Watch the Diminished Fifth online guitar lesson by Kai Eckhardt from Atomic Bass: Reactive Intervals
The diminished fifth is also referred to as the augmented fourth, a b5 (flat five), a #4 (sharp four) or the tri-tone. It is called that because it is made up of three whole tones. Listen to how Jimi Hendrix kicks off "Purple Haze" for a prime example. In the Middle Ages and the Renaissance it was called the Devil's interval because of its dissonant sound. In jazz, however, it shows up as a stabilizing force, giving a dominant seven chord its stability. (Between the 3rd and the b7, two of the most characterizing intervals defining the bluesy sound of that chord). Heavy metal is also fond of this interval as you can imagine and at the end of the day you define it for yourself. But before you can do that, you've got to start shedding it! It starts with a monster slide up a b5 and then continues on its diabolic mission (just kidding, it's just a sound y'all). We shall choose three tonal centers: G, Bb and Db.