In recording the sound of the voice, of course, the problem of establishing criteria for determining the beginning or ending of an individual's activity is quite simple. As previously stated, we are limited by the threshold of the apparatus used to record sound, whether it is the human ear or an electronic recording device. Assuming, by objective test, that the individual's hearing is within the normal range and that he is demonstrably placed at a distance from the persons being observed, so that we can reasonably expect to hear at least when they are saying even if not always what, our criterion becomes one of the presence or absence of sound. To be used accurately, the criterion should state the conditions of observation, i.e., such factors as distance from the person, being outdoors or indoors, presence of background noise and the like, which may be limiting features. In the same way, when a tape or wire recorder is being used, the characteristics of the instrument should be given, as well as the location of the microphone and its capacity for picking up the voice at varying distances and intensities.