The sound level is the volume at which a recorded effect, or signal from a microphone or other source is at when it comes out of the speakers. There are often a series of faders that the signal has to pass before coming out of the other end of the sound desk - these all affect the eventual level of the sound.

The level on a fader is normally marked between -infinity, and +10 dB - on a logarithmic scale. If the fader is at 0 dB, then the signal will not be changed. If the fader is higher than 0, then the signal will be boosted, and if the fader is lower than 0, it will be decreased.

The dB change is additive - so, if a signal goes through one fader which modifies it by -10dB, and then through the master fader which modifies it by -10dB, then that is the same as going through the first at -20dB, and the master at 0dB. (This may seem logical, but don't forget that on the physical fader, the distance between 0db and -20db is less than twice the distance between 0db and -10db)

If you're after any other theatre tech information, then do take a look at 'Everything you ever wanted to know about theatre tech, but were afraid to ask'