I switched to a new laptop, and noticed that the volume down key stopped working. I had rsynced all the files in my home dir to the new laptop, and it turns out one of these needs a tiny change.
In the i3 window manager, this setting:
pactl set-sink-volume 0 -- -5%
no longer worked. But this:
pactl set-sink-volume 0 -5%
does. The difference is two dashes.
Earlier, I detailed how to get the multimedia keys working on a Thinkpad 400s, when using the i3 window manager. For the Thinkpad Carbon X1 (1st Generation) I simply removed the two dashes.
# audio soft keys bindsym XF86AudioRaiseVolume exec --no-startup-id pactl set-sink-volume 0 +5% bindsym XF86AudioLowerVolume exec --no-startup-id pactl set-sink-volume 0 -5% bindsym XF86AudioMute exec --no-startup-id pactl set-sink-mute 0 toggle bindsym XF86AudioMicMute exec --no-startup-id pactl set-source-mute 1 toggle