Well how fast are your producing it? Is it analog or digital? What is the interval of music / voice that is required? Are you normalizing it? Or are there variations in magnitude as well as frequency? Once you have these params then you should be able to create a closed form method and figure it out with statistics. (Now actually finding all those things out is probably difficult, what kind of random generator are you talking about? If it literally spits out a random wave for each tiny time interval then you could be there a while, if your adding random frequencies then it could be technically done very soon for certain definitions of music)