While at the Liverpool exhibition, I was talking to Ian Phemister about an ESU ROD sound file that he had purchased. While I have not heard the ROD sound file, Ian explained that you could 'drive' the locos sound using throttle speed step inputs.
While most ESU users are aware, when you drive the loco, you set a speed setting and the locomotive sets off. In most cases when the locomotive is accelerated quickly, depending on how the sound file is set up, the locomotive will usually start to chuff louder, simulating a hard working engine. Once the difference in requested speed and actual locomotive speed closes, the locomotive automatically transitions into a quieter chuff sound. When I say 'in most cases' I mean that not all ESU sound projects are the same in how they behave. There are many steam projects available on their website and many have slightly different drive architecture.
A few blog posts back I came up with a method to push the drive sounds into the acceleration sound (hard working chuff) area using a function button. This does work well and allows the locomotive to move at a constant speed working hard (does not automatically revert to quite chuff sounds). While this option is good, some people do not have spare function buttons available to use as a drive sound modifier.
While I have not heard Ian's ROD file, I decided to have a play around with my C38 sound file. I have modified the drive sound transition settings to allow the locomotive to remain playing the acceleration sound files, even when the speed requested equals actual locomotive speed. The acceleration threshold has also been lowered to make it more responsive into the acceleration area. This could probably be relaxed just a little so the locomotive can be more easily crept up to speed quietly, perhaps in the case of a light engine movement or a descending start. More refining required.
Once the locomotive has reached the user's desired speed they can leave it there and let the loco work hard or they can pull the throttle back one speed step and relax the chuff sound into a quieter beat. Once quietly chuffing along, if wanted the throttle can be moved back one more speed step and the locomotive will coast along with no chuff sound, simulating a shut off regulator setting.
While this method works well, one negative is that you need to reduce the speed of the locomotive one speed step to affect the sound change. While it is not to big a change in speed you can still detect the slowing chuff rate.
Moving ahead with this, I would like to have this option selectable. With the press of a button you could select between the two drive modes. I know this would also use a function button but this could be moved to a less used number.
I have made a short video of the C38 running. Would like some feedback on this, especially from those that have used the ROD file.