Ring modulator as band pass filter

Here's a trick I stumbled across-- if you send the same source into the two halves of a ring modulator (in this case, a Frostwave Blue Ringer), it acts like a band pass filter.

I apologize for the horror movie lighting-- we had a green light bulb left over from Halloween and I couldn't resist. I think it looks like a "Suspiria" blooper, somehow. Enjoy!