At the start of a concert there is always a certain voltage in the air hitting the musicians for obvious reasons, but also the sound engineers and stage assistants. All is silent, but ready to produce music. Think of what would happen if the concert were to begin with the first piece and, after an instrumental intro, the singer started singing but there was no sound coming out from his microphone! We don't even want to think about it... The concert begins, and the sounds are all a bit raw. Onstage the musicians still need to settle into their "sound", the mixes that had been set up during soundcheck now need to be adjusted, and are requested to the stage engineer with quick gestures and glances from the stage. At the same time the front-of-house engineer is working hard at moulding and blending the sound that is being sent out into the hall. After the first few pieces have been played the atmosphere begins to relax as all these components even out, and the sound engineers can begin to enjoy the result of their efforts, still keeping a steady hand (and ear) on the sound parameters, depending on the pieces being played.
When the concert is over, we all go onstage and chat to the musicians and the other technicians, exchanging opinions and comments. All that's left to do is to dismantle and put everything away and, whilst the last spectators leave, we are already at work, because the night is no longer young, and it'll be a fair bit before we can plunge into bed to then wake up the next day, in another concert hall, in another city, doing it all over again.