At Lysk, we process and analyse military voice communications. In other words: we plug radios into computers. Getting the cabling right to run our software is surprisingly hard. And yes, running around in an armoured truck with an oscilloscope is a lot of fun. But what do we even look for when using the oscilloscope? What exactly is carried over a typical audio cable? More importantly: what is 0.7746 Vrms and what do telephone operators have to do with all of this?