Do it the same way with your digital effects. Add the vocals as a side chain input to the compressor on the background track. In Pro Tools they call it a "key input" everyone else seem to call it a side chain.

Or you could set the vocal above the background in the mix and put a limiter on the main bus. Pretty much the same thing when you just have two tracks.

Not all DAWS have Key input Compressors, or side chain compressors. I run Nuendo 3.O and please correct my if I am wrong, but I have not found one yet.

I do have one on my UAD card, but thats a different story...

You could also just automate some fader moves too.

You could probably find a free ducking plugin without too much difficulty. Not ideal, but if you have no other choice...

"free ducking plugin"

http://www.geocities.jp/webmaster_of_sss/vst/index.html#sidechgate

A plee ducking frugin for you.

Codemonkey wrote: "free ducking plugin"

http://www.geocities.jp/webmaster_of_sss/vst/index.html#sidechgate

A plee ducking frugin for you.

Thanks very much for everyone's input and for the link to the plug-in.

I downloaded the plug-in, but has anyone any idea how I use the routing controls? What are they referring to by Channels 1, 2, 3 and 4? Are they tracks? What if my music is already in a single stereo track, how do I route that to Channels 1 and 2?

Any help would be appreciated!

I can't make use of the stereo version of that - I don't have the software.

I have used the mono version however, but I doubt that helps.
Just remember to set your Range control to whatever you want it to duck by, or you'll lose the music altogether.

What software are you using, someone here will likely know if it's possible/how to do it.