From the late 60s onwards, effects (we'll use the shortened form 'FX' from hereon) gradually gained popularity with guitarists. FX units came in many shapes and sizes in the 70s, but by the 80s, two formats had come to dominate - the compact FX pedal, and the 19" rack unit.
Compact pedals offer easy and relatively cheap access to a huge variety of effects, from various types of distortion and overdrive, to chorus, delay, phasing, reverb and pitch shifting amongst others. Compact pedals have simple and obvious advantages - trying new sounds is easy, and pedal setups can be infinitely customised. Three pedals can be connected in six ways, four pedals in twenty-four ways... the possibilities soon become practically endless.
Large pedal setups have obvious disadvantages however. Long chains can introduce more noise than some players find acceptable, and batteries have to be changed frequently, or if power supplies are used, cabling can become complex. FX pedal voltage has recently become almost completely standardised at 9V DC, but in the early days, an FX pedalboard might have required many different power supplies. Like Christmas tree lights, such long chains can fail completely if just one part fails. All else being equal, one would not choose to place a complex array of audio equipment on the floor and subject it to the ravages of dust, dirt and spilt beer!
The rock 'dinosaurs' of the 70s, looking to replicate sounds from expensively produced albums on stage, began to take studio equipment on the road. Studio FX units in this era did one job each, were generally expensive, and required constant maintenance - particularly so in the case of 'trademark' devices such as Leslie speakers and tape delay machines. Chaining them together in such a way that the guitarist could access combinations of sounds quickly was a complex task. While Pink Floyd or Genesis could afford technicians to take care of all this, the average working band could not!
By the mid 80s, studio FX processor design had widely adopted the standard 19" rack design, and solid-state electronics had achieved a high standard of sound quality and reliability. Processors could be permanently connected and transported in a portable rack. While many such units can be operated via footswitch, a full rack could involve a tangle of separate footswitch cables, drastically reducing the practical elegance of such a solution.
A 'multi-FX' processor does exactly what it says on the tin - provide several effects simultaneously. Multi-FX units come in various formats - we'll take a look at the most common over the next few pages.