Audio
Gain Before Feedback (GBF)
01 — Definition
The maximum system gain you can take before a microphone-to-speaker loop starts to ring. It climbs when you shorten the mic-to-source distance, use directional mics aimed away from the speakers, notch out the ringing frequencies, and reduce the number of open mics (each doubling of open mics costs about 3 dB). It is the practical ceiling on how loud a live mic can go.
02 — In the field
Every doubling of the open-mic count costs you about 3 dB of gain before feedback, so going from four mics to five costs around 1 dB, not 3. Mute unused channels and gate where practical: closing four idle mics can buy you 6 dB of clean headroom.