You can replace the sounds in a Digitrax SFX or Soundbug decoder with a PR2 or PR3 programmer. There is a "Traction" sound project available on the Digitrax site. I've put that into an SFX 0416 decoder for one of my trolleys. The sound is OK, but I really wish these things had more volume available. I crank them up all the way, and I can only hear the engine sounds when the room is quiet and no other trains are running.
These are sound-only decoders, by the way.
It takes an iron man to play with a toy iron horse.
With ESU loksound decoders you need the programmer. Then you can change the sound to your own.
Wolfgang
Pueblo & Salt Lake RR
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What kind of decoder do you have?? Some allow a choice of bells and whistles/horns by setting certain CV's. MRC's sound-only "Sounder" also offers 4 different prime mover options (F-unit, Alco, SD-60 and SD-70 IIRC). Other sound decoders come pre-set with only one horn or whistle sound. A few now offer the option to download additional sounds from a website to change the sounds you have.
That depends on which decoder you have. Many of them cannot be changed other than adjusting the volume. If you mean you want to select a different prime mover, horn, bell, or other sound, that may be impossible.