Live sound gain staging has a second ceiling — feedback — that studio recording does not have

In a recording studio, the only upper limit on gain is distortion/clipping. In live sound, there is a second, often lower ceiling: feedback. Microphones that pick up the output of the loudspeakers they are feeding create a loop that, above a certain gain threshold, generates the loud, sustained squeal of acoustic feedback. This means a live engineer must leave headroom not just from clipping but also from the feedback threshold — an acoustic property that changes with the room, the PA position, and the directivity of each mic. Mid-show gain changes (rather than fader changes) are particularly risky because they also change monitor mixes and increase the chance of crossing the feedback threshold on a monitor wedge without the engineer being able to hear it from front-of-house.

Examples

A vocal mic has -6 dB of headroom before feedback on the monitor — a comfortable working margin. Increasing gain by 3 dB mid-show to chase a quiet singer immediately halves that margin, risking feedback on the wedge.

Assessment

A studio engineer tries applying their standard gain-staging approach to a live rock show. What critical constraint do they encounter that they didn’t in the studio, and how does it change their gain decisions?