Audiophiles should be familiar with the concept of measuring THD (total harmonic distortion) in audio gear by playing a tone and watching for similar activated tones called "harmonics" rise up on the spectrum analyzer. But what happens when we use two or more tones? Beyond the associated THD products, we also will see artifacts created by the two interacting, and usually these are happening down in the bass region. In this episode, engineer Darren Myers breaks down IMD and explains how it works, and why it happens more in amplifiers than any other device.