1. Go to System Settings → Keyboard → Shortcuts → Application Shortcuts.
2. Click + to add a new keyboard shortcut.
3. amixer -D pulse sset Master 5%+ and click Apply.
4. Press combination you want to use. I used super and =
5. Click + to add a new keyboard shortcut.
6. amixer -D pulse sset Master 5%- and click Apply.
7. Press combination you want to use. I used super and –
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