Sound check
A soundcheck, simplified as sound check is an activity that takes place a couple of hours before a concert. The performer(s) and the sound crew run through a short song to make sure that the sound in the venue is clear and at the right volume and tonal frequencies. Soundchecks are especially important for popular and other musical genres that use heavily-amplified PA systems; having correct sound is very important to the success of such events.  A soundcheck remains part art and not all science, however, because the acoustics of a venue often change somewhat once it is filled with an audience.