What Is Intermodulation Distortion?

from The Hifi Podcast with Darren and Duncan · host Duncan Taylor, Darren Myers

"Not all distortion is horrible" is a notion many come to observe at some point along the audiophile journey. Maybe that's not the best way to put it. How about, "some distortions are less horrible than others".In past episodes of The Hifi Podcast, Darren and Duncan have talked about complex versus simple distortions, and the fact that simple circuits and simple devices distort simply. And simple distortion is much, much more tolerable to our ears.Intermodulation distortion (IMD) is a complex beast of a distortion, creating byproducts of the difference between competing frequencies. A shimmering cymbal hit with fundamentals of 9KHz and 9.1KHz for example will produce an IMD product of 100Hz. Yes, that's right - artificial bass noise created from within the amplifier, for just these two tones. Imagine what happens with real music playing!This week's episode focuses on IMD and explains why amps are the biggest culprits of this sonic bugaboo.Also in this episode, the guys answer a couple questions about system battery power and round listening rooms. The album of the week is a killer sounding new joint from perhaps the biggest name in bluegrass right now.  This podcast is powered by CommonGround Cables Whisper power cable. Read customer reviews and order your own at www.commongroundcables.com.Find all of our album recommendations in one place, at www.thehifipodcast.net.

What this episode covers

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.