-3db, half Power point and pass band a little understanding of the hardware knowledge

For low pass frequency response, the signal amplitude will begin to decay as the frequency of the signal increases to a certain extent. When the power of the signal decays to the original half of the time there are:

The corresponding -3db position on the axis is called "Half power Point", if the signal amplitude (i.e. voltage) is measured, because the power and voltage is the square relation, so the signal amplitude attenuation is 0.707 times times of the original time that is half power point

Usually the -3db position is the cut-off frequency of the pass band, or the dividing between the band and the band. For the flatness of the band and the attenuation amplitude of the band, different types of filters have different performances.