Bring all applications to the same level in Windows Volume Mixer
Sometimes the sound level of an application won’t obey the general adjustment or master volume. Whatever you do it keeps playing lower!
To solve this problem, right click on the Volume icon in the system tray and open the Mixer. Then drag the volumes of all your applications to the top (100%).
Now dicreasing the Master Volume will bring also all the other volumes to the same level.
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