3.1 The Unprocessed Waveform Data First, we made a high-resolution graphical plot of the waveform of this signal, at a scale of 5 in. per 1/10 sec, for detailed visual examination. The plot of the entire interval 22 63 comprises a roll of paper 12 in. wide by 234 ft long. Reductions of excerpts of this plot are reproduced in Fig. 4. In this figure and in the following discussion, time is noted in seconds from the beginning of the interval. The first region to be noted in Fig. 4 is the area around 131 sec. This region is typical of the high level of motorcycle noise that characterizes the first 2 minutes of the data. In the region of 132 to 133 sec, we can see the amplitude of the noise slowly drop. Later, when we discover the trajectory of the motorcycle as a by-product of detecting the sounds of shots, we find that the motorcycle was approaching the corner of Houston and Elm Sts. at this time. Therefore, this diminution of motorcycle noise is probably due to the slowing necessary to negotiate the 120(deg) left turn at the corner. At about 36.5 sec, we note a single large impulse of relatively long duration. Because of its length and because the region following this impulse is largely free of other impulses, such as the echoes normally associated with loud impulsive sounds, we feel that it is unlikely that this impulse represents the sound of gunfire. The regions around 137.3 to 138.7 and 139.2 to 140.9 sec are notable for a number of brief, loud impulses. These impulse patterns, the first to appear in the data up to this time, were judged as potentially representing gunfire. The region from 144.8 to 147.2 sec, which does not appear in Fig. 4, also contains a large number of impulses of similar character. Because this region is about twice as long as the 23 64 FIG. 4. WAVEFORMS RECORDED FROM CHANNEL 1 TRANSMITTER WITH STUCK MICROPHONE. 24 65 preceding ones. it was identified as possibly representing two separate impulse patterns, and, therefore, as potentially conraining the sounds of two shots.