Possibly the greatest invention in the history of audio
Possibly the greatest invention in the history of audio is the rotary controller, otherwise known as the knob!
Just because something is commonplace doesn't mean it isn't a great invention. Everyone has a telephone for instance, and our lives would be massively different without that.
The rotary controller or knob has two applications - it can be used as a continuous controller, as in the majority of EQ controls, or it can be used to control a switch. Rotary switches have gone out of fashion somewhat as they are much more expensive than potentiometers. However they are still appreciated in applications such as theater, where repeatability is important, and mastering, where the precision of a switched setting is appreciated.
In both of these applications, the knob performs two functions simultaneously - it controls the position of the potentiometer's wiper, or the setting of the switch. In the process of doing that, the knob's pointer also provides an indication of the potentiometer's or switch's setting.
Having the ability to control a parameter and display its value simultaneously is a great virtue. To do the same on a digital console requires a special controller that incorporates a ring of LEDs around it to indicate the parameter value. Otherwise, the physical position of the digital control does not necessarily bear any relation to the parameter it controls.
In the early days of digital synthesizers and effects units, back in the 1980s, it was thought that the knob was a relic of a bygone age. Such equipment was provided with a pair of up/down buttons, and a display to indicate parameter values numerically.
People who said they preferred knobs were regarded as audio dinosaurs for their unwillingness to leap into the abyss of new-fangled technology.
However, time has proven that the knob is a simple and intuitive interface, hence its graphic inclusion in high-end audio plug-ins.
Something tells me that the knob, or at least a graphical representation of the knob, still has a great future ahead of it.
Has anything else in audio lasted as long?