The brass tube length is about 0.61 meters. The duration of a cycle
in the waveform (after the initial impulse) is about 0.0035
seconds, so the speed of sound would be v = (d / t) = (2 x 0.61m) / (0.0035s) which is about 348 meters per second.
The settings for the synthesis using the echo.scm script are as follows:
delay length = 0.0035s
attenuation = 0.9
The waveform looks like: Sound