Gain before feedback (GBF) is the maximum amount of amplification you can apply to a microphone in a given environment before it starts to feed back. Maximum GBF means you can make vocals heard over loud bands, monitors loud enough for the singer to hear themselves on stage, and PA systems that fill rooms without distorting. Insufficient GBF means quiet vocals, frustrated musicians, and uncontrollable squealing. This guide covers the techniques that maximize GBF in any room.
Why feedback happens. A microphone picks up the sound from a speaker, which is then amplified back through the speaker, which the microphone picks up again, in an exponential loop. The frequency that feeds back first is whichever frequency the room/PA/mic combination amplifies most. Reducing the amplification of that specific frequency moves the feedback ceiling higher.
Microphone choice and placement. Cardioid mics reject sound from behind; supercardioid mics reject sound from the sides. For monitor wedges in front of the singer, supercardioid is usually better (rejects the wedge sound directly behind the mic). For wedges to the side of the singer, cardioid is usually better (rejects the wedge sound to the side). Match the mic pattern to the monitor position.
Mic distance matters. The closer the singer is to the microphone, the more GBF you have. A singer 2 inches from the mic has 12+ dB more GBF than the same singer 12 inches away. This is just the inverse-square law working in your favor. Every singer should be coached to "eat the mic" for maximum GBF.
Speaker placement vs microphone placement. The dead spot of a cardioid mic (180 degrees behind the capsule) should point directly at the loudest speaker (usually the monitor wedge or main PA). The on-axis pickup (0 degrees in front of the capsule) should point at the singer. These two angles, set correctly, dramatically reduce feedback before any EQ is applied.
Ringing out monitors. With the band off the stage and only a single mic open, slowly raise the monitor wedge fader until you hear the room start to ring (the building tone before full feedback). Identify the frequency by ear — over time you will get good at this. Notch that frequency by 6 to 12 dB on the monitor send's graphic EQ. Push the fader up further. The next ringing frequency will appear. Notch it. Repeat until the monitor is loud enough for the singer.
A typical wedge will need 3 to 6 EQ notches to be ringable to usable level. Common notch frequencies: 250 Hz (room boom), 500 Hz (boxiness), 1 kHz (vocal honkiness), 2 kHz (vocal harshness), 4 kHz (snare/hi-hat bleed), 8 kHz (cymbal brightness). Each room is different — this list is a starting point for ear training.
Feedback identification by ear. Train yourself to recognize specific frequencies by their character. 250 Hz feedback sounds boomy. 500 Hz sounds boxy. 1 kHz sounds nasal. 2 kHz sounds honky. 4 kHz sounds piercing. 8 kHz sounds whistling. With a year of live mixing, you can identify the feedback frequency within 1 second of hearing it start. This is the core skill that separates beginner from intermediate live engineers.
High-pass filters before EQ. Every vocal mic should be high-passed at 120 to 150 Hz. Every drum mic except kick should be high-passed at 100 to 250 Hz. Removing low-frequency content that the mic does not need to capture removes a major source of feedback potential. The high-pass alone can buy you 3 to 6 dB of GBF.
In-ear monitoring eliminates monitor feedback entirely. There are no wedge speakers on stage, so there is no monitor-to-mic feedback loop. The only remaining feedback risk is the FOH PA, which is much further from the stage and easier to manage. This is why every modern touring act uses in-ears.
Stage volume affects FOH GBF. If the band's on-stage instrument volume is loud (loud guitar amps, acoustic drums in a small room), the bleed into the vocal mics increases. The bleed pushes the vocal mics closer to feedback even before you turn them up. Reducing stage volume — quieter guitar amps, electronic drums, in-ears — reduces bleed and increases the GBF available for FOH.
Common mistakes: pushing monitor levels before ringing out (instant feedback), forgetting to high-pass mics (low-end mud and reduced GBF), using cardioid mics with wedges directly behind the singer (wrong rejection pattern), trying to fix feedback with the master fader instead of identifying the specific frequency, ignoring stage volume (the root cause of bleed-induced feedback), notching too narrowly (the frequency drifts as the room fills with people).