Commonly used frequency units are kilohertz (kHz), megahertz (MHz), gigahertz (GHz) and so on.
There are sometimes many frequency components in the electric signal carrying information; Mark the position of all these components on the frequency axis, and express the size of each component in terms of power or voltage, which is the "spectrum" of the signal. The frequency range it occupies is called the frequency band range of the signal.
For example, in telephone communication, the frequency range of voice signal is 300 ~ 3400Hz；; In FM broadcasting, the frequency range of sound is 40 Hz ~ 15 kHz, and the frequency range of TV broadcast signal is 0 ~ 4.2 MHz.
For sound, people's hearing range is 20 Hz ~ 20Hz~20000Hz, below which it is called infrasound, and above which it is called ultrasound.
In the radio frequency division defined by the International Telecommunication Union:
Ultra low frequency (ULF): 3 ~ 30 kHz.
Low frequency (LF): 30 ~ 300 kHz.
Intermediate frequency (MF): 300 ~ 3000 kHz.
High frequency (HF): 3 ~ 30 MHz.
Very high frequency (VHF): 30 ~ 300 MHz.
UHF: 300 ~ 3000 MHz.
Ultra high frequency (SHF): 3 ~ 30 GHz.
Extremely high frequency (EHF): 30 ~ 300 Hz.
Baidu Encyclopedia-Hertz (frequency unit in the International System of Units)
Baidu Encyclopedia-Hertz (Physical Unit)