I agree with Ken. The chinese whistles don't sound bad, on some engines even pretty good. But you rarely hear them because the enginemen mostly use the air horns.
And I've never quite understood the "code". And when they do use the whistles I have never heard an attempt to "play" (modulate) them. Whether air horn or whistle, everything seems to be one "bleep", and it's not quite clear for what reason. When a train gets ready to move you hear all kinds of "bleeps". "Bleep" set the brakes, "bleep" release, "bleep" highball, "bleep" get out of the way. "bleep" whatever....I've never figured out a pattern, although there undoubtedly is one.