The master output feeds the main PA at a level controlled by the venue; the booth output is a separate signal at an independently adjustable level sent to the DJ's monitor speaker.
The master output is the main stereo signal sent from the mixer to the venue's PA amplification system, typically controlled in level by a house engineer or by the master volume knob. The booth output is a discrete, independently level-controlled signal routed to the speaker or speakers behind the DJ position, allowing the DJ to adjust monitoring volume without affecting what the room hears.
Why it matters
Separating the two signals means a DJ can raise or lower their booth monitor to hear the mix clearly without accidentally changing the front-of-house volume, which protects the audience experience and the venue's gain structure. This independence is essential in loud club environments where stage wash from the main PA is insufficient or too delayed for accurate monitoring.
In practice
Set the booth level before the set starts: play a track at a representative level in the cue mix, bring the booth up until you can clearly hear detail without fatigue, and leave it there. Avoid chasing the booth level up during the set as the room fills and absorbs more sound; that is the engineer's domain on the master side.
