Outside sound effects are picked up by a third microphone. In order to be certain that all the motley sounds die off at once, the volume in the last ten seconds is faded out by the engineer at the mixing panel. Mr. Sims, who is largely responsible for this excellent effect, conducted many experiments before he finally succeeded in adapting it to the studio. Studio engineer Ralph Davis and 'advisory director' Harold M. Sims. I have used a stop watch on fifty or sixty trains, actually timing the various units of the medley.
Trains sound different in hilly country from what they sound in flat country.
Even when you repeat the experiment at one point, there is a wide variation in every train, depending upon the atmosphere, the time of day, whether the train is going upgrade or down, whether it is picking up speed or slowing down, the length and weight of the train, its speed, power of the engine, and many other factors. Again, the time it takes a distant train to come up and pass one and disappear into the distance varies from three to five minutes. Limitations of the radio do not permit us nearly so much time, to say nothing of the fact that it would be tedious to listeners to wait that long. Three microphones are required for this illusion. What I really had to do was to build up a synthetic effect that would make the sound even more colorful than the real.