This Esspee whistle on this GP9 is what a classic American train whistle should...

sound like.

It is a diminished chord (or possibly a diminished 7th) like many a classic steam locomotive. It is dark, exciting and spooky just like I love and have known since early boyhood. My other favorite whistle sound is a sad minor chord which was common on many classic GM/EMD engines of old. The whistles on modern-era d/e engines don't sound right to me. I grew up in the SF bay Area and SP GM/EMD classic whistles and rolling stock is what is near and dear to my heart.

Some old GM/EMDs, as the SD40 series, have a bright major chord but that still sounds sweeter than the new-age whistles on BNSF and UP engines of today. There is also a classic Pacific class steam engine at Niles Canyon, California.

That eerie whistle is a Leslie S5T according to this video, I don't know my whistle brand names but I know what sounds sweet to my ears:

https://www.youtube.com/watch?v=-HPBBffIsjM

If all breakfast cereals tasted and looked exactly the same it would be quite boring ... There are many, many different train horns in the world, that are equally pleasant to listen to, so you can learn how to widen your horizon of thinking ... Some horn collectors have many dozens, and try to collect them all, for horn honk conventions ... Some collectors repair and remanufacture ones that are hard to find or no longer exist ... There are steam whistle and bell collectors also

https://www.youtube.com/watch?v=PLzHwbfeAUg

You might find this website interesting as it gives the tuning as well as the history behind the horns.

Using a music keyboard like on a piano or digital piano, you can actually "play" the hornsounds as well as listen to them if there's a link provided. Press the notes as given. Like F-sharp, C-sharp, G, D, E, etc.

http://atsf.railfan.net/airhorns/index.html

I have been in SF Bay Area all my life. San Francisco, Brisbane, South San Francisco, Burlingame, San Mateo, San Carlos, Menlo Park, Redwood City, Mountain View, Sunnyvale, Santa Clara, San Jose, Fremont, and even Santa Cruz. I sure do miss the sounds of the ol' Espee, with the sweet diesel smells of the past.

Man I wish I was around for those nonstop Western Pacific Nathan M5’s and Northern Pacific P3’s. Oh so badly are those classics dearly missed.