I use a computer speaker system with one speaker in the main station that plays station-type sounds (carts, dogs, people, etc.) and the other speaker in the water tower (engine yard and machine sounds). These are connected to an MP3 player.
I made a 300 second stereo loop in Audacity taking sound bites from the 'net back when you could easily download them. I split this into ten 30-second sections. When a train pulls into the station, it’s magnet retriggers a reed switch tied to the sound loop, beginning at any of the 10 segments at random. It will then play up to 300 seconds, then shut down, starting at that point in the loop. This keeps it from getting boring. Also, it doesn’t take 300 seconds for a train to go around the loop, so without this “random start” it would be the same sounds each time the train returns.
I got the MP3 player from Dave Bodner. It was his prototype and can do as many as 80 random start points (eight banks of 10).
We also have an MP3 player that plays “The Low Rider” (like 6 different versions) as well as other “War” and “Cheech and Chong” tracks in the station where the Low Rider train parks. The amp gets its power from the rails, so it only plays when the trains run, though the MP3 player loops continuously throughout the day until I turn it off or it runs out of charge.
Our barn has cow sounds and the stock car has sheep that get figgity traversing rough terrain…, or when the ranch hands approach. (We have some very attractive sheep and lonely ranch hands.)
Sometimes, the Jazz band plays in the town square (cassette player) and the singer sounds exactly like Aretha Franklin.
Finally, somewhere along the line I picked up a telegraph sound module. The telegraph message is the same as the one you would hear at Dizzyland in Anaheim.