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#10 describes how to use Apple Script “set volume output volume” in Automator Quick Actions (services) that can be triggered by F11/F12. The example uses 5 as increment, but it can be 1, 2, 3 … depending on how much you wish to turn up/down the volume. In this way, F11 can be used as Option + Shift + Volume Down and F12 as Option + Shift + Volume Up.