Xfce volume buttons (keyboard)

I got these fixes from a couple Internet sources.

Step 1: Make sure you have amixer installed (i.e., from apt-get)

Mute Button

• Applications-->Settings-->Keyboard-->Application Shortcuts (tab)
• If "XF86AudioMute" isn't already mapped, add this command
• amixer -D pulse set Master toggle
• It'll prompt you for the key. Select your mute button

 Volume up / down

• Applications-->Settings-->Keyboard-->Application Shortcuts (tab)
• Map these commands to your volume up and down keys:
• amixer set Master 5%+
• amixer set Master 5%-

That's it!

Tips: you can try these out in the console to see if they work.  Also man amixer is handy.