Lower and upper frequencies are also called

Concept:

• Frequency points ƒL (fc1) and ƒH (fc2) relate to the lower corner or cut-off frequency and the upper corner or cut-off frequency points respectively were the circuits gain falls off at high and low frequencies.
• These points on a frequency response curve are known commonly as the -3dB (decibel) points. So the bandwidth is simply given as:
• Bandwidth, (BW) = fH - fL
• We see from the curve given above that at the two corner or cut-off frequency points, the output drops from 0 dB to -3 dB and continues to fall at a fixed rate. This fall or reduction in gain is known commonly as the roll-off region of the frequency response curve.
• These -3 dB corner frequency points define the frequency at which the output gain is reduced to 70.71% of its maximum value. Then we can correctly say that the -3 dB point is also the frequency at which the systems gain has reduced to 0.707 of its maximum value.

- 3 dB = 20 log10 (0.7071)