A flange is the metal rim or the reel part of a reel to reel tape (also called open reel tape), as opposed to the hub. Years ago when tape machines were used to create delays in audio production a process called flanging was invented. It consisted of recording the same signal on two tapes each playing together and then, using pressure to one of the reel flanges, briefly slowing down one of the machines. The short timing discrepancies that result produce a very pronounced comb filter effect. The effect was often modulated by alternating pressure to each machine’s reels. One machine would slow down relative to the other, and then the second machine would be slowed beyond the first. It was also possible to route some of the signal being played back into the recording circuit to provide regeneration and resonance effects. Later electronic flangers were invented that used a modulated analog or digital delay line, which was mixed back with the dry signal. While much more convenient than the old open reel approach many engineers agree that the electronic units have never sounded as good as the “reel” thing.