[sdiy] line levels

[trip at blackstar.myip.org]

could someone provide a definition of 'line level' in terms
of voltage range, impedance, and such? ive decided to build
a mixer first before i start a full synth. i'm planning on
using something like an lm1036 to control each channel,
but i'm not too sure about how to handle the input and output 
stages. i'd like something simple, but i also wouldn't mind
some extra complexity for better quality. any thoughts on
how to build these sections?