Can't open pavucontrol in xfce - sound not configured
 

I am trying to open pavucontrol in debian with the xfce desktop.
The error message is:

I am having trouble getting sound and configuring the settings.
There is no sound setting in the Settings Manager of xfce.
Also, every time I change alsamixer to my hdmi sound card it keeps going back to the default analog sound card when I exit the program.

How can I access the system settings on the desktop or do I need to change a file setting from the terminal?

My radeon sound card has given me problems with my previous debian install. From this, I've learned some changes I need to make which rectify the problem.
I've done the following:

Ensure etc/apt/sources.list includes 'contrib' and 'non-free'
Install relevant firmware:
Ensure /etc/default/grub has 'radeon.audio=1' added:
When I open alsamixer from the terminal it defaults to the analog sound card which isn't being used. I need to set the sound card to the radeon hdmi one but don't know how.
There is no sound icon on this xfce DE under system settings!

If the card you want is listed as 1 and the analogue as 0, try creating a file $HOME/.asoundrc to contain
defaults.pcm.card 1
defaults.pcm.device 0
defaults.ctl.card 1
Then you need to log out and in again. No guarantees, though: Debian sound is a black art. I remember one case where the numbering of the devices could change from boot to boot!

My previous install on a different partition where the sound is working doesn't have a .asoundrc file.
I have come across some solutions referring to the .asoundrc file. However, since the first install doesn't even have the file, I'm wondering if the answer is somewhere else.

One thing I haven't done is change the system settings for sound on the desktop. But for some reason there is no icon for it on this xfce desktop!
I'm thinking that there must be a problem if the xfce desktop doesn't even have a system setting for sound...

Well, I've got pavucontrol working!

I tried opening pavucontrol from the terminal, and nothing happened.
So I tried installing it again. It installed correctly without saying that the program was already installed.

So the error message for the program must have been due to a broken install.
I can now open the program via desktop and terminal.
Still got no sound though.

I don't think any distro creates that file by default. It's something you make yourself if you need it in very hands-on distros like Debian, Arch, or Slackware.

The command
aplay -l
should list your devices and confirm which is numbered 0 and which is 1. If the sound card isn't listed, try
cat /proc/asound/modules
to see if the kernel module for it is loaded. If it isn't, then you need to install that from Debian and reboot.

The hdmi card is listed under 'aplay-l':
The problem I'm having is being able to change system settings to default to the hdmi sound card.
But now I'm beginning to wonder if the .asoundrc file will do this anyway.
I'll give it a try.