If I use my headphone (EarPods), and have just normal music volume, and use some app such as Pokémon Go and have the sound effect on, then the sound effect will blow my ear drum off. (say, when the Appraisal texts are showing one by one, or after the items are dispensed from the Pokéstop).
I remember in the old days, on iOS, we can adjust the Music volume to be louder, and then the master volume to be lower. So in this case, the game's sound effect will go down together with the master volume.
I understand some people may suggest, it is up to the app's developer. But what if some users do want that sound effect to be louder? Or, if each app is to implement its own volume adjustment, then shouldn't the Music app have it too? I think one good way that it works is that each sound channel can be adjusted, just like on a Mac or PC, when you can adjust the master volume to be lower, and then adjust the music volume to be higher, so that now all the other sound channels (games, apps) will be secondary, because it went down together with the master volume. Can this be done on the iPhone (which if not mistaken, could be done in the old days)?