[Openal] Get current volume for a source

[The Big Uno]

Hello all,

I am trying to implement a VU Meter style widget by pulling the 
currently playing volume of a given source.  Note that this is not the 
gain of the source; I want the number to be either the raw value of the 
sound frame at the time I call the function, or the raw value * current 
gain set for the source.  Does anyone have an idea on what function I 
could call for this?

I would like to get this value for just a certain source, not the entire 
OpenAL environment.  The VU meters I am making are going to be on a 
per-channel level, with each source logically mapped to a certain 
channel.  Think of the giant mixing boards with a VU meter for each 
input source for an idea of what I am trying to do here.

(On a side note, I am actually using JOAL - Java wrappers for the OpenAL 
functions - which I believe is currently using the OpenAL 1.0 
specification.  The JOAL methods map quite closely to the underlying 
OpenAL API, which is why I am asking here and not on the JOAL forums.  
If you can get me the OpenAL function, that would be good enough for me.)

Thank you!