Expression-pedals, Midi, CV and Apps
The first pedal that could be controlled with an expression-pedal in real time was the Uni-Vibe. The advantage was that you could adjust the swiftness without taking the hands off the strings. Later this function could also be found in Auto-Wahs. In this way the pedal could be controlled just like a real Wah.
Likewise, the tempo of certain delays without tap tempo can be set with an expression-pedal.
Only for a short time there was the T.I.P. third hand pedal. The connector of this pedal could have been screwed right on the pot of any pedal. Thereby any parameter of a pedal could have been controlled mechanically with a pedal.
What seems to be omnipresent in the world of synthesizers, (still) appears pretty unusual to guitarists: the control with CV (Control Voltage). The level of Control Voltage goes from 0V up to 5V.
According to the increase of the voltage the parameter of a pedal can be controlled as with an expression-pedal.
Electro Harmonix makes it possible to control many of their pedals with an expression-pedal as well as with CV. And also the pedals of Chase Bliss and, of course, the Moggerfogger by Moog (which originally come from a synthesizer) enable you to do so.
Even if many guitarists refuse to integrate midi into their setup, it also can be suitable. Especially since Eventide put the H9 on the market, which has got a midi clock. By that the H9 can be synchronized with the song. Or you can load the presets automatically. If you connect more than one midi-compatible pedal or for example the Line6 M5 with the Eventide H9, you are able to synchronize delays and tremolos.
Midi controller like the Moog MP-201 form a complete control center. They are able to control the presets of various pedals or the function of an expression-pedal for analog pedals with an expression-pedal-jack as well as digital pedals with midi.
At least since TC Electronic launched the Toneprint Editor for their pedals, these can also be controlled by app. The same applies to the pedals of Source Audio. Next to the parameters which can be adjusted by the knobs, several other parameters can be controlled in this way.