As a musician I often need to learn new songs, and it can be difficult to hear individual instruments in recordings I want to study. I have often wished for an easy way to eliminate or reduce the vocals and isolate the instruments. Various hardware and software solutions exist but they tend to be expensive or inconvenient. I wanted a cheap method that I could use anywhere, on any device with a 1/8" stereo headphone jack. Then, one night, I was fiddling with a pair of headphones with a defective plug. When moved a certain way, it gave exactly the vocals-canceling effect I had been looking for!