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After upgrading from an earlier version of MX where the xfce4-mixer was in service, or for various other reasons, it may be necessary to switch from one to another available mixer. Stock MX Linux provides two mixers, xfce4-mixer and pavucontrol.
The MX mixer control settings can be accessed by right clicking on the volume icon in the system tray/notification area.
This action reveals a dialog where you can change your mixer to use either xfce4-mixer or pavucontrol. To see which one is in service, select preferences from this dialog
Click the Status Icon tab and note the text for the External mixer field is set to pavucontrol.
Close this dialog. Right click on the volume icon again and select Open Mixer
You'll get the pavucontrol version of the mixer.
Close this dialog, right click on the volume icon and select preferences then click the Status Icon tab. When the new dialog appears, change the text for the External mixer field to xfce4-mixer
Close this dialog. Right click on the volume icon again. Select Open Mixer and you'll be presented of the xfce4 version of the mixer