Fig. 7. Wing movements during sound production recorded simultaneously with two different methods: high-speed video (top) and optical position detector (bottom). Four frames from one complete wing stroke are shown. Each frame is accompanied by an oscillogram of the sound (blue) and simultaneous trace of wing position vs time (red). Vertical broken lines (red) indicate the position of the scraper in the video frame. In the simultaneous sound and wing position traces, the vertical broken line indicates the time corresponding to the video frame. (A) Maximal opening of wings, just prior to engagement of file and scraper and beginning of sound production. (B) The scraper contacts the first teeth of the file and the first sound waves are generated. Note decrease in the slope of wing position (red trace) when the scraper contacts the first teeth (green broken arrow). (C) The scraper crossing the middle portion of the file, maximum amplitude of the song pulse, increasing slope of wing position trace. (D) The scraper contacts the last few teeth of the file and comes to rest with the end of the sound pulse.