The answer you're looking for is the
"Move Transition" plug-in, made by Exeldro.
I've written a tutorial here, but I've also
made a guide on YouTube as well.
This guide does NOT involve paid software, a GoXLR, Elgato Stream Deck, or any expensive hardware. In fact, my video briefly goes over how to use virtually any controller you can plug into your computer in order to perform tasks like this (and then some!).
The Move Transition plug-in is a filter, or rather 2 filters, and the one you need to use is the "Move Value" filter (the other filter is named "Audio Move").
Like I mentioned before, Move Transition does WAAAYYYY way way way way more than what I'm describing in this comment, which anyone reading can explore for themselves elsewhere. But at any rate, here are the steps to control audio sliders in OBS with hotkeys AS WELL AS hardware:
- Add the filter and name it something like "Volume Slider UP"
- Change the 'Move Value Type' to "Add"
- Change 'Setting - Setting' to "Source Volume"
- Change value to 0.80% (just as a baseline, you can adjust this as desired)
- Change 'Custom Duration' to as low as it will go
- Change 'Easing' to "No Easing"
- Check Off 'Filter only enabled when moving'
- Change 'Next Move On' to "Hotkey"
- Turn on the eyeball icon for the filter
- Duplicate this filter and rename it for volume down
- Insert a hyphen before the 'Setting - Value' number to make it negative
- Turn on eyeball icon to enable filter and close the dialog
- Go into OBS Settings then Hotkeys and locate your audio source and its filters
- Choose the hotkeys you want from this list:
--- 1. Ctrl + (/) (NUMPAD)
2. Ctrl + (*) (NUMPAD)
3. Ctrl + (.) (NUMPAD)
4. Ctrl + Alt + 1 (NUMPAD)
5. Ctrl + Alt + 2 (NUMPAD)
6. Ctrl + Alt + 3 (NUMPAD)
7. Ctrl + Alt + 4 (NUMPAD)
8. Ctrl + Alt + 5 (NUMPAD)
9. Ctrl + Alt + 6 (NUMPAD)
10. Ctrl + Alt + 7 (NUMPAD)
11. Ctrl + Alt + 8 (NUMPAD)
12. Ctrl + Alt + 9 (NUMPAD)
13. Ctrl + Alt + 0 (NUMPAD)
14. Ctrl + Alt + (/) (NUMPAD)
15. Ctrl + Alt + (*) (NUMPAD)
16. Ctrl + Alt + (-) (NUMPAD)
17. Ctrl + Alt + (+) (NUMPAD)
18. Ctrl + Shift + (/) (NUMPAD)
19. Ctrl + Shift + (*) (NUMPAD)
20. Ctrl + Shift + (-) (NUMPAD)
21. Ctrl + Shift + (+) (NUMPAD)
22. Ctrl + Alt + Shift + (/) (NUMPAD)
23. Ctrl + Alt + Shift + (*) (NUMPAD)
24. Ctrl + Alt + Shift + (-) (NUMPAD)
25. Ctrl + Alt + Shift + (+) (NUMPAD)
26. Ctrl + F2
27. Ctrl + F8
28. Alt + F2
29. Alt + F3
30. Alt + F5
31. Alt + F6
32. Alt + F7
33. Alt + F8
34-42. Ctrl + Alt + Shift: ( [ ) ( ] ) ( \ ) ( ; ) ( ' ) ( , ) ( . ) ( / ) --- KEYBOARD, NOT NUMPAD
43-51. Ctrl + Shift: ( [ ) ( ] ) ( \ ) ( ; ) ( ' ) ( , ) ( . ) ( / ) --- KEYBOARD, NOT NUMPAD
52-60. Ctrl + Alt: ( [ ) ( ] ) ( \ ) ( ; ) ( ' ) ( , ) ( . ) ( / ) --- KEYBOARD, NOT NUMPAD
Any questions, again I encourage you to watch my video. Otherwise feel free to ask!