For newbies to Sound Files and those who were not downloading sound files after PS3 engines arrived, your answer can be found at the Loader Program Instructions that came out with Protosound 3:
DCS Loader Program Instructions 2.30
This MTH pdf file is "searchable". Search [ chain ] and you can scroll through Instructions to learn about chain files and their use.
See page 8 and 9 of the above Instructions for Chain Files explanation.
Bottom of page 9 - "The first file you see in the list is the .mth file. That's your sound file. The second file you see in the list is another zip file. This is your Code Chain File. You DO NOT need to unzip that file. Simply
extract the sound file (.mth) and the Code Chain File (.zip) to a folder of your choosing as shown
below (it's recommended that you use the My MTH Files folder that is created when you install the
MTH Consumer Loader program):"
The current Loader Program Instructions are V5.0.0 are not "searchable".
http://mthtrains.com/sites/def...0.0_Instructions.pdf
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However I'm so ignorant I immediately got lost in the second paragraph 
. Its just me 
