At work I use a combination of Mac OS X (Tiger) and a Windows XP laptop (mainly for developing web applications running in a Linux environment — go figure). I currently use Synergy to share the keyboard and mouse on my Mac with my XP machine. This really is an awesome program. It can be a pain to setup on non-windows machines, but it’s well worth the time and effort. I plug my headphones into my PC for mail and instant message notifications and to listen to music. My problem arises when I’m doing something on my Mac and I come across something that I want to listen to. I could blast it over the built in speakers, but I’d prefer to not have other office inhabitants loathing me.

I finally took the time to get a 1/8″ male to male stereo cable to connect the two audio systems together. At first I connected the headphone out of the Mac to my line in of my laptop. This worked fine, but the SNR on the laptop of the line in port wasn’t all that great. I wasn’t about to pollute my ears with the subtle sounds of a hissing cat. I decided to reverse the process: the output of the laptop goes to the line in of the Mac. Perfect — I play the sound on my PC, and I see the meter pumping in the sound settings. But I can’t hear a darn thing! Apparently, an out of the box Mac cannot route the line in port to the ouput.

After a few minutes of “Googling”, I found LineIn. This allows you to take any input and assign it to any output. Go figure. At least it’s freeware.