Just like separate FFB settings are saved per car, separate engine volume settings should be saved per car. In Alpine GT4, the engine sound is too small so I set the engine volume to 100%. But in Formula Pro, the engine is too loud so I should set the engine volume to 20%. It is very disturbing that I should always adjust engine volume when I change to different cars. It would be best if all cars volume get normalized to a certain level, but if it is not possible, at least the engine volume should be saved per car, so that I don't have to adjust it every time I change to a different car.
The normalizing will happen as cars get updated to the new sound system. At some point modding guidelines will also be released so third party content will (slowly) move towards the same standard.
Come to think of it, differect engine volume for each car seems normal. And I think many previous mod cars would remain unchanged. Separate volume saves per car seems an easy solution.
I can foresee a "Speaker DB rating" in the player.json, that scales volumes if your speakers/headphones can reproduce louder sounds, and equalizes the different content if they can't But I think as they update the content, and release modding guidelines, we should at least avoid the huge discrepancy between different content. But that will be an interesting design choice, the mix between different cars with varying real life volume levels.
There should be live adjustment too, key bindings that allow you to turn the volume (overall volume but maybe the engine percentage separately too) up and down. Bizarrely, there are bindings for music volume for the non-existent music player in rFactor.
