Cf le readme du code source de mumble :
Mumble is a voicechat program for gamers written on top of Qt and Speex.
Code:
           M U M B L E

 A voicechat utility for gamers

  http://mumble.sourcforge.net/

      #mumble on freenode

Mumble is a voicechat program for gamers written on top of Qt and Speex.

There are two modules in Mumble; the client (mumble) and the server
(murmur). The client works on Win32/64, Linux and Mac OS X, while the
server should work on anything Qt can be installed on.

Note that when we say Win32, we mean Windows XP or newer.

Running Mumble
==============

On Windows, after installation, you should have a new Mumble folder in your
Start Menu, from which you can start Mumble.

On Mac OS X, after installation, you can launch Mumble from your Applications
folder.

Once Mumble is launched, you need a server to connect to. Either create your
own or join a friend's.

Running Murmur on Unix-like systems
===================================

Murmur should be run from the command line, so start a shell (command prompt)
and go to wherever you installed Mumble. Run murmur as

murmurd [-supw <password>] [-ini <inifile>] [-fg] [v]

-supw   Set new password for the user SuperUser, which is hardcoded to
        bypass ACLs. Keep this password safe. Until you set a password,
        the SuperUser is disabled. If you use this option, murmur will
        set the password in the database and then exit.

-ini    Use a inifile other than murmur.ini, use this to run several isntances
        of murmur from the same directory. Make sure each instance is using
        a separate database.

-fg     Run in the foreground, logging to standard output.

-v      More verbose logging.

Running Murmur on Mac OS X
==========================

On Mac OS X, Murmur is available inside your Mumble application bundle. If you
copied the Mumble program into your Applications directory, you should be able
to run it by executing:

 /Applications/Mumble.app/Contents/MacOS/murmurd -v -fg

in a Terminal. For more information, please see the 'Running Murmur on Unix-
like sytems' above.

To easily override the default Murmur configuration, a murmur.ini file can be placed in
your user's 'Library/Preferences/Mumble/' directory.

Example configuration files and other scripts can be found inside the Murmur
directory of the Mumble installation disk image.

Running Murmur on Win32
=======================

Doubleclick the Murmur icon to start murmur. There will be a small icon on your
taskbar from which you can view the log.

To set the superuser password, run murmur with the parameters '-supw <password>'.

Bandwidth usage
===============

Mumble will use 10-40 kbit/s outgoing, and the same incoming for each user.
So if there are 10 other users on the server with you, your incoming
bandwidth requirement will be 100-400 kbit/s if they all talk at the same time.