Quick way to mute sound

Hi,

I have my iMac hooked up to an external audio interface via Firewire. Most of the time while I'm working, I listen to an internet radio station, which I have open in a separate browser window hidden behind the main browser window. If I need to quickly mute the sound – for instance, when I get a phone call – this is not always easy: I have to switch to the browser, then switch to the relevant browser window, then click on the "stop" or "mute" buttons on the internet radio player. I used to use a third party radio player app (Snowtape) with a customisable keyboard shortcut to mute and unmute the sound, but I had to stop using it; for some reason, it would no longer play nice with my favourite radio station once I upgraded to Lion.

So, my question: is there any way of setting up a system-wide keyboard shortcut that will toggle sound on and off?

Thanks,

Rob