length of tube: 18 in. -- (1m/39in) = 0.46m

time between peaks: 0.0025 sec

speed of sound = 2(length)/time = 2(0.46m) / 0.0025 sec = 368 m/sec

frequency: F = 1/T = 1/(.0025 sec) = 400 Hz

Graph of actual sound wave:

Part 2: Creating a plot of the soundwave using Scheme and SND:

Scheme line used to create this plot: (map-chan (echo .0025 .4))