- There is a master sound volume. Only root can change this.
- There is a per-user sound volume. A user can only change her/his own.
- There is a per-application sound volume. This is what applications change with their sound control. Applications do not change the per-user volume unless they are specifically for that purpose, like
alsamixer. A dedicated volume control program can control application volumes, in case the application doesn’t have a control. - If an application wants to provide more detailed control over its sound (e.g. a music track and a sfx track) it ??. Mixes them itself, and only sends one track to the OS? Sends both, but after changing their volume, and with the same application name so the per-application control affects both? Exposes both to the OS entirely, and requests separate volume controls for them (which it then affects using its own in-app controls)?
All values are, of course, multiplied before affecting the sound. Values greater than 100% are allowed.
This does not specify how it interacts with the actual speakers (perhaps volume control on the speakers changes the master volume?).