What you're looking for is called a gate or expander. I'm sure there'll be something in the /Examples folder, but the process is really quite simple; you need to avg~ the incoming signal then use that to open a gate~. You set a threshold at which you want the gate~ to open so that the signal is let through only when the average signal level is above the threshold, i.e. during the loud bits. Look at >=~ for setting the threshold and opening/closing your gate~ and maybe trapezoid~ or line~ to prevent clicks when your gate is opened/closed. I could post an example, but it will be much more instructive/fun for you to build it yourself ;-) Cheers Roger

I started making a noise gate for you, went something like this:

that's just one way of doin it. And I too encourage you to try making one yrself first, it's a fun exercise :) I think you might also be able to do noise gating with omx.comp~ but I can't figure out how. And surely there are other examples of gating on the forums. Definitely don't "turn audio on and off". When it's off, none of the MSP objects (anything with a ~ at the end) will function :P