Well, John for the train approaching the crossing, there is no need to repeat this sound over and over again since the electronics in my conceptual audio system should know exactly where the train is and where the headphone wearer is at all times. I envision a system of position detection based upon wireless GPS technology which can track the whereabouts of objects on the layout as well as human headset wearers.
The entire train building would be the GLOBAL aspect of my scaled-down global positioning system. Various "satellites", electronics devices, mimicking real-world GPS satellites, positioned stationary, inside the building would function similar to real-world GPS satellites orbiting the earth. My same "hobby scale GPS system" would also navigate the scale-model autonomous trains and road vehicles according to strict schedules on my conceptual futuristic layout as well. I want to eliminate as much physical sensors and hardwiring as possible. Boy, I am thinking well outside the hobby technology box here.
Yes, it would take some smart person to invent what I alluding to here. I supposed the sound system in Trainz is triggered too. If my Trainz free-roaming camera is parked at a RR crossing, I will hear the train approach and leave following the doppler effect. This sound sequence will only occur once and not repeatedly after the train passes and is gone. If the headphone wearer is physically walking around the train layout and following the train's movements, he might hear a steady locomotive sound in that case unless the engine is changing speed in which case the headset wearer might hear air brakes, engine revving, turbocharger whine, coupler slack noise, etc. What I am alluding to is situational: how the layout is behaving with respect to headset wearers standing nearby.
Now, another object like a barking dog, could repeat occasionally as long as the headset wearer is standing near it and hasn't moved to another part of the layout.
And certainly, real train recordings could be used but I also thought of computer-generated synthesized sounds as well as on a music keyboard or a Moog synthesizer.
How realistic can a synthesized engine sound be made?