362 ChapTer 16 Location Sound techniques source to microphone from shot to shot; because the recordist is required to change lev- els in this situation, we'll get a shift in ambient sound and therefore a discrepancy in audio continuity. If the background noises shift from shot to shot, it creates a tough situation for an editor who is trying to invisibly cut two shots together to create the illusion of continu- ous time and space. For this reason we always record one minute of ambient sound (or room tone) at each and every location. After the director calls the last "Cut," before any- one starts striking the set, the mixer needs to ask everyone to be quiet for one minute of room tone. The mike is then opened at the normal, speech level and the boom operator announces the sound take by stating (1) the production title, (2) the location, (3) the date, and (4) announcing "one minute of room tone." Then everyone stands stock still while they record one minute of general ambient sound. After one minute, the mixer calls "End ambi- ence" and the set can be struck. It is important to do this while the crew and equipment are still on the set. Remember, they, too, were part of the ambient atmosphere during each take (the bodies absorb echoes, etc.). You must also do this even before turning off any movie lights, because they will make little pinging noises as the metal cools. This is a practice that people usually have very little patience for on a hectic film set, but it pays off big dividends in the editing room, because the editor can use this baseline ambience as a separate track to smoothly suture together shots with differing ambience (see Chapter 23). miscellaneous recording Challenges When directors scout a location, they are usually evalu- ating the visual qualities of the set, rather than its aural