Sounds helps me to flesh out the illusion I seek when playing with my trains. HO scale sound has improved considerably since my first DCC/sound loco, a BLI Hudson in Toronto,Hamilton & Buffalo livery with the QSI decoders of the day (I still have at least six QSI decoders operating, all with the upgraded chip after MTH lost its suit against BLI for patent infringement on PWM and BEMF modulation for low speed control).
Factory default sounds and decoder motion control are awful. No inertia, no momentum, as examples, and the sounds are very close to maximum. This sounds horrible. So, what most of us learn to do, is to mute the Master Volume by around 50-70%, and to alter the motion control CVs so that our engines labour, screech brakes, and slow just like the real items. The sound is vastly improved. For example, I tone down the blow-down and pop-off and injector sounds because they're annoying. In fact, I try to limit myself to any two of my locomotives making sounds at any one time, whether they're idle, one running and the other idle, or both running. I can tolerate that level of sound mix and volume.
You MUST set your Master Volume CV to a middle setting, and adjust others as you need to. This is because sound does not scale on our model layouts any more than smoke or water do. There's no point in having two factory-default sound decoders barking out chuffs from two locomotives that are at opposite ends of a layout that is meant to represent several miles of separation. It's different in the yard, but out on the mains, you should have low volume in the normal operating sounds of any kind of locomotive, diesel or not. You can adjust bells up and down, horns and whistles up and down, but keeping the chuffs and chugs down will really help with attending to, and enjoying, the actions and sounds of the locomotive you are actively working with.