

Although decibel is a relative unit that generally involves two values, it is also used as an absolute value by pre-setting reference value as 0dB as shown in the following tabel.

Symbol	Standard of 0dB	Explanation
dBm	0.775V	It is a unit based on voltage when there is electric power of 1mW in the 600Ω impedance which is used in telephone line.
dBu	0.775V	This unit (dBu) is an RMS measurement of voltage which uses as its reference 0.775 VRMS.
dBV	1V	1V is set as reference value regardless of impedance. V of dBV is shown in capital letter.
dBＷ	1W	1W is set as reference value.
dBSPL	Pascal	It is the decibel display of sound pressure level (SPL :Sound Pressure Level). of 0dBSPL is the minimum sound pressure level of 1kHz sound frequency that can be heard by the human ear.
dBi	Gain of Isotropic antenna	It is the gain of antenna based on virtual antenna (isotropic antenna) that evenly radiates electro-magnetic waves in all directions. It is also called absolute gain. The representation of dBi is only 2.15 larger when compared to dBd representation based on the dipole antenna. That is, it forms .
dBμ	1μVrms	It is a unit of electrical field intensity when the standard antenna of 1m height considers the radio field intensity which detects the voltage as 0dB. It is mainly used in the telecommunications field.