Flange was created by accident in a studio. It was found that if you played back a reel-to-reel tape of the guitar track and held up the reel with your hand and let it go it would catch up with the other tracks causing what would become known as flanging. The best way I can describe this effect is like riding a roller coaster. You go up the hill slowly (The engineer holds the reel back with his hand) and when you hit the top you pause for a millisecond and then you rush to the bottom very quickly (The engineer lets go of the reel to let it catch up with where it
should be) and then you start up the hill again slowly (The engineer holds it with his hand again) to do it all over again. The other instrument tracks would be played normally and
the guitar track would be held up and let go to catch up at regular interverals throughout the track. This created a “whooshing sound” on the guitar track. Kind of like a jet engine.
Thanks to electronic and digital technology we can reproduce this effect with stomp boxes and multi effects called flangers. Flange moves in and out a constant and steady predetermined speed that you set.