Dale G. Kraus

Decoding Sound Decoders

Model railroad sound has come a long, long way. When I was a young boy, I remember “sound” as being the wheezing air whistle of my Lionel set and the thunder of cast wheels on tubular track. I was always a little jealous of my best friend, who had a “Flyer” set that went chuff-chuff down the track, one chuff per wheel revolution. That was pretty much it until the introduction of PFM’s sound system in the mid ’60s and digitally-recorded sound boards in the following decade.

Then came the DCC revolution and the advancement of microprocessers and mini-EEPROMs. Hey! Presto! High quality, realistic sound that will fit into N scale locomotives. Just buy an appropriately sized sound decoder, drop it into your loco, set the address and you’re ready to go!

Well, almost.

Fresh from the package, all decoders, including sound ones, are set to “default” parameters. Some of these must be tweaked to get the most realistic sound performance out of your locomotive. In this article we will deal with diesel loco sound only — steam is a different animal. The CV’s (Configuration Variables) that should be altered to attain really convincing sound are:

  1. CV2 Starting voltage: For convincing sound, set this CV low enough that the loco does not start until the throttle has been advanced a few steps.
  2. CV3 Acceleration: Set to a value around 8-10.  This will allow the loco to increase speed gradually. If the loco still accelerates too fast increase the CV value. These two actions will allow the prime mover sound to “rev up” before the locomotive begins to move.
  3. CV5 Max speed: Most model locos are capable of running way too fast. As a starting point, set this CV to half of the maximum setting. This will slow down the loco and allow the throttle notching effect to perform more realistically
  4. CV6 Mid-range speed: Set to 50% of CV5.
  5. Sound Volume: The CV used for this varies with the decoder manufacturer. See your decoder manual (you did save the manual, right?). Turn this down dramatically. You should not be able to hear the loco a scale mile away! This has three advantages. First, the loud sound, while “Wow, gee whiz!” at first, can quickly become annoying. Second, if you are running more than one loco, the resulting cacophony detracts from the enjoyment of listening to the loco you are running. Third, high sound volume overdrives the small speakers we must use, distorting the resulting sound.

After you have performed the above five tasks, you can go back into the programming mode and tweak other sounds. With many sound decoders you can set the volumes of the bell, whistle, dynamic brakes, etc. See the CV table in you decoder manual. (Which you did not throw out, right?) Doing these five steps will make your loco sound as good as it looks.